I've just bought a 1996 Audi A4 TDI (reading 69,000miles)which pulls like a train and drives really nicely but once it's warmed up the idle becomes rough. It's as if a pot keeps missing though it never stalls. I've changed all the filters and tried injector cleaner but that doesn't seem to have made any difference. On the tacho the tickover speed reads about 840rpm - is that a bit slow? If I could speed up the idle maybe it would smooth out. Any ideas welcome.
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does the car smoke? also i assume that it a 110tdi not a 90.
these cars do suffer from mass airflow meter faliure. it is fixed to in air intake pipe just up from the airbox. idle speed sounds a bit low but im not sure. i would get the cambelt timing checked and get the injectors reconditioned. just cos its got low milage dosent mean that they are ok. diesel combustion melts the nozzle on the injector so that instead of a nice spray pattern one could be dribbling excess fuel that the engine dosent need. when the car is cold you wouldnt notice it as the ecu gives the car a enriched mixture to counter the effects of cold engine internals.
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Thanks for the info
The engine code is 1Z. In the Haynes manuel it says it's the 90bhp version. It smokes white at startup but seems fine when warm. When cold it cranks for a few seconds before firing. (I'll check the glowplugs)
I've been reading about the airflow meter and how often they fail. As well as the rough tickover it also doesn't pull willingly over 3000rpm - is this another symptom of a u/s MAF?
Up to 3000rpm the engine pulls really well.
PS Although the car reads 70,000 miles I'm wondering if thats correct. Do they get clocked very often?
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could be. try to find a fuel injection specialist with either vag.com program or a vag1552/1551 machine. they can then interigate the ecu for faults. they may be there but not bad enough for the fault light to come on. is it flat over 3000rpm?
does it smoke badley(sooty) under hard acceleration visable in rear view mirror? one thing to try is that in the pipe between the airflow meter and the inlet manifold(plastic pipe) there are two sensors air temp and boost pressure if i remember right try cleaning the pipe and sensors with solvent (white spirt) and a soft paint brush as oil contamination tends to collect here and affect the sensors output. saw this in vw motoring so try this.
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If you are cleaning the mass airflow sensor, be careful! They are very fragile. I damaged the maf from my Vectra td when I carefully cleaned it with isopropyl alcohol. It might be worth submerging it, but I wouldn't touch the metal sensors even with a soft brush etc. The replacement cost me £160, be warned!
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