Cold idle / thermowax help
11-10-16, 01:20 PM
#1
Cold idle / thermowax help
In July I installed a new engine into my 87.5 gxl. The engine is an s4 turbo, mildly ported, utilizing na rotors. It's run currently on the stock N333 ecu and stock injectors and supplied with fuel via an fd fuel pump. The aws is disconnected.
I've been having a few strange drivability problems that I'd like a little help sorting out.
First off, the cold idle is ridiculous. 2,500 to 3,000 revs until it warms up and the thermowax comes off. In doing some research, I found that I might be able to correct this by fiddling with the 'cam adjusting screw'. This did very, very little for the cold idle speed, but it did speed up the time it took for the thermowax to come off and for the warm idle to happen. However, a side effect was that once warmed up the car would no longer idle. I decided to set it back where it was. I've assumed I was making the wrong sort of adjustment, so a little clarity is desired.
Second, mostly when the engine temperature is cold, it holds onto revs between gear changes / slightly revs up between gear changes. This is not only annoying, but embarrassing.
Timing should be good, I've carefully adjusted the throttle position sensor and the idle mixture.
It may be worth mentioning that I've got no bac valve. I physically have one, but it's reused from my last NA engine with the tube rotated so that it works on the turbo engine. It is not plugged in. This does not appear to have any negative side effects, even with the power steering... It does however mean that I've got one less idle adjustment, and that's annoying. With the bac valve plugged in, cold idle is over 3,000 revs and I simply am not interested in listening to that kind of racket early in the morning ;-)
Any help would be appreciated. I'm not a huge moron, but I'm starting to feel like one. In my opinion this is a matter of getting the thermowax adjusted properly.. I've never had one that needed adjustment, so this is new to me.
I've been having a few strange drivability problems that I'd like a little help sorting out.
First off, the cold idle is ridiculous. 2,500 to 3,000 revs until it warms up and the thermowax comes off. In doing some research, I found that I might be able to correct this by fiddling with the 'cam adjusting screw'. This did very, very little for the cold idle speed, but it did speed up the time it took for the thermowax to come off and for the warm idle to happen. However, a side effect was that once warmed up the car would no longer idle. I decided to set it back where it was. I've assumed I was making the wrong sort of adjustment, so a little clarity is desired.
Second, mostly when the engine temperature is cold, it holds onto revs between gear changes / slightly revs up between gear changes. This is not only annoying, but embarrassing.
Timing should be good, I've carefully adjusted the throttle position sensor and the idle mixture.
It may be worth mentioning that I've got no bac valve. I physically have one, but it's reused from my last NA engine with the tube rotated so that it works on the turbo engine. It is not plugged in. This does not appear to have any negative side effects, even with the power steering... It does however mean that I've got one less idle adjustment, and that's annoying. With the bac valve plugged in, cold idle is over 3,000 revs and I simply am not interested in listening to that kind of racket early in the morning ;-)
Any help would be appreciated. I'm not a huge moron, but I'm starting to feel like one. In my opinion this is a matter of getting the thermowax adjusted properly.. I've never had one that needed adjustment, so this is new to me.
11-10-16, 02:02 PM
#2
The high cold idle of close to 3k is normal for about 17 seconds if the temp of the coolant is above 62 degrees or so. I would suspect your living in Vermont at this point in the year that your coolant temp in the morning is below the threshold thus you should not be incurring the 3k cold start rev. You need to make sure pin 1H of ECU has the proper voltage reading as it should read below 1.5 volts w/key to on if the coolant temp is above 62 otherwise it should be higher than 1.5 volts by a fair amount.
Now if the coolant temp was above 62 degrees and the cold idle starts for just 17 seconds that is one thing but if it lasts longer than that you then need to look at a few things. The FSM shows the correct setting for the cam on the thermovalve thus you need to set it to that and not otherwise. Secondly, the air bypass valve and BAC work in concert w/each other.
If you had a large vacuum cap you could place it on the screw of the thermovalve which rests against the metal rod which protrudes from the thermovalve. In doing so it will eliminate the cold start rev.
And you have not described what the car eventually idles at or how it does not idle for that is a vague description to say the least.
Now if the coolant temp was above 62 degrees and the cold idle starts for just 17 seconds that is one thing but if it lasts longer than that you then need to look at a few things. The FSM shows the correct setting for the cam on the thermovalve thus you need to set it to that and not otherwise. Secondly, the air bypass valve and BAC work in concert w/each other.
