I have a 1990 t/a w/ 5.0L with some minor mods. I've had this idle issue for the entire six years I've owned this vehicle. When I bought the vehicle, it was idling high and overheating. I was able to figure out that something kept tell g the IAC to go wide open. I performed the idle reset procedure several times and it did change for a short period of time but would eventually go back to idling high and staying there. I found the TPS had a dead spot in the voltage range and changed the sensor. Performed the reset procedure, and it still went back to idling high. The car is by no means a daily driver and I don't work on it all the time. I've only put 5,000 miles on it in six years. I've been able to work around the idle issue by unplugging the IAC and setting the base idle. I'm confused as to why this does not set a check engine light. This is making me wonder if there is a problem with the computer. I'm looking to do some more serious mods this winter and really want this idle problem fixed before I go any further with the mods. Has anyone had this problem? Could it be caused by the computer or possibly the MAP sensor? I haven't checked vacuum @ the MAP sensor when this occurs, just a thought.
Idle problem
- Thread starter FBOMB
- Start date
I actually do have an OBD1 scanner. The MAP is the one thing I haven't thought to look @ when it's idling high. It was something I was thinking of the other day while brainstorming with a friend. What I was trying to figure out was, will a malfunctioning MAP sensor cause the computer to misinterpret the vacuum reading and tell the IAC to open. I do not have any vacuum leaks by the way. It doesn't actually happen all the time, but when it does, the idle will not come back down on it's own. I have to do the reset procedure again to get it to idle correctly. Something is telling the IAC to open all the way and I don't know if it's the computer or an input to the computer(MAP)?