I have installed a 5.7 in my '72 chevelle. I put the first one in in 1999. it had l98 aluminum heads, tpis goodies and prom. the crank broke and scattered the botom. I then put in a stock 5.7. It runs rough at idle and at low speeds. it clears up and runs fin after the car is moving above 15 mph or so. my brother was checking it with his OTC scanner and it only runs rough in open loop. I have headers and the o2 is in the right collector. I have also have a hyper-tech prom. It did the same thing with the built engine. Anyone have any ideas?

Anybody have any ideas? There is no CEL coming on either. I know it is in an A body, but is a camaro engine and trans. LOL

Is the TPI system you installed a MAF or a MAP? If it's a MAF system, check for vacuum leaks anywhere between the engine side of the MAF sensor and the intake plenum. I had a leaky gasket between the back of the throttle body and the plenum on my MAF system, and it caused surging at idle. If you have a MAP system, check the vacuum line that goes to the MAP sensor. If you end up not finding any vacuum leaks anywhere, try cleaning the IAC solenoid and passages in the throttle body, and also check your TPS sensor voltage to make sure it's in spec.

Whtas the 02 sensor doing at idle? and are you in open loop? you may need a heated 02 if you don't have that.
And try to find the correct stock prom..

I'd start with the IAC. If its clean and working good, move on to the other suggestions.

I have a SD LT1 in a '71 Pontiac Ventura that I have that does the same thing. However it doesn't have a stock cam in it and it has a performance chip in it and it runs a tad rich in open loop. Once it warms up the symptoms go away. While its acting up, the IAC struggles to keep it running but it never stalls! lol

+1 Do you have a heated o2 sensor?

it is a MAF system. The throtthe body is a new unit from TPIS 52mm i believe. I have checked for vacuum leaks. replaced and adjusted the tps. I do have the heated O2 sensor. It only does this when it is in open loop, at idle or slow speeds, below 15mph or so under light throttle.when in town trying to maintain the speed limit. If accelerating, or wot it runs fine.