If you had a large vacuum cap you could place it on the screw of the thermovalve which rests against the metal rod which protrudes from the thermovalve. In doing so it will eliminate the cold start rev.
And you have not described what the car eventually idles at or how it does not idle for that is a vague description to say the least.
11-10-16, 05:11 PM
#3
The high cold idle of close to 3k is normal for about 17 seconds if the temp of the coolant is above 62 degrees or so. I would suspect your living in Vermont at this point in the year that your coolant temp in the morning is below the threshold thus you should not be incurring the 3k cold start rev. You need to make sure pin 1H of ECU has the proper voltage reading as it should read below 1.5 volts w/key to on if the coolant temp is above 62 otherwise it should be higher than 1.5 volts by a fair amount.
Now if the coolant temp was above 62 degrees and the cold idle starts for just 17 seconds that is one thing but if it lasts longer than that you then need to look at a few things. The FSM shows the correct setting for the cam on the thermovalve thus you need to set it to that and not otherwise. Secondly, the air bypass valve and BAC work in concert w/each other.
If you had a large vacuum cap you could place it on the screw of the thermovalve which rests against the metal rod which protrudes from the thermovalve. In doing so it will eliminate the cold start rev.
And you have not described what the car eventually idles at or how it does not idle for that is a vague description to say the least.
Now if the coolant temp was above 62 degrees and the cold idle starts for just 17 seconds that is one thing but if it lasts longer than that you then need to look at a few things. The FSM shows the correct setting for the cam on the thermovalve thus you need to set it to that and not otherwise. Secondly, the air bypass valve and BAC work in concert w/each other.
If you had a large vacuum cap you could place it on the screw of the thermovalve which rests against the metal rod which protrudes from the thermovalve. In doing so it will eliminate the cold start rev.
And you have not described what the car eventually idles at or how it does not idle for that is a vague description to say the least.
The accelerated warmup has always been disconnected, it's one of the first things I've done with each of these that I've owned. I mentioned that in my original post. I achieve this by simply disconnecting the sensor on the lower left hand corner of the radiator, which I believe to be common practice for those who don't want to deal with the aws or always starting the car in gear.
I had already back probed the 'thermosensor' at the ecu, and it's kosher.
I can pull the throttle body again, but the last time I had it out, I checked the cam markings on the thermowax setup against what I've found on the forum through searching, and it checked out. This is the main reason I've been scratching my head about adjusting the thermowax. It should be fine in theory, but in action it does not seem to behave as I would expect.
As for the vague description of the idle......
...when I said that after adjusting the cam screw resulted in no idle when it was at NOT, I literally (and obviously) meant that it won't idle. It drops low enough that it simply stalls out, so I'm not sure how I can better describe that for you.
Under normal circumstances, setting the screw back to where it was before, it'll idle at a solid 1,000 once it's reached NOT. This is how it has behaved since this engine went in. No vagueness here, I sincerely hope.
This weekend I'll likely pull the throttle body and ensure the markings have ended up back where they need to be. I'll probably try and clean the Coolant passages out a little better than I did when I installed the engine (all I used was some compressed air), and I may remove the thermowax itself to check it for functionality with hot water.
I read here on the forum that the thermowax setup can be adjusted as to dictate the cold idle speed, but there's no mention of what needs to be adjusted to make that happen, and I'm not a fan of blindly turning set screws. Thoughts?
Additionally, could the lack of a turbo bac with no bypass screw be partially to blame for this? I can't imagine, as I've always been under the impression that you cannot adjust and set your idle until it's fully warm, with the initial set coupler jumped, and also adjusting the tps, idle mixture, and the bypass screw essentially in unison to achieve the correct balance.
11-10-16, 05:48 PM
#4
The static setting of the primary throttle plate is the baseline for idle- this is the amount the throttle is cracked open when the thermowax is fully warm and (theoretically) completely out of the way.
If you pull the throttle body again you might check that after you get all the cams/linkage arranged to spec.
If you pull the throttle body again you might check that after you get all the cams/linkage arranged to spec.
