i have a 89' IROC 350 TPI and am having probs with idle. it's all stock with new MAT Sensor, MAF Sensor, Plugs, Wires, Rotor, Cap, Temp Sensor, TPS Sensor, and O2 Sensor. i have adjusted the idle air and tps. at this point it idles around 500RPM. once i connect the IAC and start it up the idle will jump to 1000 and stay there. i have no idea what to do next. The other problem i am having is with the primary engine cooling fan. it is always on. i have replaced the fan switch and still the problem persists. i could use any suggestions. i don't know if the two problems are related? i get no trouble codes. thanks for any help.

 

- Check for any vacuum leaks
- Sticking Throttle cable

Also does your idle stay at 1000 RPM all the time or it goes down to 750 when parked/waiting at the lights?

I notice my car would do the same thing when I disconnect/connec the battery. But after a while I guess it learns and idle drops to 700 RPM

 

I find a lot of people here try to adjust the idle speed with the screw, just liek the old style carb setups... you can not do this, there is a set range that the IAC must work at... have the dealer, or a reliable mechanic with proper diagnostic equipment, set the idle speed. As for the fan, are you sure you replaced the proper sensor? Ther are 2 temp sensors. Have you checked for trouble codes?

 

the idle stays around 1000 in park and it does not go down (unless put in gear). Idle air has been adjusted per tech articles instructions (method worked on my 88' perfectly). as mentioned already no trouble codes. yes i know the difference between the two swtiches(gauge one, fan switch located on pass side head between #6#8 plugs). i have a stehoscope and have checked around runners for vacuum leaks but found none. i will look elsewhere for vacuum leaks. thanks for the reply's

 

The Primary fan is controlled by the ECM. ECM gets input from the CTS located at the front of the intake, then according to CTS info, turns fan on and off.

Idle speed is also dependant on CTS info...could be a relationship with the CTS???

I don't think it's a vacuum leak, or you'd have high idle with the IAC disconnected too.

My feeling is the IAC is not controlling properly, or that it's not being told the correct info.

I had a similar problem under warranty many years ago, dealership replaced the ECM and the IAC valve (least that was what was on the service report) to sure the problem.

 

i have replaced the cts. well i too was thinking something towards the ECM/IAC being the culprit. i will replace the IAC first and see if that helps. the next thing i will attempt is changing out the ecm and see if that helps. if not i will be back for some more good input. thanks guys.

 

well guys i have replaced the IAC valve and it still idles high @1000 RPM. I have the problem with the primary engine fan that never turns off. i guess i'll have to try the ECM tomorrow.

 

well guys i have replaced the IAC valve and the idle problem persists. i found a minor vauum leak and have fixed. the problem still exists. i will replace the ECM tomorrow and see if the idle problem, fan problem, and 30MPH lockup go away. any suggestions???

 

read responses, beofre you try expensive part check to see if car is running in open loop. to do this put car in field service mode. with engine running(fuel inj models only) put in jumper as you would to retrieve codes(term A+B ALDL conn.) and look to see flash rate of MIL lamp. if in open loop it will flash rapidly, in closed loop light will slow down to one flash per second. did you properly adjust TPS as per book. since fan is running, are you sure coolant temp sensor is correct one and working. i would start at the beginning and recheck all work. lot of stuff replaced! high idle also possibly oxy. sens not responding. work on a lot of electrical probs. with modern cars and have found the ECM the culprit in very few cases. as was said before by someone on the board also check for trouble codes.

 

ttt

 

well guys i have found the culprit to all my problems. the ECM/PROM. well i replaced it and the fans and the idle now work as they should. this is for reference just in case some of you guys are having the same problems. well thanks for your help.....

 

Nothing to add, just wanted to thank you for posting a follow up after you found the solution. So many times people don't do that, thus leaving a post open ended, making it harder to learn from.