2000 GTP dies at idle

[jatchis]

I have a 2000 GTP with 140k miles. I drove it home from work Thursday night, pulled into the garage and shut it down. When I went to start it Friday morning, the motor spun over, fired a bit, but would not start. I pushed the gas pedal down a bit, and it fired right up, but it dies as soon as I try to let it idle.

Now, I can keep just a little pressure on the pedal, keep the rpms up around 900, and it idles fine, no noise, nice smooth acceleration, but as soon as I let my foot off the pedal, it stumbles and dies.

I'm asking here first because A- you folks know these cars, and have seen all this before, and B- the car was running great until I shut it off, with no indication of any problems, then the next time I apply power it won't idle. Seems like an electronic/sensor problem to me, and I would just like a little guidance on where to start first.

I have a pocket scanner, and the only code is a single (pending) MAF sensor code, but that only showed up when I disconnected the sensor cable and tried to start it (no change in symptom), so I caused that one. I let it run about 10 minutes with my foot lightly on the gas hoping a sensor might post a code, but no luck. The only odd thing I did notice was that when I let it die (and left the key in the on position), the fuel pump would run about 5 seconds after the motor died.

Could this be a fuel pump getting weak, especially at idle? Does the computer control the pump, altering voltages per TPS position?

Thoughts? Any advice where to start would be greatly appreciated.

John

[GTP Dad]

There are several possible issues here. First, rent a fuel pressure gauge and check the fuel pressure while it is running. If the pressure is less than 45 PSI you may be developing a fuel pump issue. The easiest thing to do is to change the fuel filter as it may be blocking up if you haven't had it changed recently. I would do this before checking the fuel pressure. If the filter change doesn't change things then you should check the pressure at the fuel rail.

The fuel pump normally runs on low except when the supercharger is providing boost then it kicks into high. I don't remember when GM got rid of the fuel pump resistor for the GTP but if this car has one it may be going bad and causing this issue. Sorry, I don't remember if this model has one or not.

The other thing would be to remove and clean the idle air control motor. Spray it with throttle body cleaner just don't move the pintle when you do. This is easy to do and doesn't cost a lot.

[jatchis]

You nailed it, GTP Dad!

I decided to do the easy one first, pulled the IAC out, and it was filthy. Sprayed it down, put it back in, and she idles like a new one again! The stupid lower screw broke off instead of backing out, but it will make it over to the shop with the one screw so I can drill the center out and get an extractor in there (or tap if I need to).

Thanks for the quick response and the great, accurate info!

[rickisrad]

clean out the throttle body very well also. The carbon build up does not allow the proper amount of air to flow through causing it to stall. I do mine several times a year as well as cleaning off the maf.