rocky1

A buddy of mine asked me to help him out with his 1987 Corvette. He says that this is a new problem that just showed up.

When I looked his car over, I noticed a high idle even when warm (1100rpm). When driving it, it is low on power and you feel it missing. There are no trouble codes.

I assumed that he had a vacuum leak. I put my vacuum gauge on it, and it read ~20"h.g. and steady. So, I don't think that there is a vacuum leak.

Figuring that the air to support the high idle had to be coming from somewhere, I thought Idle Air, or Throttle Stop screw. He says that he hasn't messed with the "idle screw" on the side of the throttle body. Based on that, I thought that I'd investigate the Idle Air Control.

I get the same idle speed with the Idle Air control connected or disconnected. With the A-B terminals grounded in the ALCL connector and the ignition on, but the engine not running, a test light lights when you ground one end and touch any of the four terminals on the Idle Air Control connector.

Just some additional background info: He says that the plugs are brand new. The TPS and MAF were replaced last year, and it ran fine till just recently. Fuel pressure was around 42, and increased when I disconnected the vacuum to the regulator. The oxygen sensor reading is low at idle. Seems to be hanging out at .3 volts. If I pull the PCV valve, it goes down to about .2 volts. If I increase the fuel pressure by disconnecting the vacuum to the fuel pressure regulator, it goes up to around .55 volts.

Is it likely the IAC? Any other tips?

Thanks

Mike

rick lambert

Mike, I think I'd double check the vac. lines for leaks. Although the IAC is usually suspect because it seems to be a carbon magnet, I haven't experienced it causing a miss or loss of power.BTW, you can't buy a IAC gasket..they don't sell them separately, and a new IAC with gasket is about $30.

RRT vette

with double checking all the 1000 vacuums on these cars. If you haven't cleaned the IAC, this is a maintenance item along with the TB. This might help from Vader86 webpage.

http://temp.corvetteforum.net/c4/vader86/tpsiac.html

onedef92

Clean the TB and IAC pintle (the spring gets clogged with carbon) and I'll bet that fixes the problem. It did on my '92.

Check the C4 TechTips section in this Forum for the TB and IAC cleaning procedure.

RRT vette

https://www.corvetteforum.com/techti...D=55&TopicID=2

rick lambert

If I remember correctly from a past post there is a step missing in
that tech tip, it's been pointed out you must disconnect the EST wire while doing this.

rocky1

Hey guys!

Thanks for the tips.

It was a combo problem: IAC & a cracked #2 plug. I'll be using the idle speed reset procedure that was kindly posted.

Regards,
Mike