Jeep dies at low RPMs

1996 4.0L HO.

is the best. This one has me scratching my head. Maybe you guys can help. My Jeep shakes around, sputters and dies at low RPMs, Not low speed or idle. It does better in Park, and if i keep pumping the gas, it'll catch and run, and does fine going up hill, but dies if I drop the RPMs going downhill. The whole thing is intermittent. It does it for an afternoon really bad and then is fine for a few weeks.

I've changed both O2 sensors, cleaned the air filter, and have gotten gas from several different places thinking it might be bad gas. Fuel Pump seems to work like normal, and there's pressure in the line up to the engine.

The check engine light was on and Autozone's reader said:
"P0171"

Definition
Fuel trim bank one condition
Explanation
The powertrain control module uses the oxygen sensor to calculate the air/fuel ratio of the engine. The computer has recognized a rich or lean condition on one engine bank only.
Probable cause
1. If bank one and two codes set together suspect fuel pressure or MAF (Mass Air Flow) sensor
2. Oxygen sensor defective
3. Ignition misfire - repair
4. Fuel injector problem.

Has anyone had this problem? Suggestions?

Thanks a ton,
Tom

1. Start with fuel pressure. MUST be tested with a gauge. For a 96, you should have 49 psi, plus or minus 5 psi

2. Test map sensor. Ensure vacuum leading to the map sensor is pulling "good" vacuum

3. Be sure tuneup hardware is fresh. Champion plugs gapped to .035, new wires, distributor cap, rotor

4. Ensure all vacuum and ccv hoses are intact and in place

Also check the tightness of you intake/exhaust bolts. Could loose vacuum if loose.

Thanks guys.

It seems to have fuel pressure enough to hit 80mph on the interstate, so I understand that's probably enough (though a gauge would show for sure.

I'll check the map sensor.

Just did new plugs gapped to .35, wires are pretty new, and can't remember on cap & rotor.

I'll check the vacuum lines.

Good idea on the intake/exhaust bolts. I haven't checked those but I wouldn't have thought of that.

I've also heard it could be the idle air control valve/motor, especially with it being related to when the pedal is engaged or not. I'll clean that out with the throttle body.

Thanks guys.

Be careful not to spray the TPS. I cleaned my TB out and hit it with cleaner and shorted the thing out.

Cool. Thanks!

First thing I would do is clean the idle air control valve. Remove the assembly from the TB and spray it out with carb cleaner. If it's really filthy may want to replace it.

Also clean the connectors for the air temp, air pressure, and coolant temp sensors. I had a rough low idle that was eventually tracked down to loose connection on the manifold air temperature, which made the computer interpret the value incorrectly, resulting in bad air-fuel ratio. The coolant temp sensor can prevent the computer from entering closed loop and will make the car run like crap