Rep Power: 733

I think my IAC valve is receiving a signal that is keeping it wide open after the engine starts up. When the engine first starts up, it's ok. However after a few seconds there is a loud hissing sound coming out from the throttle body. It's causing a massive vacuum leak. This is a brand new IAC which I just installed last night. The IAC valve that I replaced was doing the same thing. The engine performance is real bad. I can hardly rev the engine at all, and it can hardly idle. I know the IAC receives a signal from the PCM, but what would cause the computer to keep the IAC wide open or fully retracted, if that is actually what's happening? I also just purchased the PCM (it is used) which was re-calibrated for my application. This condition existed with the previous PCM as well. Thank you for your support, Tommy.

 
Rep Power: 783

My money is on a MAF sensor.

 
Rep Power: 804

my money is on the vacuum hose going into the TB.. mine comes loose about once every two weeks and just have to stick it back on.. i need to put a worm clamp on it but i havent yet.. sounds like the same symptoms.. if you are looking at the tb from the front of the engine it is on the left side... and just plugs right into the tb.. it took me a while to even notice that it wasnt attached so check it lol.. its easy to overlook

 
Rep Power: 785

get a new one...slp, better performance and may fix your problem

 
Rep Power: 804

a new what? he cant get a new MAF.. or a new TB.. its a v6.. :banghead:

 
Rep Power: 738

Nobody makes an aftermarket MAF for the v6. Sigh...

 
Rep Power: 734

I second that. The 1st time mine came off, I sh*t a brick trying to figure out what was wrong with my car. It happened about once a month after that, but when it happened again, I already knew what was wrong. I put a zip tie on mine as tight as I could get it, and I never had anymore problems out of it. But it sounds exactly like what is going on with yours.

 
Rep Power: 875

if it is the IAC and the IAC is what im thinking of you can try cleaning it out...(idle air control right?)

 
Rep Power: 733

I forgot to mention that I'm working on an engine drivetrain conversion and that I had a special engine harness fabricated for my application. I just rechecked every wire connector, all vacuum hoses and everything else you can think of. In doing so, I found that the wire plug connector to the IAC valve is not the correct plug connector. It has the right wires and color, however, all 4 wires are not situated in the right position on the connector. Because of this, the IAC valve is retracting wide open causing a massive vacuum leak. The plug wire connector is probably from some other GM vehicle, perhaps from a different year vehicle. I'll let you know how things turn out when I make the necessary corrections. Thank you for your support, Tommy.

 
Rep Power: 733

I cut off the existing IAC wire connector plug pigtail, and soldered in the correct one. This resolved the problem. Thanks for your support, Tommy.

 
Rep Power: 875

yay!