I have a 1999 Grand Prix GT, 3.8 L non-supercharged, that will run like new for days or weeks and then will for no apparent reason be very hard to start and will immediately die. If it does stay running for a minute or two, it runs very rough (like it's running on 4 or 5 cylinders) and blows black smoke. If you wait a while, (10 minutes to an hour), it starts and runs great like nothing was wrong! Plenty of power, pickup and good gas mileage. No check engine light, no computer codes. Has a new fuel pump, filter and fuel pressure regulator and still has the same problem. It seems to be getting worse in the last month. (more frequent and lasts longer before it will start and run right).
I have had two of these problems both on grand prix's , both turned out to be a mass air flow meter. but nethier set a code for the sensor.
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Pull the spark plugs right after it does this. See if any 1 is black. If so the it is something tied to that Cyl like a coil issue (common on the 3.8L aftre 100k). If they all look the same then look for a more general issue like a idle air valve, dirty MAF sensor, etc...
How many miles? If over 100k clean the MAF sensor. And you don;t have a K&N filter do you?
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