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Dr.Carz
Dr.Carz, ASE Certified Technician
Category: Pontiac
Satisfied Customers: 303
Experience:  12 years of exp. 10 with ford on my third with all other makes.Just love cars
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1999 Pontiac Grand AM 2.4 LITER missing bad at idle no codes

Customer Question

`1999 Pontiac Grand AM 2.4 LITER missing bad at idle no codes have replaced plugs, plug boots, coil tower, coils. runs good until you come to a stop misses so bad it will almost die.
Submitted: 1 year ago.
Category: Pontiac
Expert:  Dr.Carz replied 1 year ago.

Sounds like low compression issue poor valve seating a compression test will be needed should see 150 psi 3 hits.Double check plug gap while removing for compression test.good luck and keep me posted.

Customer: replied 1 year ago.

Have tested comp 150 to 160 all 4 holes, regapped plugs installed new cap a plug boots no change. I did notice short term fuel trim was at -32 and long term at -22, o2 sensors are staying in the 450 range. Could this be a 02 sensor problem?

Expert:  Dr.Carz replied 1 year ago.

Yes without a doubt these numbers help a lot. means the pcm is seeing rich check the vacuum line to map sensor if soft and spongy replace. Its near the throttle body I do recall this having a small feed line that gets soft spongy and sucks itself closed. Can you see MAP sensor reading volts/in.hg? You should be able to see a response from the o2 say rev it up and let off if it goes up .8ish and falls .2ish then it can see and have swing so leave it be if not the yes the o2 be cause but would more like to see stuck at .8ish for a trim of -52 combined more like in correct map or baro input.

Expert:  Dr.Carz replied 1 year ago.

Any luck curious to know how you have made out.

Expert:  Dr.Carz replied 1 year ago.

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