Every now and then (getting more frequent) I get a puff of black smoke on startup only when engine cold, after eng has been running for a 5 seconds.ie Eng starts normally, no smoke (ie probly not leaky injector) then revs drop, black smoke, revs pick up smoke clears revs drop black smoke this goes on for ablout 20secs until eng warms or I boot it a coupla times.

Dont think its a leaky injector, its more like what a carburettor engine would do if the choke was put on for too long then released then put on again. I think something is trying to put fuel in to compensate for a drop in engine revs when cold .

IAC valve or Maf sensor or Oxygen sensor?



PS CHEAP MAF SENSORS: Apparently Maf sensors are same as used in BMW and common to many European cars inc VW with slightly different part no.

"These Bosch MAFs are pretty common, basically all the European manufacturers use them, or a similar part. In fact, the exact BOSCH part number on my 04 D2 MAF sensor housing is 0 280 218 010, and is also used on BMW and Mercedes cars. The M5 in particular. Yes, that's right, the 03-04 D2 and 99-02 P38 is the exact same part as a BMW M5.
The Bosch part number on the sensor insert is F 00C 2G2 029. It turns out that some of the BMW M5 guys are using the sensor insert from a VW, F 00C 2G2 032, it's cheaper, and the calibration difference is reportedly 4%. The computer can easily compensate for that. The only other difference is the 029 has pins to secure the connector, the 032 is missing the pins. The connector fits, but is only somewhat secure. Some are running just with the friction from the pins, some are tie strapping it down. I found a cross-reference somewhere, and there are no cheap MAFs which use the 029. The 029 is used in all BMW's, Porsches and Rovers.

The 032 part comes in a MAF for a VW Golf, and in fact is quite cheap due to a class action lawsuit. Apparently they actually sued because the sensors fail so often, and they (Bosch, VW, Dealers) were making so much money on it, they dropped the price."