11-24-16, 08:05 PM
#5
Last Sunday I pulled the throttle body and took a second look at the thermowax setup. At 77ish degrees, the center of the roller was lined up with the wrong mark. I must have been looking at it upside down or something when I checked it last. So, I began turning the cam adjust screw to bring the roller in line with the right mark. In doing so, the screw gets 'maxed out' to the point where it begins to fully compress the little spring and then some. That to me does not seem normal. But, whatever, to be thorough I set it where the FSM says it needs to be and gave it a shot.
Putting the throttle body back on the car and starting the engine dead cold, the idle was pretty much bang on at 1,500rpm, and as the engine began to warm up, it reduced idle speed down towards a thousand. Once it neared normal operating temperature though, the idle started getting too low and the engine began to labor. So naturally, once fully warm, it would not hold an idle at all. You could of course keep it running with the throttle, but it would not idle.
These are the results I got before when I attempted to 'blind adjust' the cam adjusting screw as described in my original post. Also like last time, I ended up removing the intercooler and adjusting the screw counter clockwise bit by bit until I got it to a point where it'd idle with the engine at temperature. Which puts it right at where it was before I started trying to figure this out... Also the same result is the cold idle speed. 2,500-2,700 rpm when cold, 800 - 1000 when hot.
Still at square one, basically. Very frustrating.
Clokker, I guess I'll pull it again this weekend and have a look at that.
Putting the throttle body back on the car and starting the engine dead cold, the idle was pretty much bang on at 1,500rpm, and as the engine began to warm up, it reduced idle speed down towards a thousand. Once it neared normal operating temperature though, the idle started getting too low and the engine began to labor. So naturally, once fully warm, it would not hold an idle at all. You could of course keep it running with the throttle, but it would not idle.
These are the results I got before when I attempted to 'blind adjust' the cam adjusting screw as described in my original post. Also like last time, I ended up removing the intercooler and adjusting the screw counter clockwise bit by bit until I got it to a point where it'd idle with the engine at temperature. Which puts it right at where it was before I started trying to figure this out... Also the same result is the cold idle speed. 2,500-2,700 rpm when cold, 800 - 1000 when hot.
Still at square one, basically. Very frustrating.
Clokker, I guess I'll pull it again this weekend and have a look at that.
11-26-16, 09:39 AM
#6
are you sure you have your AWS and BAC solenoids disconnected for the tests?
the thermowax doesn't generally have control of idle speed to that extent.
also, if your set screw is to the point of mashing the springs and the cam is still on the roller, something is wrong with your throttle body. someone perhaps modified it and didn't reassemble it correctly, or the thermowax is stuck in the out position(i guess it can happen, rarely, but i don't recall if this would be the result but the opposite would likely be true).
the thermowax doesn't generally have control of idle speed to that extent.
also, if your set screw is to the point of mashing the springs and the cam is still on the roller, something is wrong with your throttle body. someone perhaps modified it and didn't reassemble it correctly, or the thermowax is stuck in the out position(i guess it can happen, rarely, but i don't recall if this would be the result but the opposite would likely be true).
Last edited by RotaryEvolution; 11-26-16 at 09:43 AM.
11-26-16, 09:56 AM
#7
I'm positive...those wires havent touched the sensor on the radiator in years.
The bac valve is an N/A unit with the inlet pipe turned to work on a turbo car. Having it connected to the harness does nothing positive, because there's no bypass screw to adjust the idle. The engine is pretty strong, so additional loads like the power steering being used at idle doesn't really affect the engine negatively.
It is only physically there for the Coolant hose routing, and to prevent leaks. I know that this is not ideal, and I have been on the prowl to find a good n332 bac valve. I'm not sure how much adjustment the turbo bac provides for idle speed, but I know that some people choose to remove the bac altogether and still achieve idle, albeit slightly high. I can't see this causing my excessive cold idle speed though. Am I wrong?
The fact that setting the cam roller to the correct matching mark gives me an appropriate cold idle speed makes me think that it should definitely be there.. But the screw being so compressed that it begins squashing the spring just seems wrong, like something else is not adjusted properly that makes that cam adjustment screw not fall within its normal 'range' when you match the mark to the roller. Does that make sense?
This is supposedly an unmolested throttle body and I can't imagine why it would have been adjusted otherwise, but who knows.
I have a feeling that whatever is causing my problem will turn out to be something so stupid that the 'aha!' moment might be bittersweet.
