I have a 2003 Disco, 4.6 NAS engine w/ 83k on it. Have a new MAF, plugs, Magnecor wires, clean IACV, TPS, new alternator, new cooling hoses, new thermostat. It has been Sea Foamed. The engine runs great at cold start, smooth idle, plenty of power. I can drive the truck for hours and it will run great. But when I turn it off for awhile then drive it again, the truck seems to have less power. It will still idle smoothly but it's almost as if it's running too lean or the Bosch Engine Management has gone into default mode. Is there anything in the Bosch engine management that can fail or change parameters to a less than optimum setting only when warm after a restart? I am throwing no codes. Also, if I wait until the next day and do a cold start, everything will be fine again.

 

Well first of all why did you replace all the parts that don't go on a 2003 disco Two? Sorry but MAF on those don't go. earlier disco 2 do but that is for a 4.0. Secondly alternators rarely go on bosch. Very rare. the batteries cause issues. TPS, not at all unless disconnected. I would bet you used an aftermarket maf sensor and or other parts that are causing the issues. Trust me, ten years in the business and OEM has never failed yet. Aftermarket, all the time. Enough that you waste more money diagnosing the cheap part then the cost of a new part.

 

What??? MAfs do go on these and my truck ran light years better after installing a new Bosch MAf. Could be the PO ran a K&N, who knows. The alternator was squeaking loudly because the PO steamed the engine numerous times. To clarify - I cleaned the IACV and made sure the TPS was not dirty, they are still the orginal parts. Any other specific suggestions to help? I just need an answer to the actual question I posted.

And regarding MAFs - Bosch MAFs are notorious for deteriorating operating condition after 30k or so. Do some google searching on BMW 540 forums - they use the same MAF. When the MAf deteriorates it will not throw a code, it just does not work in optimum condition. MAF Cleaning also will accelerate the degradation of the MAF. DiscoMike has always pointed this out and I learned from experience he is right. The MAF is probably the first part I would recommend replacing if you can't track down the reason for your poor idle condition. It's $139 bucks but it saves a lot of headaches to just replace it IMHO.