Idle to high around 2000rpms

[We Gone]

So I need some advice from the experts. I have a good friend here in Ga. who has a 91 P&P headers exhaust and tune If i had to guess 500 flywheel HP.

He can not get the idle down below 2000, This just started after the car sat for an extended time. I went over and helped check out the normal things such as vacuum or vacuum leaks none found. I hooked up my scanner and what I did find was a code 62, and the 02's never cross counted the stayed around 750-800 both right and left just a flat line??

He does run a % of race gas in it could that have burned up the 02's?
Will the 02's create this high idle issue?


Thanks Guys any help will be great.

[RussMcB]

Steve, are you sure there isn't a vacuum leak under he plenum?

When my (stock) ZR-1 had a 2,000 rpm idle, Marc H said (almost immediately) it was a vacuum leak, and he was right.

I'm not sure if fouled O2 sensors might cause high idle.

Good luck.

[Funracer]

I agree vacume leak. Last time I left a vacume hose off under the plenum
it idled at 2000. Pulled plenum again, reattached loose tube, prob solved.

[XfireZ51]

Originally Posted by We Gone

So I need some advice from the experts. I have a good friend here in Ga. who has a 91 P&P headers exhaust and tune If i had to guess 500 flywheel HP.

He can not get the idle down below 2000, This just started after the car sat for an extended time. I went over and helped check out the normal things such as vacuum or vacuum leaks none found. I hooked up my scanner and what I did find was a code 62, and the 02's never cross counted the stayed around 750-800 both right and left just a flat line??

He does run a % of race gas in it could that have burned up the 02's?
Will the 02's create this high idle issue?


Thanks Guys any help will be great.

IIRC a Code 62 is a left side O2 sensor running lean. Race gas could poison the O2. 750-800mv means rich. Could be ECM is trying to compensate. What are your IAC counts. I'll guess they're above 35.

[We Gone]

Originally Posted by XfireZ51

IIRC a Code 62 is a left side O2 sensor running lean. Race gas could poison the O2. 750-800mv means rich. Could be ECM is trying to compensate. What are your IAC counts. I'll guess they're above 35.

Thanks guys, The secondary vac system was in good shape and only cycled every 30+ sec. and than only a few burps. We did not want to pull the plenum just yet, may be my fault I got focused on the 02 readings. I to was thinking the ECM was trying to compensate, I don't remember the IAC counts and forgot to push the capture button.

We got to talking about car and stuff I had not seen Mark in many years so we had a lot to catch up on. I'll make a trip back when I get more information may be a few weeks as its about a 100 drive one way. Was a great drive in the 93 for me!!! but the cam cover washer I replaced was still seeping just a bit.

I hope he does not mind but this is his beast...One great looking ZR-1

[RussMcB]

I agree. Very nice.

[We Gone]

Any other ideas or comments.

[GOLDCYLON]

Originally Posted by We Gone

Any other ideas or comments.

You have verified the MAP hose? Its sounds like an under hose plenium leak. The MAP would/should show an open fault as well

[A26B]

Option other than bad O2: Verify whether the 2000 rpm idle is vacuum leak or throttle related. Put a heavy book or piece of plywood over the air horn while running. Engine dies, it's throttle or IAC related, keeps running, it's vacuum.

[GOLDCYLON]

Originally Posted by A26B

Option other than bad O2: Verify whether the 2000 rpm idle is vacuum leak or throttle related. Put a heavy book or piece of plywood over the air horn while running. Engine dies, it's throttle or IAC related, keeps running, it's vacuum.

Yep thats right Jerry anything that can block the intake I used a piece of cardboard it does the trick as well