Missfire, popping, cutting out.

[Texi]

Unsure which thread applied. 2000 Golf Auto cabriolet 2 Litre with AWF engine, Single port Petrol injection.
The car seems to fall between being a Mk3 and a Mk4. So I guess it's a Mk 3.5 ?? Hopefully some kind sole will place this thread in the right location if I've got it wrong. (Sorry).

The car suddenly developed an erratic running nature about a month ago and has been off road since. The running weakens until cutting out altogether. Attempting to rev the engine results in appalling spluttering, backfires, popping and general erratic responses until it dies. Seems to start okay but continues to have this tantrum.

I’ve had advice from various sources (friends and professionals alike) that include, contaminated fuel, worn rotor arm and damaged distributor cap, blocked fuel injectors and even one mechanic insisting there was probably something bunging up the exhaust pipe.

I drained the fuel tank (since my other car, a jeep, started to display exactly the same symptoms having filled up at the same station but 22 days apart), changed the fuel filter and put in fresh petrol. No improvement. Discovered a leak in the brake servo vacuum pipe. Disconnected it from where it pushed onto the stub pipe on the inlet manifold (Plenum chamber?) and whilst holding a finger over the stub pipe, started up and noticed a noticeable improvement. The leak(s) in the brake servo pipe have been sorted and the limited improvement lasted long enough to drive the car to a local independent specialist VW garage. They identified error codes relating to the (TB) Throttle body and re-set those. Still running badly. They turned their attention to the Distributor cap and rotor arm and fitted new ones. Still no improvement and reverted back to the TB. Trouble is VW supplied replacement costs over £800 so I supplied one found on eBay. It’s not a VW genuine part but was claiming to be totally ‘Compatible’ with part numbers correct. No doubt made in China or somewhere. Garage’s VAC system couldn’t read or do a set-up so it's useless and heading back for a refund. The old TB has been re-fitted. The garage are still trying other diagnostic tests but remain leaning towards having the TB replaced.


With all the mention in other similar threads of this sort of problem being rectified by replacing the ECU relay (30 – not the same apparently on this VW model), or the crank speed sensor (Impulse sensor on this model), and Coil, but my garage don’t regard these components as being suspect.


Before I hear back from the garage and possibly having to have the car returned to me un-repaired (because I simply cannot afford a new TB), I thought I’d post and see if there were any ideas from the ‘good’ skilled fresh minded folk here.

[zollaf]

sounds like an air leak somewhere.

[Texi]

Sounds like it to me too, Zollaf. Of course the TB could be faulty or simply worn which would also be where the air leak is coming from. Wear probably wouldn't explain why there was such a sudden change though. failure of the ECB within the TB might explain it though.

Strange thing is that since owning the car (bought in Dec. '13) an engine management warning light refused to stay off for long after re-setting. Fault code indicates an air leak (weak mixture) but there was no detrimental running problems until this sudden plethora of bad behavior. The previous owner had just about everything in the engine sprayed with sealant after numerous repairs and parts replaced in an attempt to have the warning light stay off but I guess he just gave up since it ran fine. However, I found this crack in one of the unions of the brake server vacuum pipe and bound it up well. The engine continued to perform perfectly well with the exception of a gearbox problem which have since been rectified (see other posting if interested). Everything has been honky dory until suddenly a month ago. Like I explained in my original post, the same vacuum pipe to the brake servo has once again been sorted with a much better repair since VW can't identify the correct pipe for it to be replaced - such are the problems with a cross-over model such as this car.
Yes, an air leak.... but where? No-one seems to have a clue where. If the car comes back to me, I can spend the time removing and re-seating the two part inlet manifolds but my gut tells me it's a component failure to blame for such a sudden change in it's performance.