1996 Pontiac Sunfire 1996 Sunfire idling poorly

Engine Performance problem
1996 Pontiac Sunfire 4 cyl Two Wheel Drive 107000 miles

I would like to determine the root cause of a rough idle in my 1996 Sunfire. It idles fine when it is cold, but when the car warms up, it bucks like a mini bronco. (A big bronco would through me out to the car.) The bucking slows down and the speeds up. After a few seconds it seems to idle all right, and then goes back to idling rough. The car runs ok when driving, and the engine speed is above 1500 RPMs. I added fuel injection cleaner in the gas, and it helped, ever so slightly.

The ODB-II code displayed on the tester is P0171. The manual tells me that bank 1 (?) Is running lean. Is it the MAP Sensor? How do test the MAP sensor? Can something be loose?

Car has a 2.2L engine.
Do you
have the same problem?
Friday, January 22nd, 2010 AT 9:03 AM

1 Reply

Hi ray_in_GA, Welcome to 2carpros and TY for the donation

Try cleaning out the idle air control valve and EGR valve.

P0171-running lean could be one of the following:

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (Use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (Try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)
Was this
Friday, January 22nd, 2010 AT 4:01 PM

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