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Car won't hold idle unless throttle is held open during cold start.

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Car won't hold idle unless throttle is held open during cold start.

Old 11-25-15, 05:26 PM
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Car won't hold idle unless throttle is held open during cold start.

I'm still learning alot with this computer, as far as start ups, I have problems with cold start and , Im not sure if its my tune or my grounds need work, the car will barely hold an idle when first started (500 rpm or so), and wants to stall out easily, and throttle transitions are very weird, car wants to choke out easily unless you ease onto the throttle just right and hold it to around 2000 rpm until its warm enough to stabilize on its own after you let off the throttle.

Also when I cut my villager fan on , if i use the high fan speed the idle drops quite a bit and car wants to stall out, which doesn't seem normal, is this probably grounds or more likely my tune , and the fact that i dont have a bac valve ? I am running an FD alternator and voltage stays around 14 with it on high after it stabilizes, but initially it seems there is a large voltage drop as its cut on even when the car is idling at around 900 rpm.

Car is running on maps based on MAP sensor, so the idle is the only thing that the tps sensor is used for.

Last edited by wthdidusay82; 11-25-15 at 05:34 PM.
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Old 11-28-15, 10:31 AM
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All engines need a higher idle speed, created by more aiflow and fuel, to run when they are cold. Due to poor atomization of fuel when the engine is cold. OEMs accomplish this by an idle (BAC) valve or in new vehicles, just opening the fly by wire throttle a bit. And the fuel map richens up the AFRs a little.

And even when warm, any additional load on the engine will want to pull the idle down which must be compensated for by additional air/fuel.

So yes, as you surmise, the lack of BAC is going to be the cause.

Certainly tuning is going to be part of the issue. As your tune is refined, you can refine the Water map to keep the AFRs at the most ideal. The Water map is a percentage of the load map, so adjusting it depends on having a load map that is reasonably well set up.

You will never get that nice stable cold idle on the car without a BAC valve.

Now that said, putting the thermowax and cold start cam back on your throttle body will help IMMENSLY. Because that nudges the throttle open a bit when cold, creating that idle up. And since it is purely mechanical, it works regardless of the fact that the Microtech is too stupid to control an idle valve.

That won't help your idle when warm of course. For that, see my comments in your timing thread. But a load is always going to pull it down a little.
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Old 11-29-15, 11:45 PM
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Car won't hold idle unless throttle is held open during cold start.

Pretty sure it was all removed by the previous owner (all cold start stuff), I have a s4 with a fd uim\tb. The micro tech was made for a fd so I'm going to put a modified trailing coil on with two igniters. I'm still waiting on that , hopefully it helps.

My tune also leans out in certain spots using the normal mode, I think I need to switch to matrix to fine tune the fuel table instead of basing it on just vacuum load.

I'm using map sensor for all the load map , tps is just for idle.
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Old 12-06-15, 10:02 AM
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The trailing coil probably won't make a huge improvement.

Choices are limited when you can't control the BAC. Either turn the idle up too high, or use the thermowax. FD thermowax assemblies shouldn't be too hard to find. I know I have several sets, but they are packed away in boxes from the move to my new shop and until I get everything sorted through I'd have no idea where.

Matrix will definitely give you much finer control. Normal tune is basically "carburetor" mode and as you know relies on a main fuel curve with corrections applied to it. Matrix will get you a 3D fuel table, poorly interpolated, but at least much more resolution.

Definitely don't switch to Alpha-N. Keep it set to speed density. Once tuned, you will probably find that the pump functions should be switched to TPS, not MAP.
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Old 12-06-15, 06:24 PM
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If you find those thermowax assemblies id buy one from you. Is there a good reason why people take them off? Im trying to get my car to function as best as possible for street use . My car starts when cold on e85 ive been playing w the crank map had to add alot of fuel in the colder temps. Runs like crap for about ten seconds then smooths out. I think it would be better on reg pump gas. Would the thermowax wax help out .
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Old 12-08-15, 12:15 PM
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What do you mean by alpha n?

Originally Posted by Aaron Cake View Post
The trailing coil probably won't make a huge improvement.

Choices are limited when you can't control the BAC. Either turn the idle up too high, or use the thermowax. FD thermowax assemblies shouldn't be too hard to find. I know I have several sets, but they are packed away in boxes from the move to my new shop and until I get everything sorted through I'd have no idea where.

Matrix will definitely give you much finer control. Normal tune is basically "carburetor" mode and as you know relies on a main fuel curve with corrections applied to it. Matrix will get you a 3D fuel table, poorly interpolated, but at least much more resolution.

Definitely don't switch to Alpha-N. Keep it set to speed density. Once tuned, you will probably find that the pump functions should be switched to TPS, not MAP.
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Old 12-12-15, 10:10 AM
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Originally Posted by johnrx2 View Post
If you find those thermowax assemblies id buy one from you. Is there a good reason why people take them off? Im trying to get my car to function as best as possible for street use . My car starts when cold on e85 ive been playing w the crank map had to add alot of fuel in the colder temps. Runs like crap for about ten seconds then smooths out. I think it would be better on reg pump gas. Would the thermowax wax help out .
I'll see if I can find them. Much of that "misc" stuff is in a large ******* crate which became the catch all box for the move. Currently sitting in front of the Cosmo, with also a desk and shelving unit on top of it.

There is no good reason to remove the thermowax assembly. People do it under the excuse of "cleaning" the engine bay or other such silly reasons.

The reason the thermowax exists is to mechanically raise the idle when the engine is cold in order to allow it to run smoothly, light off the cats and warm up quickly. Definitely it would help your issue.

Frankly it doesn't help that the Microtech afterstart enrichment seems to end SUDDENLY after about 10 seconds, instantly leaning the engine out and now making enrichment rely on the warmup map. Very stupid. Any other ECU allows you to adjust the duration and amount of afterstart.

Originally Posted by wthdidusay82 View Post
What do you mean by alpha n?
Alpha-N is the method of fuel calculation where the ECU uses TPS position and RPM to calculate the position in the load map, not RPM and MAP. Useful for engines that don't have a very good vacuum signal.
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Old 12-13-15, 02:27 AM
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I believe I removed my thermowax, maybe I can put it back on if I still have the assembly , would the port for it goto the nipple on the rear iron I assume ? Not sure where else I could get a feed.

I will look into switching pump settings to vary under tps changes rather then map, this is possible ?? I have to read the manual more.

Car definitely starts up funny, as it revsnit chokes until it hits a certain rpm where it smooths out.

I'll be working on everything as soon as I get my trailing coil setup installed which should be in the next few days.
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Old 12-13-15, 10:08 AM
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The thermowax connects between the port on the rear housing and the port on the water pump housing.

Swapping the accell pump settings to TPS is easy. I believe setting the Pump(number)Stop function of "OFF".
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Old 12-13-15, 01:14 PM
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Car won't hold idle unless throttle is held open during cold start.

My port on the back of the water pump was removed and has a sending unit for a water temp gauge in it that I tapped , for more accurate temp readings on my in car temp gauge.

Would it be safe to connect the rear iron port to it or does it need a way to loop back to the engine ? Seems like it would only be flowing one way like that and have no way to go back to the engine >. <

If that's the case I would need to make a Y split off the barb on the rear iron wouldn't I.
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Old 12-16-15, 09:14 AM
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The thermowax needs coolant flow, so it needs both ports. Perhaps you could install a T on the rear iron.
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