High idle - no vacuum leak

[cbaclawski]

I posted this over on corvetteforums as well, I apologize if that is not ok:

Hello,

Everyone here was so helpful last time I thought i'd try again.

1990 zr1 lingenfelter 368

I am having an issue with my idle, and it's difficult to start.

My car idles ~ 1000-1100 rpm, and when driving, say approaching/at a stop, rpm's only fall to ~2000, before eventually(usually) settling back down to the 1100 area.

Also, it doesn't start immediately upon turning the key, it has to crank for a considerable amount of time before it "catches" and fires up.

I took it to a local repair shop, and they did a smoke test and said there were no vacuum leaks. The "GM Tech" there said it was probably the coolant temp sensor, but he couldn't be sure and didn't want to experiment on my car having never worked on a zr1 before.

After reading that it could be a dirty throttle body, I did my best to clean it this morning(without removing it - just removed the intake hose, sprayed cleaner in there with the valves opened and wiped) and it did not help(if anything, it made it worse - on a test drive this morning it "stuck" ~ 3000 a few times)

For an unrelated issue, I recently replaced the injectors, plugs, and coils. The idle issue is pretty much the same as it was prior to those changes, but the "hard to start" issue started after those items.

To address this issue I replaced The idle air control valve and throttle position sensor(I did check voltages). Neither seemed to do anything.

What would you do next? (I have the new coolant temp sensor, but am reluctant to pull the plenum again to change it without a second opinion)

Thanks in advance,

Curt