Engine, 2.5L, idles rough, surges, and stalls. Replaced MAF & MAP and this did not correct the problem. Disconnected the MAF and engine runs smoothly at idle. Once MAF is reconnected problem returns. Is this a faulty ECM/ECU or could the O2 sensors be faulty.
Did you retrieve the trouble codes prior to working on it?
Reinstall everything and clear trouble codes. Run engine and when Malfunction Indicator Light turns on, retrieve the trouble code and let us know what it is.
December, 31, 2012 AT 1:54 AM
I retrieved the following codes, P0171, P0173, both codes report lean STFT from the 02 Sensors. Both sensor banks show similar readings. It occurred while driving a about 60 mph, with engine temp 186 degrees. After unplugging the MAF sensor I received a P0102 DTC, which makes sense because it has been disconnected.
I have done the following checks: 1. Sprayed carb/choke cleaner on all vacuum lines and no leaks detected. OK
2. Check fuel pressure (4x) on incoming side and got stable readings close to 40 psi. OK
3. Replaced PCV Valve. OK
4. Replaced fuel filter. OK
5. Did compression test on engine, all cylinders approximately 200 psi. OK
6. Inspected, cleaned, and regapped spark plugs. OK
7. Replaced MAF, and MAP. OK
8. IAC inspected, very clean, and appears OK.
9. ECT sensor shows good temperature reading when scanner is linked.
Additional information: Engine is completely stock, OEM.
When I unplug the MAF the engine runs significantly smoother. When I plug the MAF back it it runs extremely rough, surging, and eventually stalls.
I don't have spare ECM to try and switch to see if it is the problem. I am considering based upon mileage to change the 02 Sensors and have the ECM rebuilt and reflashed.
Does this sound like a logical plan based upon my observations?
December, 31, 2012 AT 1:18 PM
From the diagnostic procedures for P0171, I believe you have missed out one more possibilities and that is the fuel level sensor.
P0173 is not found in our database, only P0171, P0172, )P0174 and P0175
December, 31, 2012 AT 7:38 PM
DTC P0173 was incorrect is was supposed to P0174, my apologies. In reference to your checking the fuel level sensor, in the instrument panel gas gauge appears to functioning correctly do I still need to eliminate this possibility?
Thanks for the help.
January, 1, 2013 AT 2:37 PM
If you have a scan tool that can test the level sensor, that would be easy.
When you can't find any problem with basic checks, we have to look at all possibilities to avoid making unnecessary parts replacement.
Lean running conditions are never easy to diagnose. You mentioned replacing the MAF, was it a used or new unit? Did you try cleaning the MAF?
Did you check for leaks between the MAF and throttle body?
January, 11, 2013 AT 1:12 AM
I replaced the MAF with a new unit. I did try cleaning it, the old one, before purchasing a new one. I checked for leaks between MAF and throttle body by spraying carb cleaner with no leaks detected.
I have since replaced the ECT sensor and all six fuel injectors.
Retested fuel pressure and readings are within specifications.
When I unplug the MAF sensor the vehicle runs very smoothly but idle is slightly elevated and adjusts slowly. Engine always starts right away with a smooth idle and within a matter of a few seconds starts idling rough, with little throttle response, and usually stalls.
I recently noticed that the IAC valve is very hot to the touch, this is when the engine is warming up and the intake manifold, where it is mounted, is still quite cool. Do you think that the IAC valve is faulty based on this. I have tested the resistance/ohms and they are within specifications. It is also receiving power. How is the solenoid supposed to move when the key is turned on and off? The IAC valve solenoid does show movement.
January, 22, 2013 AT 1:36 PM
The IAC controls the idling speed and since it is erratic and stalls it is possible it is not working within specs.
It works on electrical current passing through a coil so heat is expected.