what could be wrong with my 1989 Buick Regal?It will only go 15 mph . on 1990 Buick Regal

I have a 1989 Buick Regal 3.1,last year I changed the fuel pump and fuel pump screen , and it ran fine, now this year it started missing real bad, so I changed the plugs and plug wires and it ran fine for a bit then it started acting up so I put a new air filter in it and fuel injection cleaner in it and its still acting up only will go 15 mph and then dies , after about 15 min. I also had the catalytic converter checked and its fine and the fuel pump is working to, so please what could be wrong with it this time?

by in Sacramento, CA on December 02, 2012
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2 answers
ANSWER by , December 02, 2012
Have any trouble codes? Tap test MAF or get it tested.
ANSWER by , December 03, 2012
mass air flows are a common issue in this yr