The bac valve is an N/A unit with the inlet pipe turned to work on a turbo car. Having it connected to the harness does nothing positive, because there's no bypass screw to adjust the idle. The engine is pretty strong, so additional loads like the power steering being used at idle doesn't really affect the engine negatively.
It is only physically there for the Coolant hose routing, and to prevent leaks. I know that this is not ideal, and I have been on the prowl to find a good n332 bac valve. I'm not sure how much adjustment the turbo bac provides for idle speed, but I know that some people choose to remove the bac altogether and still achieve idle, albeit slightly high. I can't see this causing my excessive cold idle speed though. Am I wrong?
The fact that setting the cam roller to the correct matching mark gives me an appropriate cold idle speed makes me think that it should definitely be there.. But the screw being so compressed that it begins squashing the spring just seems wrong, like something else is not adjusted properly that makes that cam adjustment screw not fall within its normal 'range' when you match the mark to the roller. Does that make sense?
This is supposedly an unmolested throttle body and I can't imagine why it would have been adjusted otherwise, but who knows.
I have a feeling that whatever is causing my problem will turn out to be something so stupid that the 'aha!' moment might be bittersweet.
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11-26-16, 11:54 AM
#8
Alternatively...
In the name of saving time and hassle, what about swapping my throttle body out for a jdm s5 turbo unit? I haven't dug it out of my parts stores yet, but I *think* the only difference is the twin tps? What are some thoughts on this? Weirdly, I don't have a set of feeler gauges and my snap on rep was out this week due to the holidays.
In the name of saving time and hassle, what about swapping my throttle body out for a jdm s5 turbo unit? I haven't dug it out of my parts stores yet, but I *think* the only difference is the twin tps? What are some thoughts on this? Weirdly, I don't have a set of feeler gauges and my snap on rep was out this week due to the holidays.
11-26-16, 12:24 PM
#9
Here's what I would do instead...
Remove the thermowax completely from the throttle linkage (sorry, I've deleted my wax and all it's linkage entirely, so I can't recall the "easy" way to do this). Essentially what you've done is remove the choke cable because cracking open the throttle plates is all the thermowax does.
You'll need to feather the throttle to get the car to warm up but once the water sensor sees 160°, the ECU will go into normal running mode and you can begin adjusting idle and tweaking out the hunting or decel issues- secure in the knowledge that none of the cold start mechanism is screwing with you.
After that you can decide if you need the thermowax at all...I didn't.
Remove the thermowax completely from the throttle linkage (sorry, I've deleted my wax and all it's linkage entirely, so I can't recall the "easy" way to do this). Essentially what you've done is remove the choke cable because cracking open the throttle plates is all the thermowax does.
You'll need to feather the throttle to get the car to warm up but once the water sensor sees 160°, the ECU will go into normal running mode and you can begin adjusting idle and tweaking out the hunting or decel issues- secure in the knowledge that none of the cold start mechanism is screwing with you.
After that you can decide if you need the thermowax at all...I didn't.
12-24-16, 12:00 PM
#10
It's been a while, I apologize...
I ended up making a crossover pipe to take place of the intercooler so that I could, with the engine running, determine what I should do based on what I've read and some of the input from you guys.
So here is what I have ultimately determined:
My thermowax has somehow managed to lose some of it's wax.. I can only assume this as I believe the position and movement of the piston is not what it used to be. This, I imagine, is why in my case I have to turn the adjustment screw to the point of nearly squashing the spring in order to get the pin aligned with the correct matching mark on the cam. In doing this (setting the marks where the should be), I could achieve the appropriate cold-start idle speed, barring the AWS system which has long since been removed from service. So, result... at a price. Once warmed up, the engine would idle so low that it would simply stall. It would *sort of* run, but be turning too slowly and resulting in a stall. To counteract this, I adjusted the fast idle screw. It's got an 8mm jam nut and a flat blade notch to adjust it. I'm reasonably certain this adjusts the 'home' position of the throttle plate giving you a 'base idle' as one member implied. So with the thermowax set, and the engine running and warmed up (albeit on the verge of stalling, which it did a few times until I got to the throttle body fast enough), I then adjusted this fast idle screw to bring the idle speed up to where it is supposed to be once warmed up. I verified the roller had separated from the cam with an inspection mirror and then began the process of adjusting the throttle position sensor to one volt, using the TPS harness for a ground and the Initial Set Coupler jumped (even though there is not a BAC plugged into the harness).
