When I start my car and drive it misses badly and losses power, but if I let it warm up for 10 minutes it doesnt miss. And, when I put it in park and press the accelorator it pulsates
Missing and loss of power on 2003 Buick Rendezvous
When you rev your engine in park the computor will limit the rpm to about 2,000, that is why you feel the pulsation. As far as the misfire - is the service engine soon light flashing? IF so, you should have the problem diagnosed ASAP. Damaged may have already been done to the catalytic converter. There a too many possibilites for an engine misfire to mention them all. If the service engine soon light has been on there should be a fault code stored in the engine computer which can help diagnose the cause of your misfire.
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I am having the exact same problem with my Rendezvous 2003. My mechanic told me that it is the transmission which has gone bad and has to be overhauled. He claims that these suv's are the worse SUV's he has seen so far. Too many things malfunction on them, one after the other. And Buick does nothing about it.