I have a 1986 Chevrolet Camaro 2.8L v6, I just found out that my exhaust manifold was cracked (saw black smoke coming up under the hood while adjusting TPS, and went to investigate and saw that I have a major crack in the exhaust manifold), my question is, what kind of problems can this cause? I just replaced a fuel injector because it was bad and causing problems with the car and now it runs 30x better but its idling awful and shuts off while im sitting still alot.

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1989 Camaro RS Convertable
350 ci Throttle Body Injection
(no mods yet, mostly stock except the 305 was removed and replaced with a 350)
Suggestions very much welcome!
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1996 Pontiac Firebird 3.8L v6 (Stock), Black
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1986 Chevrolet Camaro v6 2.8L (Stock)