2002 ford f 150, engine lopes at an idle - Cars & Trucks

SOURCE: engine lopes while idling or idles erratically

vaccum hose back of intake manifold, check elbow rubber fitting for any cracks.

SOURCE: 1997 ford ranger idol problems

MIGHT be the tps
The TPS is sensitive to heat, moisture and vibration leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following: -

• Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".

• High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.

• Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.

• Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted acordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.

• Engine Misfire: A fault TPS can report values outside the deined acceptable range causing the ECU to incorrectly fuel the engine. This is noticable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessing misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.

1. With the engine off, insert the key and turn the ignition to position 2 (On) without starting the engine.
2. For MEMS-equipped cars (S1), quickly press and release the accelerator pedal several times (at least 5, but to be sure 8 or 9) using as much of the throttle travel as practicable. This will trigger the ECU into the closed-throttle reference learn algorithm, which has it looking for the lowest measured static throttle position (the closed position). The throttle position calibration is a fixed definition from this point.
3. Turn the ignition off, remove the key and wait for the ECU to power down (about 30-40s).
4. Start car as normal.

Marvin

• 85242 Answers
• Posted on Mar 15, 2009

SOURCE: engine idle

dirty intake throttle valve and air bypass idle speed control motor. ttry the following.

Here is the most common cause of surges and stalls at stops and low erratic idle speed and rough idle, it is the idle speed control air-bypass valve and throttle valve (IAC for short), they get full of gunk over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

SOURCE: 2001 Forester, Rough idle and engine loping driving at low rpm

I had a similar problem on my 2002 Impreza RS 2.5 (same engine and engine control system). In my case it was the O2 sensor on the intake manifold. This happened at 34,xxx mi. so it was covered by the warranty. Replacing the part is very easy. (two bolts and a wiring harness). Obviously I would start simple and cheap and work your way to expensive and difficult.
From my understanding its all caused from the engine missfiring. If its been a while or never, I'd change the spark plugs first. (stick with the Subaru Parts plugs, I went after market and the dealer claimed the plugs were not the correct "temperature" and had to pay for the new plugs and install although they did it without my permition. Thats a whole nother story).
Could also be the manifold pressure sensor.
Either 02 or manifold pressure sensor may cause intermitent check engine light.
Where I live Brookline,MA , Autozone will run a free diagnostic on your car by hooking up to your ECU and will give you the trouble codes and possible remidies. Of course there are no guarentee's but it will point you in the right direction.
Good Luck

SOURCE: engine lopes at idle and check engine light on

In this case having the check-engine light is a good thing. Take the car to AutoZone and have them scan the computer for codes - they do it for free, whereas a shop will charge up to an hour's labor. Have them give you a printout of the codes, and post them here as a comment/reply. I can help you define them and see what needs to be done.