a6 2.7t quattro, judder at constant speed, part load.
Apologies in advance. As usual for new users, I'm here with problems, not solutions.
I have an old 2000MY A6 C5 2.7t quattro. It idles, runs, goes and drives very well except for one small annoyance which I've run out of ideas for.
The symptom is a slight judder when cruising at 80mph (3000rpm). It doesn't feel like a missfire, the car just stutters ever so slightly once ever 10 seconds or so, passengers probably aren't aware of it, as it feels like riding over an uneven section of road.
There is no change in rpm with this and it happens with and without cruise control.
Another symptom which may be related, or may be different is a tendency to judder harshly if changing gear around the turbo spool up point of 2.5krpm.
The car has 3" exhaust front to back, sports cats and downpipes, high flow intake filter, one step colder spark plugs, a remap to about 270ldft and a fast road clutch.
This minor annoyance has started after fixing a nasty missfire at full load caused by the remap. The cure for the missfire was to put in the colder spark plugs. ot pull down the cylinder temperatures. The missfire was fairly harsh, is it possible I have done some damage to the haldex, or other part of the drivetrain? Or is this a common symptom with a known cause? I've certainly seen it listed as a problem elsewhere, but never seen a solution.
PS - The car has also had a recent cam belt service, new lambda sensors, crank sensor and had a faulty fuel injector connection repaired. This is the first time since the cam belt service the car has run close to right. Is it possible the cam timing is out? I would have thought that the car wouldn't even run if that was the case.
Last edited by sanctum; 5th October 2010 at 15:14.
Turns out the problem was just spark plug gaps.
I had gapped the copper plugs quite generously, after reducing that gap down to 0.7mm(0.028") the above symptoms have gone and the car runs more smoothly both in cruise and overrun.