Engine shuddering at idle and low revs

[PeteK]

I have just returned from a longish (100 mile) journey in my 2004 Passat 130 Tdi and it has developed a fault towards the end of the trip. I noticed when slowing down towards a junction that there seemed to be a light shudder through the car, however I thought it was the road surface and carried on driving as the car seemed fine. When I next came to a stop at a set of traffic lights, I find the engine is vibrating badly. It feels almost as though something is badly out of balance and is wobbling the engine about quite badly. I drove off as normal and the car feels fine accelerating through the gears and at a steady speed - the clutch also engages smoothly as it normally does and the car is perfectly smooth above 2000rpm. My initial thoughts are that the dual mass flywheel has failed - the vibration is the same whether the clutch is engaged at idle or not and the vibration cannot be felt through the pedal or the gearlever. However i'm now not too sure as I would have thought that the vibration would be worse at higher revs which is not the case? I never noticed a drop in power, however I didn't really push it after it started vibrating - would a failed injector loom cause these symtoms? The engine code is AWX and the car has done 169k miles; clutch and loom are both the originals. Any input would be appreciated guys, I will plug in VCDS tomorrow to see if there are any faults logged (which I doubt as there are no warning lights on).

Many thanks,

Pete

[PeteK]

Well i've just started the car up again from cold and it now feels fine - very strange! I've checked for codes and there is nothing stored for the engine ECU. I've taken it for an 8 mile drive and it's still fine, although i'm convinced the engine feels a tad lumpy at tick over which can be felt through the whole car but certainly nothing like it was last night.

I think I will take the precaution of replacing the injector loom once my local specialist reopens tomorrow as it would appear to be an intermittent misfire rather than a mechanical failure.

[PeteK]

I've just checked with the local dealer on price and availability of the loom and have been quoted £68 + vat. Does anyone know of a guide to replacing this, or is it relatively straightforward - would a new cam cover gasket be required? I might try and tackle this myself when i'm off work next week. The local dealer also advised me that they sell a lot of injectors for this model so that could also be the problem. He laughed when I said there were no fault codes logged and assured me I shouldn't trust these '3rd party' diagnostic programmes as it was likely that the VW diagnostic machine would find a fault code that VCDS wouldn't pick up - not too sure on that as I thought it would log the fault codes in just the same way?!

[martin1810]

It's a straight forward job. Easier if everything is warm. Both old loom and new one. Talk of injector failure on this engine is nonsense. The injectors are pretty good and last well. VCDS is not quite as good as the VW tool but it is so close you almost can't tell the difference. When iit comes to fault codes, there is no difference. The best way to spot a loom problem is to log engine measuring blocks for the injectors. Fault codes only show if the fault repeats too often or is severe.

[PeteK]

Thanks Martin, after doing some searching on here I found this thread which has some really useful advice.

https://www.vwaudiforum.co.uk/forum/s...+wiring&page=2

With regards to the measuring blocks, I took a quick look at this yesterday. I was expecting to find a channel which showed the amount of fuel injected by each individual injector; however all I could find was group 13 which shows something to do with the smooth running injector values. Can you suggest any other channels to log? I've attached the values I logged yesterday however it may not show any problems as the engine was only just warmed up; the lumpy tickover only starts to appear after the engine has run for a while.

Thanks again for your input.

[martin1810]

The MAF and EGR figures for your scan don't make sense. Have you done anything to the egr. If you haven't I would take the big air pipe off and make sure the egr valve is shut. It's the small valve in the bottom, not the the bog flap. If it is shut I would then pull off the vacuum pipe for the egr and plug the rubber pipe with a bolt. Run a new hot engine scan, through the revs as before idle to 4000 ish. Then we can see what your MAF is doing.

[PeteK]

The EGR has never been touched since i've had the car Martin and is completely standard - the only thing I had done is have the car remapped to approx 165 / 170 bhp which I can put back to standard tune if required (it is a proper remap - not a tuning box or cheap resistor job!). I'm not too sure how to interpret the figures to be honest - however I noticed the MAF expected and actual figures seem to be quite similiar most of the time which I thought was ok. I will do another log when the engine has had a good run, however due to work may not be able to do this until the weekend now. I will also check the EGR is not stuck open.

Other than a slightly lumpy tickover (which is nowhere near as bad as the other night) the car is running like a dream. I've just done a 55 mile journey from a cold start on a mixture of motorway (10 miles) and the rest A roads and it has averaged 53.5mpg on the trip computer (which in real terms will be about 51mpg as it overreads by 5%). It still pulls as strongly as ever and feels really smooth. I'm going to order the injector loom tomorrow as I think even if that is not at fault, at 169k miles it is best to replace it anyway.

Thanks for your help so far - I will provide an update as soon as possible.

[martin1810]

That was going to be my next question. The egr will be ok. The remap has changed your MAF requirements which is why the MAF and egr figures look so odd. In that case I can't see anything wrong with your log.

[PeteK]

Thanks mate, at least that is reassuring! I phoned another main dealer today as I thought the original quote of £68 + vat sounded a bit high after reading some other threads on here; they have quoted £43.19 + vat and confirmed it is part number 038971600 which checks correct with VAG CAT. I have ordered this and it should be in tomorrow - weather and hangover permitting, I will have a go at fitting it over the weekend and report back how I get on.

[PeteK]

Got the injector loom today, I was expecting a big bundle of wires but there is not that much to it! It was looking doubtful at one point as the dealers were closing at 4pm and I was unable to get there before this time - however the parts manager offered to go out of his way and deliver it to my door on the way home at no extra charge; a massive thank you to Corkhills of Southport for their fantastic customer service. I can't wait to fit it now to see if it cures the rough idle. I've also treated myself to a Pela 6000 oil extractor pump today as I plan to start doing my own services - the only thing that put me off before was the difficulty in accessing the sump plug due to the plastic underguard however with the pump there is no need to remove the sump plug.