2nd Gen R56 P2188 code causes?

Not too long ago I took my 08 MCS to Best for an oil leak, and a minor CEL that was throwing that code (System too rich at idle)

The oil leak was taken care of (vacuum pump), and they cleaned the contacts on the downstream O2 sensor to get rid of the code and told me that if it came back, that we’d just need to replace the downstream sensor.

Given that a sensor replacement is something I can do easily, I went ahead and got a new pair of sensors from Rock Auto (Delphi brand, with the OEM part numbers). I’m currently unemployed so money is a bit tight, and while I did not get the cheapest sensor, I did not get the most expensive either. Having consulted with a friend who is a professional mechanic himself (though mostly for American cars) I felt this would be and OK thing to do.

I was able to replace the upstream sensor no problem, but due to Ohio road salt, did have to cave and take the car to a nearby garage to get the downstream sensor installed.

The CEL cleared, and the car runs fine, but every so often the CEL with the same code returns. It can be after a day or two, or after a week. I consulted briefly with my mechanic friend again (I try not to abuse our friendship for professional advice), and he wasn’t sure that it was a consistent enough error to really know what might be the cause.

So far I’ve just been clearing it and going on with my life.

So, do I have a bad sensor? Should I look at something else? I’ve seen where a bad Mass Air Flow sensor can cause those kinds of codes in other cars, but if that’s the case wouldn’t it show as an upstream failure?

Ideas?

 

It has been a while, probably about 60k come to think of it.

 

Cool, Thanks for the advice. As soon as I have money coming in again it'll be off to get a good blasting.

 

So here’s a follow up to this - just in case this information is useful.

I’m still unemployed and on a budget, so finding the money for a walnut blast is not in the cards at the moment BUT I do appear to have resolved the issue for now.

Prior to getting this code, I’d been buying UDF gas rather than my usual Shell. It was still Premium grade, but it’s a lower quality fuel, so that could have been a contributing factor.

I put 5 oz of SeaFoam in the crank case, and some STP Injector Cleaner in the tank, and used MAF Cleaner on the Mass Air Flow Sensor, reset the ECU using my ODB reader and cleared the codes one last time.

ThenI gave it the old “Italian Tune Up” and ran it at high revs (basically third gear on the highway) for long times and let it get good and hot. I did this for about a week, making sure that once the engine was warm to just flush gas through the whole thing.

Since doing this, and the entire time after the SeaFoam, Injector cleaner, and MAF Cleaning, I’ve not had the code come back.

Is it a long term fix? Probably not. But it appears the Snake Oil isn’t usesless, and the car is running fine for now, so I’ll take it.