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Hi all, my girlfriend has a 2000 Grand Prix non SC 3800 with 155651 miles on it, when cold idles smooth unless you rev to 4000 rpm starts cutting out then as soon as it has run a few minutes the rpm starts bouncing around and it dies then wont start again till it has cooled for several hours. It had codes p0102, p0300 and p0420. Checked fuel pressure was 43 book stated should be 48-55 so replaced fuel pump. No change. Replaced coil packs and plug wires, plugs are fairly new. No change. Replaced ICM. No change. Replaced MAF. Cleared codes. No change. Checked vacuum lines, appear to be fine. No longer getting any codes but it wont stay running very long. I dont have much experience with these as I am old school shade tree mechanic. Any help would be much appreciated.
 

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so you replaced the MAFF sensor correct? did you also replaced the B1S1 O2 sensor? 43psi is about average, has the fuel filter been also replaced yet considering the motor has 155K+ miles? check the OBD-2 port again and see if ther are any other codes as well as any that are pending. lastly what are the plugs gapped at? and what cylinder(s) are misfiring?
 

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Yes replaced MAF sensor, relaced B1S1 O2 sensor awhile back dont remember exactly when. Replaced fuel filter about a year ago and again yesterday when I replaced fuel pump. There are no pending codes. Plugs were changed a few months ago i believe the gap was .45 and misfires are multiple random. This car hasnt ran right for a long time and only became undriveable recently.
 

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THe Crank Position Sensor may be failing when the motor gets warm. However, the rough idling may be due other factors..good luck KEV
 

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did u check and replaced the fuel pressure regulator? also try this method:


lastly, does the exhaust smell sweet or if the plugs when u pulled them wet with coolant?
 

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Ok I disconnected the MAF and the car will stay running. Did I get a bad one? Possibly. But still have the stumbling under load @ around 4000rpm. Leaving the MAF disconnected will result in what, poor fuel economy?
 

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noooo... never unplug the MAF sensor... Your fueling system is based on several sensors. The Mass Airflow Sensor is the base of the whole thing. Once you disconnect the MAF the car goes into a PANIC mode and creates emergency tables of fuel delivery since your sensor is disconnected. Bottom line is, your MAF sensor is probably working properly is just that your car wont run good with the amount of air and fuel supplied at normal conditions. Check two things; it sounds like you have an electrical problem. You might have an ignition module issue. I would take it to the closest Advance Store and have them check it three times (to get it hot and try to duplicate the problem). Also replace your spark plug wires if you haven't and lastly if none of the above works you must do two main things.

1) Check for fuel pressure (You can buy a fuel pressure tester at Advance Auto Parts) if good pressure.....

2) Do a compression test on all the cylinders (You can also buy the compression tester at Advance Auto Parts)

Let us know how it goes!
 

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Not true, Andres. Once you unplug the MAF, the engine runs on the open loop table, not a panic mode. Unplugging the MAF is a common troubleshooting procedure, and is 100% effective in determining a bad MAF.
 

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Yes replaced MAF sensor, relaced B1S1 O2 sensor awhile back dont remember exactly when. Replaced fuel filter about a year ago and again yesterday when I replaced fuel pump. There are no pending codes. Plugs were changed a few months ago i believe the gap was .45 and misfires are multiple random. This car hasnt ran right for a long time and only became undriveable recently.
After you run it for a while, take a close look inside the fuel pressure regulator tube to be sure it's not leaking fuel causing a rich fuel condition causing poor running. Jake
 
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