Collection of interesting cold idle behaviors, searched.
 

First off, the car is an S5, 90 gtu. Collection of idle related quirks that I am trying to track down. The AWS rarely works, (maybe 14% of every startup will it shoot the idle up to 3,000.) The car starts up normally, no long cranking, etc. once running, it will idle at or around where it should when cold for about ten seconds.

At this time, the car starts idle hunting. Idle raises, drops, raises, drops, rinse repeat. (also during this time the car starts smoking ridiculously bad, enough I cant keep it running for fear of the neighbors getting irate.)

Once the car actually warms up however, it idles fine and doesnt smoke the place out, the excessive smoking is directly linked to the surging idle, which only happens when cold.

So, i'm thinking, okay, BAC, Thermowax, TPS. check those.

I noticed if when the car is started, if i grab the throttle body linkage where the cable connects, and push it towards the passengers side of the car, which I believe is against the thermowax plunger, the idle does lower a bit.


I'm thinking the thermowax might be the culprit?

Also, I've set the tps, (although significantly long ago) using the ohms method, I believe the FSM says between 800 and 1200? I set mine to 1,000, after the engine was fully warmed up for at least half and hour, turned motor off, unplugged tps, measured at those connectors, and turned screw until it read 1,000.

My other question is, i keep reading about setting it using a volt method, is there any real difference?

Mostly just food for thought, Anyone have any advice to chime in?

The thermowax is your primary cold start device (out of curiosity, how cold does it get in Orlando?), so you need to get it set up first.
Believe it or not, this is most easily done by pulling the throttle body off the car.
With the whole thing sitting on a bench, you can easily see/access the linkages and by adding cold or hot water to the thermowax, you can see how it responds, making adjustments as necessary. Make sure the thermowax body and the coolant hoses are free or crud and flow well...the system is entirely dependent on good flow.

There really isn't any BAC adjustment- it either works or it doesn't and far as I know, it shouldn't be involved with cold starts anyway.

I ohm out the TPS to check for dead spots in the sweeps but use the volt method to set it.
I've added a permanent pigtail to the connector that my DMM probe fits into, so I need not "backprobe" it every time. Be sure to ground the initial set coupler during the adjustment.

The ECU sees volts and not ohms. Might be wrong, but the TPS is mainly used when the car has fully warmed up.

The smoke you have is likely a flooded engine or coolant.

The cold start high rev is based on the coolant/engine temp. Warmer weather should cause it to occur on a cold start. Colder weather it would not engage the system.

The engine does not like cold weather thus if one of many variables are out of sync then you get your problem. At least your's stops when it warms up.

Something might be causing the ignition timing to advance and retard over and over causing your symptoms.

AWS: this only turns on in a certain temperature range. if its too cold, it doesn't turn on, and if the car is warmed up it won't turn on either. specifics are in the FSM.

Thermowax: its just a wax pellet that pushes the throttle open when the car is cold. since its at the top of the cooling system, its typical for these to be full of crud/air locked, and it won't work right that way. secondly it is adjustable both for how long it is on, and how high the idle goes. i'd suggest cleaning out the hoses going to it, and then adjust as needed. t should be off by the time the temp needle is at the low line, which is 65c. again more specifics are in the FSM

TPS; needs to be set at idle, and the engine needs to be fully warmed up. the thermowax, as you recall pushes the throttle open, which effects the throttle position. i use the factory two light method, as it is measuring the OUTPUT of the ecu, and not the input like the other ways. its also easier and requires no thinking, you just turn a screw until one light is on. the TPS test plug has 3 pins, the center is power and the other two are grounds, so you can easily make a little tester out of LED's or whatever you feel like.

Idle speed: the S5 ecu is smart enough to have a target idle speed range and it has a limited ability to bring the idle up or down as required. the problem is that if you are too far out of its range, it will hunt for the right rpm and fail, which is a surging idle. idle speed, which again needs to be set hot, needs to be set to the right RPM, which i think is 750, but FSM would tell you this too.