Results are good. Cold start idle speed is as it should be now, as is warm idle. It doesn't rev up massively between gear changes or hang on to the revs as it used to, but it's still not perfect...
I want to locate a good S4 TII BAC, because without the BAC valve and the engine warm, it wants to stall if you disengage the clutch and the revs plummet towards idle..it just sort of keeps plummeting and stalls. Not a huge issue if they're only coming down from 1300 or so, but anything about 2 - 2,500 revs and it'll die.
However, if I plug in the S4 N/A BAC that's installed onto the manifold now, when you first start the car it'll rev up once towards 2,800 and then immediately come back down to a reasonable speed. But, it also won't stall quite as easy when you disengage the clutch from a higher engine speed.
I'm also going to set the TPS again metering at the ECU because I'm certain that the wiring is not as healthy as it once was and there's probably a voltage drop of some kind. Call me obsessive.
Before anybody screams vacuum leak, I'm always checking for them because none of the standard vacuum hose available locally lasts that long in the heat, caps degrade quickly, so I'm end up just periodically replacing hoses and caps when they start so show the first signs of wear.
I ended up making a crossover pipe to take place of the intercooler so that I could, with the engine running, determine what I should do based on what I've read and some of the input from you guys.
So here is what I have ultimately determined:
My thermowax has somehow managed to lose some of it's wax.. I can only assume this as I believe the position and movement of the piston is not what it used to be. This, I imagine, is why in my case I have to turn the adjustment screw to the point of nearly squashing the spring in order to get the pin aligned with the correct matching mark on the cam. In doing this (setting the marks where the should be), I could achieve the appropriate cold-start idle speed, barring the AWS system which has long since been removed from service. So, result... at a price. Once warmed up, the engine would idle so low that it would simply stall. It would *sort of* run, but be turning too slowly and resulting in a stall. To counteract this, I adjusted the fast idle screw. It's got an 8mm jam nut and a flat blade notch to adjust it. I'm reasonably certain this adjusts the 'home' position of the throttle plate giving you a 'base idle' as one member implied. So with the thermowax set, and the engine running and warmed up (albeit on the verge of stalling, which it did a few times until I got to the throttle body fast enough), I then adjusted this fast idle screw to bring the idle speed up to where it is supposed to be once warmed up. I verified the roller had separated from the cam with an inspection mirror and then began the process of adjusting the throttle position sensor to one volt, using the TPS harness for a ground and the Initial Set Coupler jumped (even though there is not a BAC plugged into the harness).
Results are good. Cold start idle speed is as it should be now, as is warm idle. It doesn't rev up massively between gear changes or hang on to the revs as it used to, but it's still not perfect...
I want to locate a good S4 TII BAC, because without the BAC valve and the engine warm, it wants to stall if you disengage the clutch and the revs plummet towards idle..it just sort of keeps plummeting and stalls. Not a huge issue if they're only coming down from 1300 or so, but anything about 2 - 2,500 revs and it'll die.
However, if I plug in the S4 N/A BAC that's installed onto the manifold now, when you first start the car it'll rev up once towards 2,800 and then immediately come back down to a reasonable speed. But, it also won't stall quite as easy when you disengage the clutch from a higher engine speed.
I'm also going to set the TPS again metering at the ECU because I'm certain that the wiring is not as healthy as it once was and there's probably a voltage drop of some kind. Call me obsessive.
Before anybody screams vacuum leak, I'm always checking for them because none of the standard vacuum hose available locally lasts that long in the heat, caps degrade quickly, so I'm end up just periodically replacing hoses and caps when they start so show the first signs of wear.
12-24-16, 12:46 PM
#12
I had some corrosion of the nipples, and a little nastiness came out when I flushed and blew out what I could, but I'm actually fairly certain the flow of Coolant through the hoses and the thermowax is quite good.
I do agree with you though, the crud buildup is hugely common and is a problem. I swapped the tb/uim on my old na engine and the unit I replaced mine with was was so built up It looked like flow was nearly impossible.
I do agree with you though, the crud buildup is hugely common and is a problem. I swapped the tb/uim on my old na engine and the unit I replaced mine with was was so built up It looked like flow was nearly impossible.