Idle Problem. Please Help
 

My Jza80 TT wont start in the morning unlless I have my foot on the throttle. When it warms up then it will idle at 500pm. It seems like the Idle control valve does not take any commands from the Ecu. Please give me a few guidelines, suggestions on where to look for the problem. Thanks

Do you have a copy of the TSRMs? I'm sure there's a troubleshooting section for the IACV. Imo, the TSRMs are a 'must-have' for all Mkiv Supra TT owners that want to do their own maintenance and modifications.

My car is Jap Specs and Jap Import. I have nothing. My michanic is unable to locate the problem and my only way is to sort out my self with the help of you guys. :(

In that case, troubleshooting will be more difficult. As a first step, I'd suggest finding another Supra owner that lives near you to see if they'd let you swap their IACV temporarily. If that fixes the problem, all you need is a new IACV from Toyota...

have you tried running a diagnostic?

It may be your IACV(idle air control valve), but is there a problem with idling once the car is warm?

I know you said it idles when it is warm at 500rpm but do you notice any flutering at all? Anything different? Is it at all slugish?

Its just kind of odd how the IACV works fine once you are warm but during cold start it doesnt seem to work.

Do you notice any wires loose? Did you have any electrical problems before? I would try changing the IACV first then if that doesnt solve the problem we can trouble shoot some more.

Is there an echo in here?

we won't really know much until he does at least a diagnostic... it very well may be the isc but pulling codes is always a good first step

Agreed...if your Supra's ecu has any codes, it's always a worthwhile exercise to go through them first. Although you didn't mention the check-engine light, please post any codes stored in your ecu and we'll help you make sense of them.

I have replaced the IACV a second hand one from a friend but no luck. Ive also checked the Air intake sensor & coolant and the ok also. Done many ecu resets but still no luck

Yes I did, no codes at all and everything looks ok. The IACV reads 125 and stays there no matter what happens, regarding water temp and revs. It looks like it does not get any commands from Ecu

Have you checked for boost/vacuum leaks? If a boost/vaccum leak exists around the intake plenum area, it can (inappropriately) function as a secondary IACV. If your Supra uses a maf, this additional unmetered air will cause an over-lean condition at idle.

Also note that some boost leaks, especially ones in the intercooler piping, can partially seal up when hot, due to expansion of the couplings, clamps or intercooler pipes.

When it gets warm the revs raise up to 1500. It starts cool with no revs and rises all the way up to 1500 when its realy hot.

I had no problems with electrical in the past. No wires loose, as far as the diagnostics reads. The idle reading is stack to 125.

No check-engine light. Sometimes a sensor might be sending wrong data but not be dead so that the check-engine will go on. I have done some checks on readings given by air and coolant sensors but they look ok. Just to make sure i have replaced these as well.

This is the only thing I have not checked 100%. It might be a cracked hose. I have to spend a few hours searching for leaks and this what I am planning to do asap. Do you have any idea about the sensors that have effect on the way IACV works?. There is also a vaccum hose connecting the intake plenum with the throttle, do you have any idea what it does ?. Cant find if there is a crack on it. I will get some Samco Vaccum hose and replaced as may as I can. This might help.

The best way to check for boost leaks is to pressurize your entire charge-air system with an air compressor (up to about 30 or 40psi - if it can handle 40psi cold, then 20psi or so hot should be no problem). With 40psi of air in your charge-air system, you should be able to hear any/all boost leaks loud and clear.

thanks very much , i can do this . I have an air compressor and im looking forward to tomorrow morning to do my tests. That's clever , never thought of it..Many thanks and i ll keep you informed.