Running/Idle Issues

[Sie!]

Morning all,

Looking for a bit of advice on an intermittent issue I've been having with my Audi since the day I bought it (13 years ago). Ive done as much with the car as I can think of, and still I seem to have the problem.

The problem is that on occasion, the car will hesitate whilst cruising (30-70mph) and then when you depress the clutch, the revs drop and die, it is also very hesitant unto about 2500rpm when the issue occurs, but the car will continue to drive so long as you keep the throttle depressed - it makes roundabouts an absolute nightmare!

The car always restarts, then continues to die again.

I would never drive the car when its like this, but it always seems to occur when you're on your way somewhere far, or on the way back, therefore left with no option but to nurse the old thing home.

To all intents and purposes, to me it feels like fuel starvation, but I'm no mechanic or expert by any means.

I should state its a 1985 Audi 80 GL 1781cc Carb.

The vehicle is still running a Pierburg 2e2 (I know, Weber conversion), but the car normally drives 100%, good MPG, smooth, good choke, and the Pierburg works exactly as I should (3-point unit, TTV etc.).

The annoying thing is, somehow the car remedies itself, I don’t know how or what changes, for example I had to nurse it home 80 miles on Thursday, took it to bits Friday, still didn’t work. Saturday its back to normal - its infuriating, but mostly its becoming vastly unreliable and I no longer trust it. When I bought the car it would maybe do it once a year, now its more like once a week, I need to sort it.

So far I have done the following;

Fuel tank out, cut open and cleaned professionally
Fuel Pump
In-line fuel filter
Various rubber fuel pipes renewed

Coil
Distributor refurbed (including hall sender)
Engine retimed
Distributor Cap
Rotor Arm
Leads
Plugs
All carb vac lines renewed

I have repaired various wires to the dizzy and coil I thought were suspect, all to no avail
I have had the carb off, given the chambers and jets a clean

The only things left are the fuel vapour trap and the float needle valve, I have the vapour trap on order and a spare needle valve (is it worth even trying this?).

Also I haven't changed the ignition control module under the dash, I bought a replacement and it didn't work at all, is it worth trying another, can they be temperamental? I assume they either work, or don't.

Is there anything else that’s obvious I'm missing? I would much rather stick with the 2e2 than just jump on a Weber (not least as they’re now 400 quid), but like I say the Pierburg has been superb, and when running is faultless, and I'm not even sure its the culprit.

Any ideas? The issue has been going on for 50k and 13 years, I'm just at the point of dumping it in the garage and leaving it.

Any help, advice or suggestions welcomed.

All the best, and stay safe.

[urquattr085]

Hi Sir

The only thing that comes to my mind (on top of what you have already done/checked) is a vacuum forming in the tank.

When the fault is there, remove the filler cap, see if you hear air rushing in. If so check your tank vent.
Good luck, hope you can sort it

[vagdream]

Could it be a fuel vapourisation issue, does it only happen when engine is warm/hot?

[John.]

As above, was thinking vacuum in tank as it happens on a long run??…….but would think you've checked tank breathing when tank stripped/cleaned??

Have you got correct gaskets/spacers between manifold and carb?

Does it have an anti-dieseling valve on the carb?...…..worth checking/bypassing the wiring?

[vorsprung durch technik]

You say you've had the Carb of for a clean but did you rebuild it and set it up? Thats all i can think is wrong. Buy a rebuild kit and set the carburettors Floats, this is critical to getting the car running right if all else is fine. The floats, float in the petrol bowls and when you accelerate float level drops and opens up the ballcock valve for want of a better word to allow more fuel in. Your float level could be well out. Did you measure it against spec?

[Sie!]

Thanks for your suggestions guys, tank is good, no vacuum forming, carb has been rebuilt, all new gaskets and adjusted so it’s working as it should (warm up/choke 3PU etc.), only thing needing to set is CO when I can get to a meter but it can’t be far off, if at all. Manifold flange is new.

I think I’m gonna go down the route of replacing the vapour trap and control module, other than that I guess it has to be the carb in some way.

If I get to the bottom of it I’ll let you know!

[SwallownAmazon]

Originally Posted by Sie!

I should state its a 1985 Audi 80 GL 1781cc Carb.

That's the same as my first Audi and it developed a similar problem while under warranty. If I remember correctly (it was a long time ago) it turned out to be some sort of diaphragm in the carb having burst and seriously weakening the mixture. 10 minute fix at the dealer on my way home from the office.
It was a company car which I bought for the memsahib when it was replaced and is what converted me to the four rings.

[BackintheFold]

Tank vent is a good call, as is fuel vaporisation.

I had an "Audi 100" years back with similar problem. a new mechanical fuel pump (fitted on the side of the block) was the cure.

Even if you've replaced the pump, it could still be the source-especially if its been replaced with an old pump rather than a new one--- I've had new stuff go wrong before, whcih is a pain-you replace with new and think "well, it's not THAT anyway" and then it is.

To test...um.... try putting an extra length of fuel pipe and a clear fuel filter in -line to the pump and ensure it is working when you have the issue.