This engine's in 87 chevy celebrity but I know they used these engines in f-bodys. I have cleaned the IAC motor and throttle body. As soon as you start the car it revs up really high. These are the things I have done.

I have backed off the idle screw all the way, doesn't make any difference.

unplug the IAC while the engine is running, it will stumble a little bit then rev up again.

disconnected the TPS sensor, stumbled, then idles back up.

After running last night for about 10 minutes, it slowed down to a rough idle.

Since I don't work at the shop I used to I don't have access to a scanner.

I thought maybe it was a vacuum leak, but I checked and can't find any and don't heay any.

I disconnected the MAF, made no difference, disconnected the MAP and the MAF, made no difference.

I am wondering if it's a bad computer, because I don't understand why it would rev so high, especially if the IAC is unhooked.

I have checked the cruise control and its not keeping the throttle open. I am getting close to running out of ideas. I am going back to work on it again here soon.

Thanks guys.

 

That is very odd that it would idel that high. The only other thing that I can think of are if you have air conditioning the solonoid could be sticking to make it rev high but I'm not sure it would make it rev at 3 grand. Mabey the spring that pushes the throttle back may have come loose. Is it carberated or fuel injected? If carbed maybe a sticky choke. Thats all I can think of at the moment. Hope it helps.

 

I plugged the air intake tube with a rag and the engine still ran, that tells me it's getting air from somewhere else. I'm going to pull the upper intake off and see if the upper plenum gasket has been sucked in.

I can't think of anything else that would let the engine run with it's only air source blocked off.

Jason

 

I took the upper plenum off and found two leaks on the same runner, i put some permatex on it and bolted it back together. it seemed to help some but it was still idling bad, surging and such. I took the plate on the top of the TB that has the passages to the IAC motor. That was open and not clogged up, but noticed the IAC hadn't moved, I turned the key on a few times trying to get it to move but it didnt. I tried turning the IAC but it just broke, if it wasn't broke before, i think it was, it defintely is now. I turned the IAC all the way out so it was closed and put it back together. Tried to start it, just as i thought, wouldn't start, it wasn't getting any air, if i held the throttle open it would start, so i turned the idle adjustment screw out some, the thing idles perfect. Now, is the IAC bad, the coolant temp sensor bad, or the ECM bad.

If i manually shut the throttle blades hard, the idle would come down, and if i backed the idle screw way down, after I came to a complete stop, it would idle down but be really rough. Thats when I checked the IAC motor, it seemed it was getting air.

As i said the car runs great now that the IAC valve is all the way closed and the throttle blade opened a little more. the engine doesn't miss like I think it would if it had a vacuum leak.

any thoughts?

Jason