misfire at idle

1997 PONTIAC GRAND PRIX
550 MILES • 6 CYL • FWD • AUTOMATIC
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GPGT97
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enter your question...1997 Grand Prix GT has multi. cyl.misfire and Bank 1 too lean.car has 500 miles on rebuilt engine,and runs great over 1500 RPM.Replaced MAF,cleaned and checked injectors,FP is 48 PSI with new plugs,wires and coils.Any vac. leaks have been sealed.This 3.8 NA has a comp cam with .531 gross lift,which makes the idle even more erratic.Engine had same symptoms before rebuild.The exhaust is extremely rich at idle.I have two Snap-On Scanners and the only codes they show are PO300 and PO171.
Could the O2 sensor be causing this?
Crank and cam position sensors were replaced about two years ago.
Jan 23, 2011 at 6:16 PM
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MERLIN2021
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02 Sensor will cause it as will vacuum leaks, 02 will take over fuel management when it's warmed up, cold operation the MAF does the enrichment. Check also the ECT(engine coolant temp) sensor.
Jan 23, 2011 at 6:29 PM
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GPGT97
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Thank for your advise and a remarkably fast answer.
I was going to purchase an O2,but smelled raw gas from the lower I.M.
Cylinders 1,3,5 had fuel bubbling under each injector on the intake.
I,m assuming the fuel rail must be cracked over the injectors because the o-rings and bodies were dry.It did throw a P1200 code before a 52 mile trip.all dry.ran great on I-20.idles bad.
Jan 24, 2011 at 5:08 AM
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MERLIN2021
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No more leaks on the fuel rail? Check fuel pressure with a gauge, and check the fuel pressure regulator, click on this link for a video on how it's done.
https://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm
Go here and checkout our video.
Jan 24, 2011 at 6:41 PM
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