I have a 93 pontiac sunbird, it starts good but runs very rough and backfires until it warms up,it recently had a new cylinder head installed, could it be a vacuum leak or timing problem or a carburater choke that is causing the problem?
by 
donsan
ANSWERS: 3
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Could be a clogged catalytic converter, the exhaust needs to be able to breath or it will choke on itself.
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your ambient or engine temp. sender is bad. when cold the mixture is enriched by a signal from this. cold engines will backfire or stumble on lean mixture.
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Why aren't the answers given helpfull? Either one is probably correct and by the way you don't have a carb. or a choke. you have fuel inj. with a cold start enrichment controlled by computer.
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