1996 LT4, rebuilt engine a little over a year ago. This included a new IAC injectors but I am still on the original MAF.

Saturday I needed to move the car from the driveway to the street. At start up it idled at 1500. Normally it sits about 900. Few revs and it didn't change. I decided to drive it around and see if it would change. Took it around until it was fully warmed at 195 degrees. Each time I pushed in the clutch it would idle at 1500.Switch on and off the AC and no change. Usually if I run the AC it will idle a little higher than normal, maybe an extra 100.

I am thinking vacuum leak. Oh what fun lies ahead... The sun was out and blazing, since I don't have a garage to work in so I just parked in on the street. I came back that evening to move it back for the night and it idles perfectly like normal. What? Drive it around, wake up some neighbors you know the usual stuff, and the idle worked just fine.

The car for the past year has been totally predicable and very reliable, actually I have been very impressed with the car and how well it works. My neighbors hate it, its loud. I did rebuild everything you can think of but the electrical is all original and uncut with only a couple of items changed during the rebuild/restore.

After the rebuild I had to mess with the idle only to find a bad IAC and a BAD IAC replacement part causing my issues. Not a vacuum leak as I first suspected. With the proper IAC from Standard Electric and a small manual adjustment I was able to get it right using the scanner. The 96 on ODBII makes it a little different than the others.

Any ideas on the idle weirdness?

 

No codes thrown at all?

 

Don't worry about it until it starts happening on a regular basis, life is too short.

 

If you have a scanner monitor TPS value and IAC counts. If idle is high and IAC counts are 0.there is vacuum leak.if TPS value is high at idle IAC will retract increasing idle speed.

 

Worn throttle blade shaft bushings. Blades are getting hung up on the throttle body housing before they close completely. Next time it happens, try blipping the throttle (like kicking off the choke on a carb). Or check under the hood to see if tbe throttle is fully closed.

 

I will scan it and see if there are codes. I blipped the throttle a few times and nothing changed. I drive it yesterday and it acted ok. Now I am really paying attention to it. Will let you know what I find.