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Discussion Starter · #1 ·
I have a '99 528i running really rough. It even backfired a couple of times when cold. Current codes are p0170, 0173, 1188, 1189, 0300, 0302, 0306. I know the first 4 are fuel trim related and the other 3 are misfire codes. I just don't know where to start looking. Could the misfires be caused by the fuel trim problems? Any help would be greatly appreciated.

Premium Member
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P1188 is BMW's fault code 227 which is saying there is a deviation in the fuel mixture between cylinder 1-3. This is a code only on M52/S52 engines running with a Siemens MS41.1 or MS41.2 DME. Some of the problems that can cause this are:

-Vacuum leak (intake gasket, crankcase breather, etc)

-Defective fuel pressure regulator

-Wrong MAF

-Defective MAF

Fault codes P0170 (BMW fault code 26) usually states there is an issue with your oxygen sensors control adaptation (injection) in bank 1.

P1188 and P1189 and P0170 are typically MAF sensor issues. Because the MAF is listed in the original fault code of P1188 I would look there first. However, don't rule out possible oxygen sensor failure.

The other codes regarding misfires are a result of the fuel related issues from the first 4 codes. Does the car misfire when warm and at idle, does it misfire when it's cold and idling, or does it misfire when accelerating. P0300 is a code for multiple random misfires and some of the areas which can cause this problem are:

Faulty spark plugs or wires
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector(s)
Burned exhaust valve
Faulty catalytic converter(s)
Stuck/blocked EGR valve / passages
Faulty camshaft position sensor
Defective computer

Overall, I'm leaning to a possible MAF sensor issue being your best case scenario and faulty O2 sensors being your worst case scenario. Depending n your mileage, and assuming your O2 sensors have never been replaced I would suspect an O2 sensor almost immediately. I would also look to see if there isn't a vacuum leak as well. I hope this helps you out to an extent and best of luck! :thumbs
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