Car runs rough when cold, fine when up to temperature

[tomgtturbo]

Hi all,

My BAM engine Cupra R has started to run rough/lumpy when cold.

It starts first time and idles perfectly but when I start driving it seems lumpy and feels like a light kangarooing.

Once up to temperature it runs spot on and the issue goes away. Boost fine etc etc.

Unplugged the MAF today and it does seem a little smoother.

Could the MAF cause this?

 

[mty12345]

Unlikely, as unplugging the MAF also disables lots of other things like fuel trims and O2 sensors. The car basicly runs in a 'backup mode' and just guesses at the fueling etc. The unplugging the MAF thing is a bit of an urban myth/old wives tale, but it's probably made Bosch a **** load of money over the years.
m
Far more likely, is that one of your PCV hoses is split or has popped off. That will often cause lumpyness at low RPM as the ECU can't get the fueling just right, but it will typically dissappear higher in the rev range, as the effect much smaller when the system is under boost. Most of the PCV hoses are located above the oil filter area and under the inlet manifold, also there is a large one coming out of the cylinder head. Give them a good inspection and have a good feel around for splits, some only show up when you give the pipe a gentle squeeze. I'd say there's a 90% chance that's what the problem is.

 

[Jay20VT]

Moisture somewhere?

 

[andylong]

If you are confident it is temperature related, check the temperature sensor and related wiring. It's easy to relate issues to unrelated things masked by manner of driving, so it might seem temperature related even if it's not.
Do the easy checks first as above.