scca28 said:
I also believe it could be the coolant temp sensor fror the computer. Anony91xj was right on with his description. I had the same problem on my other car, an Aerostar with the same symptoms. Running real rich,black smoke at the tail pipe and poor milage. When I finally checked the resistance of the temp sensor it was either completely open or closed, I don't remember which, but the new one had a readable resistance value. Popped that in and it kicked over on the first crank, no more smoke and milage went way up. Good luck with this.
Possible, sometimes they are not bad enough to trip the "Check Engine Light" but bad enough to cause problems. If my list is correct, either the MAP, the TPS (timing) or the engine temp. sensor should trip a constant "check engine light" if they are out of parameters.
I'd be tempted to look at something physical instead of a sensor. Stored computer codes, even intermittant codes (IMO) aren't to be relied on, but are an indicator, not difintive often enough..
Grounds and dirty connectors will mess with your sensor values, maybe not enough to trip a code, but wrong none the less.
The IAC is active mostly at throttle closed, but does keep right on doing fine air adjustments no matter what position the throttle plate is in.
Really poor ignition, will cause a fuel build up, that can make a motor run crappy. Anything from weak spark to bad fuel.
High (low) fuel pressure or a partially plugged return line (or in line/filter sock).
Things that would likely not throw a code, but cause the symtoms, are something to look at.
The IAC is fairly easy to service and probably needs it anyway, even if it's not the problem. Grounds need to be periodically checked anyway, connector cleaning is another (regular) service item after a certain age.
I know what my persent problem is, a plugged Cat. soon to be changed. My gas mileage has really gone south and the motor vacuum is way low at higher RPM's.