earlpote

hey guys,

so i recently installed south bay injectors in my car and fixed the stalling when slowing down/coming to a stop problem. but now ive got a new one. if i start the car when its cold, itll run for a second then die out, unless i hold on the gas for a little bit then let off, itll roughly idle til its warmed up then it runs fine. only other thing i did other than injectors is put a polished plenum and holley avenger throttle body on it. i have the idle adjustment screw all the way out, and even with that it only idles at 600 when warmed up (which i hear is good) TPS sits at .54 volts at idle. it has a new IAC valve.

any suggestions? thanks

earlpote

1989 GTA w/ 350 TPI

lonestar7

iTrader: (1)

I'd check the coolant temp. sensor connector and resistance readings. Also check for vacuum leaks.

Bob88GTA

iTrader: (2)

Earl,Follow these link's to a T

https://www.thirdgen.org/forums/post...702-post5.html

or this one

https://www.thirdgen.org/newdesign/tech/tpimod2.shtml

earlpote

i did the minimum air adjustment a few days ago with no luck, following that second link.

and how would i go about testing the coolant temp sensor? are you talking about the one obn the front of the intake manifold? what ohms should it read?

thanks

Bob88GTA

iTrader: (2)

Here ya go, and yes on the location

greenyone

iTrader: (1)

Try the old propane around the intake trick to see if you have a vacuum leak.

miamivice

I am following this post, have the same problem on my car....

earlpote

exactly how do i go about testing the coolant temp sensor? obviously using a multimeter, and plugged in with engine running, but what wires need to be probed?

also, i tried spraying around the intake with carb cleaner with no luck... i dont see how it could really be a vacuum issue anyway, because it runs great when warmed up.

it idles at 500 rpm at startup and stays about the same or maybe 550 when warm. so im assuming the issue has to be something to do with some type os sensor that regulates the idle when cold?

earlpote

anyone?

88Camiroc

I can say i don't see how at all how the coolant temp sensor will affect the issue you have. All it does it when the temp sensor senses a certain temp it tells the computer to turn the fan on. Have you checked your fuel pressure? Have you changed your fuel filter lately? The reason i say that is because when the car is warm it doesn't need a higher demand for fuel. At a cold start your car idles higher to warm up so it needs more fuel. I would check your fuel pressure.

lonestar7

iTrader: (1)

There is sometimes confusion concerning the fan switch and the CTS. The temp sensor that control the fans is located (on Most L98s) toward the back of the block on the passengers side and is not used by the ECM for engine temp data. The CTS is located on front of the engine below the intake plenum. The CTS sends engine temp info to the ECM used to calculate the air/fuel ratio, so if it's sending bad data to the ECM, it can effect idle by not making the mixture rich enough when the engine starts up cold. It can also fail in a way that will make the engine run rich at normal operation temps.

Street Lethal

iTrader: (16)

Your wasting your time without datalogging, and forget about TPS volts, what matters is where your steps are. The ECM will control your idle RPM, and all the fast idle screw will do is either make it easier, or harder, for it to do so. They come "capped" from the factory because they are preset based on what the engine came with, but the slightest change in VE due to added or modified parts will effect where the adjustment screw needs to essentially be. With your adjustment screw all the way out, your idle air is solely relying on the IAC passageway to maintain incoming air for it to idle (based on your engine's demands), and with 600-RPM being the target idle RPM, your simply not getting enough air in to allow for the ECM to regulate correctly, and she is running rough and/or stalling as the byproduct. Now, turn the adjustment screw back in during idle just until your idle rises above the 600-RPM mark and is not able to come back down, as this will tell you the ECM cannot correct for it, then "slightly" back it out some more until 600-RPM is again realized and the ECM can resume control, but this time it will be able to control from both sides of the spectrum, meaning it provides room for the pintle to correct from both perspectives; too much or too little...

88Camiroc

street lethal you think it has nothing to do with the fuel pressure? not second guessing you by any means Just trying to learn something new. I know that he mentioned about the idle adjustment screws but i guess that i didn't think anything about that.

88Camiroc

earlpote if it was a sensor then 9 times out of 10 it will throw a check engine light. not always the case but it will most of the time.

earlpote

yesterday my radiator drain plug started leaking on me, so now that the coolant is flushed out im just going to replace the coolant temp sensor while i can, its a pretty cheap part anyway. ill let yall know if it helped any.thanks

earlpote

Replaced coolant temp sensor yesterday, tested the old one and it was fine but just replaced it anyway since the part is cheap and I had the chance to anyway. didn't make a difference.

ill check fuel pressure today, last time I checked it was good, on the low side of the normal scale, but still good.

earlpote

also ran seafoam through vacuum hose yesterday, and smoke was coming out from the passenger rear side of the engine, couldn't tell exactly where it was. car has edelbrock headers. probably have an exhaust leak at the header?

Fred SS

iTrader: (3)

Any updates to this thread?

Reid Fleming

iTrader: (2)

Some things to add to the conversation. Before you try to adjust the min idle screw, you must take the throttle body off, take the IAC off, and spray the heck out of the throttle body with carb cleaner. Take the springs out of the IAC and spray them too. Open the butterfly valves and spray both sides. I guarantee that if you haven't done this in the last 3 years that mountains of black gunk will come out. Let it dry for a few hours and put back together. Just visually looking a the throttle body with the intake hose taken off won't show you any dirt. The black stuff hides inside the passageways and in the spring of the IAC.

There is no way the min idle screw should be all the way out or all the way in. This means that the IAC is either fully closed (your throttle body is too far open) or your IAC is all the way open (your throttle body is too far closed). Either way gives you little or no adjustment. And that's the whole idea of the IAC. It can go either direction.

When it comes to actually setting the min idle screw, the advice in the links above does work. But I use an easier way myself. With WinALDL and a laptop, I fire up the car and take it for a long drive. Get the coolant temperature all the way to operating temp (about 200-220°). At that point, I'll drive home and adjust the min idle screw until my IAC "counts" are in the 30-50 range with the car idling in PARK. Closer to 30 is better. But anywhere in the 30-50 range should be good. (I got this advice from PCMForLess's website.)

The IAC counts will read differently in DRIVE with the car stopped. So only make decisions on this based on the PARK reading.

Having the IAC reading 30-50 in PARK at full operating temp means that it's still adjusting itself to be open slightly when the car is warmed up. It gives it still some ability to adjust if you get stuck in rush hour traffic jam (let's say coolant temp spikes to 230-240°) And it gives it a large window of adjustability when the car is cold in the morning. An IAC that is fully open during a cold start in the morning would read 160 counts.

WinALDL also easily allows you to set the TPS voltage when you're done. But do that last. As changing the min idle screw will change the TPS at the same time.

Reid Fleming

iTrader: (2)

Pardon me, I didn't see you have a new throttle body in the original post.

In that regard I'd say check three things.

1) Vacuum leak. How much vacuum are you pulling at idle?
2) Have you cleaned the Mass Airflow sensor? CRC makes a Mass Airflow spray cleaner.
3) What is your base timing set for? Should be 6° BTC stock.

Fred SS

iTrader: (3)

Reid, that is some good info. I hope it helps Earlpote. I'm having the same problem as him. I have TurnerPro RT, even though it is picky about connecting to the ECM, I'm gonna try what you suggested.

Earlpote, you still have the problem?