My 95 Z28 has been having a high idle problem. The thing has been idling at like 1,500rpm. I was told by Z28pete a while back that it could be the IAC motor or some other things like a vacuum leak. I took the throttle body off and cleaned it REALLY well.(it was ugly!). According to my Chilton's manual, you can check the IAC motor with an ohm meter by connecting 2 of the 4 connectors at a time(first the left two, then the right two). It says if the ohm resistance is between 40-80 ohms that it is good. Mine checked out at 52-53 ohms. I asked some techs at the local chevy dealer about this and they said you can't check it like that. They said to hook the IAC back up to the wiring harness and turn the car on and check to see if the valve opens and closes. I don't know if they meant to actually crank it or just to turn it to the accessory on position. I just got off the phone with a guy at the dealership who said you can't check it that way either. He said you'd have to get jumper wires and connect the IAC motor straight up to a 12V battery and see........ What do you guys think? Everything should be getting power with the ignition switch turned on right? I tried that and the IAC didn't do anything. One guy said the thing had to be grounded. I tried doing it again with the IAC's mounting face touching several good ground points and that didn't work either. I'm gonna go ahead and put it back together. The air intake boot was split at 3 places where it connected to the throttle body. I had it taped up real good but I went ahead and bought a new one as well as a new throttle body gasket. I also cleaned the IAC motor real good, just incase maybe the carbon was gunking it up where it couldn't work right. If anyone knows more about this or has an idea of what else might be the problem, let me know. Until then, I'm gonna see if what I've done already might have fixed it. Thanks for any help anyone can give.

Josh

 

I'm still wandering how to check this IAC valve/motor. I reinstalled everything and the problem is worse. When Itried to start it up, it tooka few more cranks than normal to start and immediatelywas idleing at 1500rpm. I let it run for a minute and it slowly crept up to 2000rpm, then it started having these spells where it wouldchug down to 1000rpm or so acting like it was gonna stall out and then go back up to 2000rpm. The check engine light is not coming on. I tried spraying throttle body cleaner around the intake manifold and all the vacuumhoses I could reach to see if that would reveal some kind ofvacuum leak and didn't notice anything. I just installed a brand new air intake elbow, no other obvious air intake leaks. I am gonna jack it up and try to check all the vacuum lines that go under the car and I'm also gonna check all the secondary air to/from hoses. I was told the best way to find a vacuum leak is to spray carburator cleaner around the air intake manifold and vacuum lines. I was told that this would make the engine rev upa bit and thus you could tell where the leak was. Will throttle body cleaner do the same thing or does itneed to be carburator cleaner? I really need some help on this so any advice would be appreciated.

Thanks, Josh

 

I just replaced the IAC. That didn't fix anything. Anyone know how to check the TPS? Also, what is the absolute best way to finda vacuum leak?

 

hey why do you try to change the pcv valve, it could be bad and it could cause rpm problems as well. try to change it its cheap 4-6 bux, try not to break the hose, or be ready for it to break they age and harn over the years, if it breaks try getting it from the dealership near you.

 

The PCV is built into the left valve cover. I'd have to buy a new set of valve covers to replace it I'm pretty sure. I actually broke that hose last time I had the valve covers off, LOL! (decided it would be a good idea to paint them orange) I bought a new one from the dealer already.

 

When you get this figured out let me know... If I figure it out I will let you know cause I have the same exact problem.

 

Ok... I pulled my IAC valve back off the car today and checked itAGAIN with a voltmeter. I got 53 on the top 2 and 8 on the bottom 2. I took it back to autozone and they gave me another part. I put it on and it fixed my problem. You may want to recheck yours. I checked it according to the Haynes manual and also according to every other website on the net. So you can pull it off the car and check it. You're only checking resistence values anyway. It doesn't need tobe plugged to the car for that. Oh... also, I was looking at a corvette forum site last nightat thevette's with the same engine as mine and another fellow was having the same issue. He suggested changing out the TPS. Well I did that too since it wasn't but $30.00. So it could have been a combination of both.