1996 Pontiac Grand Prix dies at idle/stop

Asked by Pancho529 Dec 31, 2019 at 09:59 AM about the 1996 Pontiac Grand Prix 2 Dr SE Coupe

Question type: Maintenance & Repair

Good morning,

I have a 1996 Pontiac Grand Prix (3.1 v6) that dies at idle or low RPM (such
as coming to a stop, reversing, stop signs/stop lights, etc). It will try and
correct itself jumping between 500 and 1000 RPM before it loses power. It
will turn back on immediately. It runs at highway speeds just fine and I don't
notice any issues accelerating. It also seems to be worse in the summer time
when it's warmer. The service engine soon light comes on and I pulled a
code (P0131 oxygen sensor circuit low voltage bank 1 sensor 1). I feel like
it's not getting as good of mileage as it should be and I feel like the exhaust
smells more than it should.

I've done some research and it seems that it could be a bad oxygen sensor,
wiring harness, dirty throttle body, dirty mass airflow sensor, bad mass
airflow sensor, idle air control valve, or crankshaft position sensor among
other things. My father-in-law is set on it being the O2 sensor, but I don't
want to just throw money at parts, but it's also going to cost me $120 to have
it diagnosed. Any thoughts? I know it wouldn't be a bad idea to replace many
of the parts as this car has 300k miles on it and an engine that has 150k
miles. My father-in-law said he has never replaced the O2 sensor.

Side note... I found a random cord unplugged that sits behind the spark
plugs and have no clue where it connects. I'm not sure if this is part of the
issue or not. Here is a picture of it.

Thanks!
Tim

1 Answer

18,185

I think the loose wire is just a connection for a code scanner. Not likely the problem. I agree with you, find the problem before throwing parts at it. That rarely works. I don't believe a failed O2 sensor will ever make your engine stop or run poorly. The whole list of possibilities you list are indeed possibilities. Those things all need to be looked at first because any of them could make the computer "think" the O2 sensor is bad when its not. If neither you or your father-in-law are up to the task of sorting those things out then its time to spend the $120 and have it diagnosed. That money will help prevent spending other money needlessly. As for replacing the O2 sensor, it requires a special socket which your father-in-law may or may not have. If its the upstream one, which it probably is, (there are 2 of them, make sure you know which one is the problem) its much easier to get at if you disconnect the top motor mount and roll the engine forward to create room. Do some you tubing to find out how. Good luck.

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