Bad running after new head gasket - cause?

[Laird Scooby]

Originally Posted by Miketwovolvos

Assuming good compression and valve timing, plus good injectors (blocked injectors can cause poor idle which goes away at higher revs) the poor idle and lambda light I think are the main clues here. The ECU sets the idle and the fuelling based on the TPS and AMM amongst others. I have had weird stuff happen when the AMM was faulty or the 6 connector block fit was poor..I would change the AMM and check the resistance of the TPS...also, if it is over fuelliing then I would check the resistances of the temp sensors in the block...they can go bad and tell the ECU it is 30 degrees below..FInally, if you could get its emissions checked...it could be overfuelling due to a leak in the manifold (or elsewhere) that the garage replaced..oxygen gets in and the Lambda sensor reads it and the ECU overfuels...esp if it is in intermittent leak...good luck with it...the AMM is self cleaning so spraying stuff into it is probably unnecessary.
Check fuel line pressure also..a failing pump could cause some issues, but I think its more likely to be the AMM and/or the block sensors
Mike

It's fixed - it was the MAF in the end. Also for future reference, the TPS isn't a sensor on these, it is two switches, one is made on a closed throttle (idle) and the other is made on a WOT (Full throttle) with nothing in between.