Very rough idle after hot start

[kenwa]

My 96 LT1 runs fine except after a hot start. It starts immediately when the engine is cold, but after running for a while (20-30 minutes) and getting thoroughly warmed up, then sitting for about 30 minutes, it is slow to start and barely will idle. Can't even run the AC or it will die. Sometimes dies anyway. Stepping on the gas, it is very slow to rev up. If I get it reved up (3000+ RPM) and hold it, it will stay going okay. After a minute or two of this, it smooths out and runs fine again. There are no codes or check engine light at all. Like I said, it runs great the rest of the time. Any ideas? Thanks.

 

[boomdriver]

My 96 LT1 runs fine except after a hot start. It starts immediately when the engine is cold, but after running for a while (20-30 minutes) and getting thoroughly warmed up, then sitting for about 30 minutes, it is slow to start and barely will idle. Can't even run the AC or it will die. Sometimes dies anyway. Stepping on the gas, it is very slow to rev up. If I get it reved up (3000+ RPM) and hold it, it will stay going okay. After a minute or two of this, it smooths out and runs fine again. There are no codes or check engine light at all. Like I said, it runs great the rest of the time. Any ideas? Thanks.

I'd start with the basic checks...

fuel pressure first, look for a stable reading with no fluttering of the needle or quick, erratic movements. The only movement of the needle should come as the rpm is increased then it should quickly and smoothly return to almost where it originated. After that, then I'd look at the temp sensors (cause a LOT of grief) and finally I'd look into clogged cats.
Most often an engine won't rev because there is not enough fuel to go with the amount of air available, OR because it cannot exhaust what has already been burned.

The levels of back pressure are pretty low...by pulling an o2 sensor and installing a pressure gauge, at fast idle the pressure in the exhaust should be no more than a couple lbs... any more than that indicates a clogged Cat.

Thats also a good arguement against hacking up an exhaust system thinking that cats and mufflers are TOO restrictive in the stock system. If 2-3lbs is the maximum for a good system with an 8 cyl engine this size, thats just not much in the way of restriction. It takes a clogged cat to create pressures greater than 2 lbs....