Stock 2000 Auto Z28 - Idle does not drop quickly anymore.

**emarkay** · 11-01-2007, 08:17 AM

Original owner, not abused, no mods but an air lid. 90K miles.
IAC (and passages), EGR, ASR linkages and Throttle plate and body cleaned with Gumout and vintage "tuner cleaner" (freon) (MAF and ASR with only "tuner cleaner").
The IAC had some carbon deposits but cleaned easily with cloth, everything else just dusted with carbon.
Everything is clean in and out, no vacuum or fuel leaks.
Throwing no codes, nothing stored in FF or Pending/Immature.
IAC motor cycles properly thru full range.
Base Idle set to about 600 via Torx screw.
Car has good vacuum indicated and no problems there.
Linkages smooth, return spring tight as installed.
Reset fuel trims and no change.
No other problems except idle:

More often than not, letting off gas at about 55, idle goes to about 2000, and stays for a while, then slowly goes to about 1200. Othre times just meanders down to about 800.
Car Idles OK, but a bit fast in gear (1000), and in high gear car wants to go about 35 MPH - hard to keep cruise at 30 MPH slow zones.

I am stumped. Service Manual mentions a air sealing compound applied to backside of throttle blade "to prevent air leaks at idle", but being there's already a bypass hole in the blade I don't understand what this does. But, could I have affected this sealing material by cleaning the throttle bore and plate? Should I try plugging or shrinking the hole in the throttle blade?

I will log the car tonite to see what the IAC counts are while driving, but I don't think that's the problem.

Any ideas? Could it be a PCV issue (but that would throw off vacuum readings, correct?)

Thanks.

MRK

**slims00ls1z28** · 11-03-2007, 05:35 AM

TPS working right? Did you remove the throttle body to clean it or just spray it on car? If so is the gasket sealed good? Or is there by chance any manifold leaks? Sounds like either some electrical gremlin or a small intake leak to me.

**emarkay** · 11-03-2007, 07:25 AM

TPS is giving good voltage.

Cleaned TB on car.

It's working closer to normal now - I really looked everything over real well, and recleaned the IAC passages in the TB, and "dry ragged" with a paper towel (a mild mild abrasive, btw) everything I could reach in the TB. I was going to relog wit hEFILive, but since it seemd better I didn't.

A few days on, now I can't remember how quickly it used to return to Idle (I know go look at your old logs) but SOTP it feels slower. But most important, the idle is now about 800 when "idling" so car no longer wants to idle at 35MPH in high gear.

Prob some strange artifact of global warming, laws of entropy and the ageing nut behind the wheel.

Thanks!
MRK

**0rion** · 11-03-2007, 08:39 AM

just something to check. Look at the hose that goes into the side of the intake from the pcv valve. Make sure there's not a rub hole on the back side of it or it isn't cracked. Definitely sounds like a too much air issue. I've saw where people have had that hose get a rub hole in the back side of it. Just something to look at.

**SeVeReDiStOrTiOn** · 11-03-2007, 08:28 PM

Originally Posted by 0rion

just something to check. Look at the hose that goes into the side of the intake from the pcv valve. Make sure there's not a rub hole on the back side of it or it isn't cracked. Definitely sounds like a too much air issue. I've saw where people have had that hose get a rub hole in the back side of it. Just something to look at.

Sounds like you're getting unmetered air in....also check all vacuum lines.