idle air control

[bigred91]

I have a 1991 k1500 5.7 tbi. It has 227000 original miles on the engine and tranny. It was running very s**tty. I replaced basically every module but it didnt fix it. Once i unplugged the idle air control and it ran PERFECT!! Once i bought a new iac and plugged it in, it ran like s**t again. Why does it run better with the iac disconnected than with a totally new unit??? Need help ASAP guys!!! Thanks a bunch.

[90GMCZ71]

I have a 1991 k1500 5.7 tbi. It has 227000 original miles on the engine and tranny. It was running very s**tty. I replaced basically every module but it didnt fix it. Once i unplugged the idle air control and it ran PERFECT!! Once i bought a new iac and plugged it in, it ran like s**t again. Why does it run better with the iac disconnected than with a totally new unit???  Need help ASAP guys!!! Thanks a bunch.

 

<{POST_SNAPBACK}>

 

 

 

Make sure the IAC passage is clear. If it is partial clogged, it may not work right.

 

The other possibility is that there is a bad wire or connection.

 

//90GMCZ71

[SPARK CHASER]

Don't know if this will help, but you should remove your TBI unit and clean out all the passages with a scraper and carb cleaner. On my truck I found the PCV port almost completely plugged with hard carbon. The IAC port had some carbon too, but not as bad. I also noticed the base gasket had deteriorated and might have been allowing crossover leakage between passages.