A6 poor running

cantdecide

my '98 A6 2.8 has intermittant poor running/ idle.

it has been fully serviced recently but since i got it in March it has had rough idle but not too bad. my mechanic cleared a lot of faults from the obc and after a fortnight none had recurred which he was surprised about but that was about 6 weeks ago.
there is a number of fuel related problems I've had- never gotten around to replacing the temporary filler cap for correct one. i have a dicky fuel level sender, it reads approximately 1/2 way for the middle 80% of the fuel load. i suspect it was regularly run out of petrol before i bought it. i have a noisy purge valve which is due to be replaced soon.



at worst it hunts from maybe 800rpm to about 1050rpm for maybe six or seven times before settling on uneven idle again.

sometimes it idles reasonably well at 800 rpm which is too low.

most of the time it idles ok at 900rpm but seems to miss occasionally.

sometimes it has a fairly substancial miss when driving like a kick which will happen maybe every 1/2km. this last usually for a day.

in general i find it hard to change gears smoothly and is very jerky in low gears and in especially traffic.

I also suspect the revs linger too long when the throttle is lifted.

I've noticed that when hot, it starts on the first 1/2 turn which seems oddly quick. it also 'pinks' noticably and the revs pick up slowly

fuel consumption is about 27mpg which i think is about right but i'm not sure

Wishbone Ash

cantdecide wrote:

fuel consumption is about 27mpg which i think is about right but i'm not sure

27mpg seems very good for a 2.8!

cantdecide

Papa's 3.0 auto gets about the same mpg...

Wishbone Ash

cantdecide wrote:

Papa's 3.0 auto gets about the same mpg...

Diesel?

cantdecide

both are petrols

Elfish

Reckon it's dirty throttle body. Had exact same problem with a golf. Fixed with motorbike carb cleaner spray. What sort of mileage is on car?

cantdecide

110,000 miles

dumb question time- what is the purpouse of a throttle body and is it hard clean or hard to get access to? I've used fuel treatment but has had no effect.

mike65

cantdecide wrote:

110,000 miles

dumb question time- what is the purpouse of a throttle body and is it hard clean or hard to get access to? I've used fuel treatment but has had no effect.

The throttle body is where the air flow is regulated, if its full of crap the butterfly value won't operate quite as intended. The clearance tollerances within the body are important so a build-up of sooty gunk can be the difference between smooth and rough running.

Mike.

cantdecide

how troublesome is this to rectify?

mike65

Not sure I have an A6 but the 4 pot and I've never needed to investigate that aspect. to get at the chamber you might have to unhook the fuel injection system but as I don't have a picture (I googled but can't find one) its hard to say.

You could try e-mailing club-audi@yahoogroups.co.uk

Mike.