'88 IROC, brand new ZZ4 crate with TPI, converted to 5 speed, all the right parts, freshly tuned.
On startup the car runs and idles just fine.
When driving, idle won't come all the way down between shifts or when coming to a stop in neutral.
It will usually hover between 1200 and 1500 rpm.
The idle will settle down nicely if I "blip" the throttle.
Is this problem easily cured, or is it indicative of a shot iac?
Thanks if you can help.

 

There are several possibilities. The ECM is programmed with a fuel cutoff on decel, and stall-saver programming (a kind of electronic dashpot) to prevent loading and stalling between shifts. You may be experiencing some of that programming, although it should not last for more than a second or two before RPM drops to normal target idle.

There may also be binding or misadjustment of the throttle cable/linkage.

There may also be wear in the throttle body causing throttle plate binding in the bores, preventig full closure of the throttles. The same situation can occur with a throttle body which has accumulated varnish and dirt from normal operation (what most people errantly call "carbon" in the TB).

Clean and inspect the TB and the IAC. Check for throttle shaft/bushing wear, and make sure the throttle linkage or cables are intact and not hanging.

 

ok, now i havent got quite the same set up as you but one of the things i do have is a borla adjustable exhust and when i put the plate with the smallest hole in it i got exactly the same thing your on about. as you havent said what exhust you have i just thoght it was worth a mention, you never know....!

 

i got a 92 trans am, with the tpi, and it does the same thing, i have not gotten around to fix it, but i was told it could be a vaccume leak. check the pcv valve on your valve covers, if you got a reserculatory valve, check that as well valve (forgot the same, it re-burns emitions), check that, then listen for leaks. and clean your throttle body with cleaner safe for O2 sensors