My car has always idled around 900 and will drop to 700 when in gear. It is a '92 LT1. I have 17lbs of vacuum. I can pull a hose off to make a vacuum leak, and it will raise up more. I have sprayed carb cleaner around the hoses and nothing. Also I have put on a different TB (with IAC) and MAP sensor from the intake I bought for my new engine. Everything was the same.

I'm not too worried about this issue since I am working on another engine. Plus there is a vibration in this engine almost like a bent pushrod, valve or rod. It will smooth out at high rpm's, but felt mainly around 1-2k. Maybe this is part of the problem.

Have you unhooked the IAC with the engine running? If so, it needs reset.

Quote:

No, but I will reset it to be sure.

How much higher is the idle? Have you inspected the tb blades to see if closed? Did this start after you adjusted the ASR?

Matthew

Quote:

It is around 900. I had a spare TB that I had cleaned up, so I put it on last fall. It still acts the same way, and has always idled there. With the ASR adjusted now it shifts way too soon.

The PCV felt like it was a bit sticky, so I am going to clean it. I need to get a new section of hose. This one is brittle and had sealant over a crack from where it was removed earlier.

Quote:

My 92 idles somewhere around that. I've been wanting to check it out but haven't got to it.

Plus mine sticks a bit at 1,200 coming up to a stop then drops to idle abruptly.

Bill -

Do the lt1s have an idle adjust procedure like the l98s? Is there a throttle blade adjustment?

Tj - if you remove the throttle cable from the tb does it still idle high? Can u take the duct off and verify the blades are closed?

There is a stop for the blades on the tb. I cleaned the blades before this one when on to be sure they would seal all of the way around. The throttle cable allows the blades to be fully shut.

Bill, what did yours used to idle at?

Quote:

Ya know, I don't remember. I think this started after I cleaned the TB, had the IAC off, etc.

Playing with it is on my list of things to do but it's not very high on the list and doesn't affect driving the car.

I cleaned the PCV and put a new hose on it. It idles smoother, but still at 900. I also double checked the blades to be sure they were fully closed and that the throttle cable was allowing them to the stop. I also sprayed another round of carb cleaner at various spots.

With the stock throttle body, there is no idle adjustment that is EASILY available, as the ECM is supposed to control idle RPMs via the IAC. There is a set screw that the throttle linkage comes to rest against on the driver's side of the TB, but the adjustment screw for that is sealed at the back of the TB. You would need to drill out that seal in order to access the screw. Since your idle is high with two different throttle bodies, I would be suspect of the IAC passage, or the IAC valve itself.

You can unscrew the IAC from its port and spray a bunch of carb cleaner in there, but really the best way to clean the passageway out, especially on a car that has been in service for 20 years, is to remove the TB, remove the IAC/coolant manifold on the bottom of the TB, and scrub the insides of the manifold completely clean with TB cleaner and an old toothbrush. Put it all back together with new gaskets. Also (speaking from experience here), do NOT fiddle with the IAC pintle when you have the IAC removed. Wipe the tip off, sure, but don't try pushing or pulling on the pintle.

I may not be a complete Guru, but after spending the last year and a half banging my head against a wall trying to solve a high idle on my '92, I know the whole TB/IAC/idle control process pretty well now. My problem turned out to be a flaky ECM. She idles at 550 - 600 in gear now, and around 700 - 750 in Park or Neutral. SO much nicer to drive!