P0172 - 2005 Corolla XRS

[DboyNismo]

Hello, I've been getting a P0172 - System too rich code on my 05 Corolla.

I've owned the car for two weeks now, and before I bought it an inspection came back clean. On Friday I got a CEL while in the car wash after filling gas. I thought it was just from the gas cap so I tightened that and said I would take it to an AutoZone to get the code checked/cleared. While all this was happening the car did have a rough idle (around 6-800 RPM), and would usually idle at around 1100. If it tried to drop to 600, the computer would kick it back to 1100 to keep it running I assume.

At AutoZone on Sunday the tech said there were no codes showing. The light was gone so I drove it back to Edmonton that night. On the highway the light came on again. On Monday I scanned the car and got a p0172. I picked up a MAF cleaner from Part Source and cleaned the MAF, reset the ecu. The car idled rough on first start, drove it for 30 minutes for it to remap the ecu, no CEL light. When I got home after the drive it idled at 1,000 without hesitation, 800 RPM with slight hesitation.

Today on the way to work it threw a CEL light. Scanned and same code, p0172 - system too rich. I was thinking of changing the spark plugs as the vehicle has no record of them being changed and it has 160k on it I'm also going to clean the Air Filter as the filter is fairly dirty (A/M K&N pod and pipe).

Any ideas as to what may be causing the code? There is no other codes throwing so I don't believe its the O2 sensor.

[eglove]

If it's too rich it's most likely the oxygen sensor, doesn't have much to do with the air (intake) system

[bourge73]

Sounds like the MAF. Hmmm maybe oxygen sensor as above said

[DboyNismo]

Alright since the MAF is an expensive part, would there be a way to be sure what sensor is causing the problem? I have already cleaned the MAF twice, but I know that cleaning it may not solve the problem. It wouldn't have anything to do with the TPS or anything like that would it?

[AE92_TreunoSC]

Understanding the fuel trim and readings is vital to diagnose the fuel issue.

You need to look at what the long term trim is, and if its affected by temperature by reading the freeze frame.

A dirty MAF will cause the system to run lean typically, due to unmetered air entering the combustion chamber.

O2/A/F ratio sensor can cause rich but is a little unlikely, they usually will trigger a separate code if the sensor is reading irregular high or low voltage.

I would suspect carbon build up in the intake runners and throttle body. Spark plugs are due at 160, so its a good idea anyway.

The XRS's engine does have some issues with oil and coolant consumption, so inspection of the plugs and cylinders will help isolate the problem.

[DboyNismo]

Thanks for the insight ^ The scanner I was using only puts out code data doesn't let me see the LTFT or freeze frame data, I might buy one of those Bluetooth ODB2 readers. Tonight I'll clean the intake and see if that helps.