FSM's are here Foxed.ca - Mazda RX-7 Manuals

if everything is a little out of adjustment it can run pretty lousy, if it was my car i'd clean out the thermowax, warm it up, adjust the idle speed, and then set the TPS. i'd pull codes too, there are some that don't turn the light on

By setting the idle speed are you meaning via the screw on the top of the TB? I need to do a quick search and pull up the volt method for the TPS. Currently it has no codes, but I believe you when you say it might have codes listed without throwing a CEL, so I will look there also.

As for cleaning out the thermowax, what i'm worried about is I dont have a JIS phillips, and the last time i slightly attempted, the screws wouldnt budge, so in lieu of stripping them, I let it be. As far as cleaning out the coolant passages for it goes, any recommendations?

Soak the screws with Deep Creep and then use an impact driver...those screws will loosen up.

Probably.

It's worth trying because dollars to doughnuts you'll find sandy residue in the thermowax body.

Anyway, you want to start with the gross adjustments first, then move to the finer ones.
At cold start there are two strategies being employed, one electronic and one mechanical. They are codependent for success.
First is the ECU which is primarily using the thermosensor (on the back of the waterpump housing) to know that the engine is cold. It defaults to a cold start enrichment map which totally assumes that the thermowax is doing it's thing and cracking open the throttle plates. The ECU has no way of actually confirming this is true but can only act as if it is until the thermosensor tells it the coolant has warmed up.
During this process, the BAC and TPS are basically irrelevant.

You'll also need to check the primary throttle plate idle gap. The primaries are never fully closed, the amount they are open at rest is in the FSM. Assuming no vac leaks, just these two adjustments (thermowax and primaries) should give you a steady idle from a cold start condition.

yep!

take the hoses off and blow through there, the hoses get gunked up too

Well, went and put the throttle body back on the car. While it was out I changed the thermosensor behind the waterpump, Changed out the vacc hoses on the TB, hosed the thermowax insides with degreaser and flushed with air/water, reinstalled. After startup, Same problem! (couldnt get the actual thermowax off the TB, screws are stripped.)

The car starts, then after about 20 seconds of running it will start hunting for the idle (idle surge) repeatedly. Does this cold or warm actually.

I noticed if i put pressure on the linkage, the idle drops a good amount. So i wedged a screwdriver against it to check to see what the idle rested at, here are the results:

https://cimg3.ibsrv.net/gimg/www.rx7...c9d4492bd7.jpg


Wedging the screwdriver against the intake pipe and linkage lowers the idle an audible amount.


https://cimg4.ibsrv.net/gimg/www.rx7...0d9dea5535.jpg


This is roughly what I end up with, and no surging.

I adjusted the throttle cable a bit, one way or the other too much and it starts hunting for the idle again. I got it to the point where it wouldnt surge or bounce. However, if i apply pressure to the linkage where I had the screwdriver wedged in, the idle still drops, although significantly less now that ive done the throttle cable adjustment.

I'm thinking of just replacing the entire TB to be honest. The car was originally an Auto, so the TB has the extra two vacuum bungs on it that arent needed anymore, and with the thermowax screws being stripped, I figured all the more reason to throw a five speed TB on there.

I know this sounds stupid, but I looked up on the FSM how to adjust the cable. It shows to adjust the nut closest to the drivers side of the car on the cable/bracket. (I think its labeled nut A on in the FSM.) Just to make sure I'm not an idiot, can someone please explain to me how to more thoroughly loosen the throttle cable? when i tried the entire cable itself was just rotating with the nut, not the nut itself.

Do i need to hold a wrench on the other nut on the passengers side of the bracket to keep the cable itself from turning?


Also worth mentioning, as i'm going over the FSM, it mentions the Primary and Secondary throttle valves on the TB. But it doesn't really specify which is which. as the TB sits on the car, as we all know there are three circular valves which open with the throttle. Two up top, one on bottom, like an inverted triangle.

