chrishall1984

My 91 idles very high in park in neutral then kinda goes lower in all the other gear ranges any body have any ideas. I was told it could be the MAP sensor but want other opinions before i go throwing parts at the thing. Thanks for the help.

InjectorsPlus

iTrader: (1)

Sounds like an IAC.

chrishall1984

I tried to take that out and clean it. And sometimes when I have the brakes on the back tires try to drive can the iac make the car think its driving or something or is that the map sensor

InjectorsPlus

iTrader: (1)

maybe it needed replacment, not cleaning. The role of the IAC is to maintain proper idle when you put the car in gear, or turn on the AC, basically anything that effects the idle of the car, the IAC keeps it consistent.

LeeH

iTrader: (2)

Have you checked the voltage on the TPS as well? 90's on up have a non-adjustable TPS, and it may be out of range now. Could also be a vacuum leak and a couple of other things...

InjectorsPlus

iTrader: (1)

Vacuum leak is the first thing to check, I'm getting sloppy....

The easiest way to do it is to find a local shop with a smoker. It takes no more than 10 minutes to smoke the engine, they should do it cheap enough.

chrishall1984

I changed the tps little under a year ago it shouldnt go out that quick would it

InjectorsPlus

iTrader: (1)

Nope, typically they last for years, was it a GM part? Sometimes the aftermarket ones stink.

I do think you need to look over for vacuum leaks first. I missed that step. Eliminate the cheap and easy first. Ascom's razor..

chrishall1984

i have already had it smoked about a month ago they did not find anything

chrishall1984

do u know which wires to back probe to test tps sensor

chrishall1984

Ok so I found out it is more than likely the IAC because I started the car disconnected the MAP and it died. I restarted the car and disconnected the IAC and there was no change in idle or anything. So I take it that means its not working anyways.

InjectorsPlus

iTrader: (1)

Since you had it smoked and did this, I'd be leaning IAC too, without having seen the car of course.

Question for you, when you replaced it last year was it an AC delco, or was it some aftermaket brand.

I've heard some aftermarket brands being unreliable, just would like to know for my own information.

chrishall1984

It was one I bought from autozone so dont really know if it is ac delco or off brand

chrishall1984

Just replaced my IAC and the high idle is gone now.

InjectorsPlus

iTrader: (1)

Thanks for the follow up. This validates my position that aftermarket IACs shouldn't be used. Yeah, they are cheap, but so what if you have to buy them twice.

Thanks again for posting the conclusion.

chrishall1984

Your welcome