Erratic Idle; HELP!
 

Here's the deal, I just bought a '95 Z w/ 74,000 miles. It starts fine, kicks into high-idle and then runs fine for about 30sec. At that point I can hear a high-pitched whine start somewhere in the engine bay and the idle starts to surge from 900-1400rpm. This continues until the whine stops, 1-5mins, and then it idles fine. Could the IAC be the culprit? I'm new to FI engines and don't know where to start troubleshooting.

Thanks
Dave

Just a thought, but it could be the A/C compressor or the alternator. Try to locate the noise. The compressor is on the alternator side, only attached to the bottom side of the engine, so you'll hear it from under the car nose.

The noise is NOT coming from any typical accessory... I cannot pinpoint it, but it sounds like an electric motor ( or a vaccum leak) I am pretty sure it is not a leak, because it does it EVERY time I start the car, and goes away EVERY time after 1-5 mins...

Dave

air pump then?

not the air pump...

As I said, i think it is something being activated... It starts about 30 secs. after I start the car. The noise comes on(whirring high pitched sound) and at the same time, the idle begins fluctuating from 800-1300 rpm, like some revving up the engine. This lasts for 3-8mins EVERY time I start the car. Then the high pitched noise stops, and the car idles rock steady.

I've taken a quick look for any obvious vacuum leaks, and checked for an intake gasket leak (propane test) but that's not it. Any ideas? Should I pop out the IAC and check it?


Thanks,
Dave

SOunds to me like the brake booster line.. It goes from a little box on the side of the manifold to the lower connection on the TB.. That would make a whine and cause your idle to bounce around... http://shbox.com/1/map.jpg .. Thats the only pic i could find close to it.. its the bottom black hose going to the TB.. LEt me know if thats what your problem was..

I'm pretty sure that hose leads to the cannister purge solenoid valve ,not the booster... anywho, I checked it out and it was pretty beat-up, so I rigged up a replacement. Car still has problem. :(

Can someone explain to me when (under what conditions) the AIR system operates? I only hear the noise when the car is first started. It doesn't matter if the engine is warm or cold.

Dave

Thats just what i call it.. When I did seafoam a LLOOOONNG time ago I read a diagram where it said to pour it in there and it called it the brake booster.... Eh... same thing, you got what i meant obviously..