My question is, which is the primary and which is the secondary? I would think that the singular one on the bottom is the primary, and the two up top are the secondary throttle valve, is this correct? I ask because the two up to have some minor play and are open when the throttle body is at rest, and can be force closed by adding pressure to them. I assume these are supposed to be closed at rest? I dont see any procedure for adjusting them closed in the manual though.

in short, yes. the cable is held on to the bracket by the rubber thing, and the two nuts. the two nuts need to be tight, but they can be moved to adjust the cable as needed.

with the car warmed up, there should be some slack in the cable. this is so when the thermowax is on, it doesn't get too tight.


that is correct, the single one at the bottom is the primary. the secondary side is on top. there are two sets of throttle plates on the secondary side, one is vacuum operated, and get pulled almost closed when the car is cold. the second set open with the throttle.

think of it like the BMW m5, where they limit power and rpm when the car is cold, its just analog

I'm wondering what the culprit is then, causing the idle to drop when i apply pressure to the linkage. The secondary plates that would be closest to the passengers side of the car (with TB on car, of course) have that play as I mentioned, but could they possibly be out of adjustment causing the idle to raise and the ECU to start 'hunting' thus causing the bouncing idle? you said one is vacuum operated, and pulled closed when car is cold, Maybe the play is normal because the throttle plates in question here are the ones that are closed when there is a vacuum and im barking up the wrong tree on that.

But either way, adding pressure to the linkage, causes the idle to drop, so something has to be out of adjustment. I might just swap out the entire throttle body for a Manual Transmission one like I said earlier. Seeing as how most of the AT crap on the throttle body I have shouldnt be needed anymore, seeing as how the automatic components have been long gone.

Apparently this S5 ecu is really picky, the second I let the idle get too far out of adjustment, it just hunts and goes nuts.

How many hoses run to the double throttle diaphragm on your car? If it's two then check the FSM to see how it operates and locate the vacuum hose which places vacuum to the diaphragm when the engine is cold and place vacuum on that hose and see if it changes anything.

I managed to find a pretty good deal on a S5 Manual transmisison TB, the salvage yard sent me the below photos in advance. I would bother with the TB on my car now, but its an auto TB like I mentioned earlier, and the car has been swapped to five speed, so I might as well put the correct TB on to begin with.

My memory could be off, but, with the throttle at rest, no pressure on the linkage, should the valves be sitting like they are? primary closed, two up top open, and the two behind those closed? Is this normal?

Pics:


https://cimg3.ibsrv.net/gimg/www.rx7...6bdbf4330e.jpg


Manifold side







https://cimg4.ibsrv.net/gimg/www.rx7...510f8fbd97.jpg


Side of TB that intake elbow bolts to

Look normal for a healthy 5 speed S5 TB? I would say so but the position of the valves has me wondering, I can't remember what mine looked like when I had it off the car. :lol: Any clarification on the TB valves would be helpful (are they in the right positions in the pictures for the linkage being at rest?)

AT throttle body at rest. Note how the front two valves up top are closed...and on the five speed they are open. any clarification?



https://cimg9.ibsrv.net/gimg/www.rx7...2423618e73.jpg

Makes sense that they would be open at rest on the MT TB. When the car is cold, there is vacuum to the double throttle diaphragm, which should shut them closed.

It makes sense, I'm just making sure the TB I'm about to buy isnt broken. Why would the front plates be closed on the A/T throttle body, but open on the MT?

Because I believe the diaphragm works differently for the auto as compared to the manual version the difference.

The FSM shows a much more complex vacuum line setup on the AT TB compared to the MT

https://cimg3.ibsrv.net/gimg/www.rx7...77c266eced.png


You couldnt be more correct about that.

The Vacc system has two less hoses and one less check valve.

https://cimg4.ibsrv.net/gimg/www.rx7...f157ccc8e1.jpg


MT Throttle body installed.


Car started up like it normally does, then after about thirty seconds, again proceeded to fumigate the neighborhood. Drove it around until it warmed up, set the idle via the screw on the top of the TB, and it was idling fine after that. (note, I also have the hose missing for the brake booster vac line, I need to source a replacement, and that is probably a huge chunk of why the idle is wonky.)

