I have a 1987 Iroc with a 5.7 Tuned Port Injection and a 700r4 transmission. The car idles fine when it's cold and I can drive it for about a mile before it warms up and acts erratic. The rpm's move from 500 to 1000 and the engine runs rough. When it does this, I can shut the engine off and restart it and it will idle fine. Then I'll drive the car down the parking lot about 150 feet and the car will idle rough again. If I restart the car and just let it idle without touching the gas, it will idle prefect and sound normal indefinitely. My second problem which I'm not sure if they are related, is my cooling fans don't work. Neither A/C or engine coolant sensor switch. I installed a new switch on the cylinder head and bypassed it to check the circuit, it still didn't turn the fan on. I also bypassed the A/C switch and it didn't turn that fan on either. I temporarily installed a bypass switch through the ground wire in each of the two relays. Is there a third relay or do I have a computer issue? Can anyone help me with either of these two problems!

 

I fixed the fan problem! I replaced the relay on the firewall with another one I had in the shop. I still have the idle problem. I reset the TPS at .650 ohms and checked the timing again. Still does the same thing when I drive it.

 

are you sensors actually working correctly? if you have acess to a MODIS hook it up to your car and see whats going on with the TPS and other sensors

 

Unfortunately, I don't have acess to that equipment. There is no check engine light on when the car runs poorly. I was thinking it might be the transmission speed sensor. Any thoughts on that idea?

 

Does it run rich or have a smell as if it is? Possibly a Coolant Temp. Sensor? If the ECU thinks it's -40 degrees outside, it could affect the fuel delivery and possibly cause an idle issue. Long shot I know. The whole runs ok for a bit after you restart it though is probably just because it is running in closed loop on a set computer strategy for a set number of seconds before realizing it is warm and running in open loop. Once in open loop, it is reading sensors for data and fuel strategy and one of those sensors is probably the issue.

 

you got it the wrong way around... open loop is when first started, closed loop is at operating temp.

 

I put the car up on jack stands yesterday to see if it would do it with the tires free wheeling. Sure enough, once I put it in drive and give it some gas and let off, the rough idle comes back. Otherwise if I don't touch the gas in gear, I can idle the car all the way up to 230 when the fans come on. Yeah, that's another thing, way does GM set these tempatures switches so high? Can they be lowered somehow in a correct manner? Maybe a lower temp switch?

 

My bad...brain fade there...dyslexia kicking in again. Thanks.

 

I borrowed a Snap on scanner yesterday. I get one constant code for fuel pump voltage to low or high, but it only reads .1 volt lower. The only thing I see that changes when I drive the car is the Idle Air Control doesn't drop back to 50 (mV) it bounces around 85 (mV) and runs rough. Do you thinks it a bad IAC?

 

Could this problem be from the 24lb injectors I installed with the new motor at 10 to 1 compression?

 

Thanks for you guys awesome input! I figured it out on my own !

 

what was the solution to the problem?

 

The EGR valve was no good.

 

How did you determine that the EGR was bad? I've been having similar problems.

Thanks