PD 130 AWX engine stumbling when cold

[negev]

I've read endless threads about this online but never found a solution. Was talking about it with a colleague and wondered if since it's so common, whether somebody else on here has run into the same thing and found the solution.

Basically when the car is cold it idles fine until it's rev'd or driven a few feet, then stumbles (rev needle dips) every 2-3 seconds a handful of times then settles down. If rev'd again it will do it again.

After 5mins of driving it's perfect and doesn't miss a beat.

So far I've:

- Changed the injector wiring loom
- Had all four injectors removed, tested and refurbished
- Cam lobes were inspected when the injectors were out, diesel specialist said the cam looked brand new
- Changed the EGR valve twice
- Fuel filter, various services
- Taken it to four garages and a VW specialist, nobody knows what's wrong
- Scanned for codes many times with VCDS - car gives nothing. Graphed as much data as I could but all I could see was symptoms, nothing that indicated the fault.

Also if I start with the aircon compressor is off the fluttering isn't so pronounced but is still there.

[Crasher]

It is not possible for anyone except the Bosch factory facilities to correctly rebuild and calibrate PD injectors so unless they are Bosch exchange units I would not trust them. Were the injectors set up in the engine, dialect in and their max lift settings performed? Has the cam torsion value been checked to make sure it does not exceeded +/- 3 degrees? The AC being on places a load on the engine which helps stabilise it if the feeling is rough.

[negev]

It is not possible for anyone except the Bosch factory facilities to correctly rebuild and calibrate PD injectors so unless they are Bosch exchange units I would not trust them. Were the injectors set up in the engine, dialect in and their max lift settings performed? Has the cam torsion value been checked to make sure it does not exceeded +/- 3 degrees? The AC being on places a load on the engine which helps stabilise it if the feeling is rough.

The injectors were done by AP Diesels - 403 Forbidden

I have no idea exactly what they did, the invoice just says they reconditioned the injectors. I think I checked the torsion value with VCDS a few months ago and it looked within spec. AC being on makes the rev dips more pronounced rather than less.

I'm skeptical it's anything to do with the injectors, after a few minutes of driving the car runs perfectly.

[Crasher]

The operation of the injectors in the fuel they deliver is everything, there is nothing else.

[negev]

Ok well you probably know more about it than I do. The guy at AP diesels said it seemed like an electrical problem.

[Crasher]

It could be, an electrical problem in the operation of the injectors.