It's a notable improvement over the auto one though, I don't have to apply pressure to the linkage to keep the idle from roaming anymore. Tomorrow i'll probably attempt to source a hose from advance that connects the brake booster hard line from the engine to the firewall that doesn't kink, and calibrate the TPS.

At this point things are getting narrowed down. Thermoswitch is brand new, all the vac lines on the TB are replaced. MT throttle body on there, idle screw set. No more roaming idle all the time though, so thats progress. Edit: also, the junkyard I bought it from charged me 25.00 for the TB, 30 to ship it, so 55.00 total, but I scored the TPS with it as well, so I feel I got my monies worth.

Started her up again today. Cold idle is a bit weird, goes up to about 2k- 2.5k, attempting to rev it will not lower the idle. As the car idles the rpms move fractionally up and down (no idle hunting like it was doing before). Then after the thermostat is fully open for a few seconds to a minute, the idle just drastically drops and settles to where it should, and driving it, etc after this point, it settles normally. (at least when I tested it.)

So, if the Thermoswitch has been replaced, brand new, thats out. the TB is hooked up properly, in regards to the vacc lines according to the fsm.

Are the front two secondary valves supposed to be pulled closed by vacc when the car is cold? I have the vac lines connected, and I know the back two primaries are always closed at rest, but I can actually move the linkage manually for those front two plates that are connected to that vacc diaphragm when the car is cold or hot (doesn't change the idle when I do this, but it just has me concerned)

I'm following this with interest as my '90 GTU has a similar behavior... Idles normal when i first start it, and then the idle starts to surge after a minute or so, but doesn't smoke like Tyblat's. I usually start driving it once the idle starts surging. Once it is close to warmed up, the idle surges when it is in gear with the clutch in sitting at a light, but if I put it in neutral it holds steady. Once it is good and warmed up, then it idles perfectly. I've mostly just chalked it up to just being a quirky old rotary, but it would be nice to fix.

Check the clutch switch pin at the ECU and compare it according to spec as specified in the FSM. Also, check the BAC.

I was under the impression the only two things that regulate the idle condition from cold (with no accessories on) start is just the thermosensor and thermowax for an S5.

Could my BAC be contributing to my odd idle behavior?

yes, they are supposed to closed when the car is cold. they get pulled closed by vacuum.

If it where me (and I already did) I'd get rid of the secondary throttle dummy plates.

The reason I call them dummy plates is because their sole purpose is to keep you from beating the snot out of the car when it is cold. If you are not a dummy, you don't need the dummy plates to work. You can cap off the vac lines for it and leave the actuator as its spring will keep them open. One less thing to worry about.

I removed that system on my car because the diaphram in the actuator was busted causing a vacuum leak, which caused my idle to hunt. I left the actuator there just to hold the dummy plates open.

My car is an S5 NA M/T with cruise so it made it easy. I just had to delete the "Tee" vacuum line from the thermal vacuum valve and just run a vacuum line straight to the cruise control and completely disabled the system. All I have left is the actuator to hold the plates open and the thermal valve sitting there disconnected to plug the coolant hole.

Very interesting. Thanks for chiming in about those secondary valves. So if i'm understanding you right, the spring keeps them open, and vacc pulls them closed. Naturally at idle they are open. So thats why when looking at the car running after I put the MT TB on, I could just open and close those by moving the actuator with my hand and have absolutely no change in idle?

Since you mentioned they are there to keep you from beating the car up when its cold, I take it when the car is cold, if I tried to drive it like a moron, the vacuum would kick in and pull those valves closed?

So I guess in a shortened sense, my question is, at cold/warm idle, even when hooked up properly, those dummy valves are supposed to be open...right? And they would close via vacuum if i tried to beat on it when cold?

Under normal operation, they would be shut when the car is cold. The thermovalve allows vacuum to shut them when cold and closes off vacuum when warm to allow them to be open.

Cold = closed

Warm = open

It's just there to keep you from molesting the car when cold, you don't need it. If you have proper control of your right foot and have a brain, you don't need it.