1990 Coupe 2.3E 10v - jerkiness/poor driveability

[Marcus Oxer]

Dear Listers,

I wonder if you can offer any ideas on the following? It seems to have confounded both my local Audi dealer and a Bosch Injection specialist...

The engine has recently started bucking, or jerking under very light throttle openings - both as I go on the gas, and as I come off it. If I hold the throttle in the same position, the car will continue bucking in a most unpleasant way. Putting my foot down seems to smooth everything out - it's really only a problem if the throttle is held steady with the car under light load.

With the car at standstill and out of gear, I have noticed that if I slowly build up the revs it is quite smooth up to 1800 rpm, at which point it starts to stumble and miss beats in quite a random way.

I have recently replaced everything on the HT side - spark plug leads, distributor cap, rotor arm, in order to cure a different under-load misfire. The spark plugs have just been replaced as part of an Audi dealer service.

My Bosch specialist said that the (non-original) replacement spark plug leads might be causing a problem as he has seen cases where they are insufficiently suppressed and interfere with the ECU. I have reverted to the old leads but the problem still persists.

Reading through the archives, I am wondering whether components such as ISV, throttle position switch, and oxygen sensor could be implicated. However, I am not getting any error codes and also I presumed these are the sort of things that would have been ruled out by the Bosch engineer. He charged me £55 GBP for a diagnostic check, but couldn't find an obvious fault.

Any ideas would be gratefully received!!!

Marcus Oxer
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