Hello all! I just purchased a 1990 C4. I got it from an estate sale super cheap due to a rough idle and stalling issue. It's been sitting about 1.5 years. It has fresh gas though. Engine was rebuilt 60km's ago. Mods included, 10.5 pistons, LT1 cam, hv oil pump, double roller chain, ported heads. Has no knocks or clicks, good compression, good head gaskets, good fuel pressure. Engine starts up well but runs rough, stumbles, seems to get worse when warming up. Like a vacuum leak but no hissing sounds. Possible EGR valve? What happens if I disconnect the vacuum line and plug it? Possible TPS or IAC issue? Anyone else have this issue who could help? It's a very nice car that had a lot of money put into it...just runs like a pail of s***!