'04 2.0 GTTDi (BKD) rough idle, warm start and small hesitation, help!

[Uncle_Ben]

Hi All,

Well I'm a newby here and have tried pretty much all the usual suspects to try and solve this, temp sensors both OK, MAF is OK, cleaned EGR, battery voltage fine, even had a full diagnostic and nothing at all showing on the injectors.

The symptoms - Starts from cold perfectly, after maybe 30 seconds she starts to run lumpy on idle, like a misfire every second or two, engine shakes and can be felt in the cabin. When the engine is cold, she almost hangs back ever so slightly when you put your foot down, but then she flies as she always has. When the engine is fully warm (like 15 mins driving), the lumpy idle has gone completely, as has the slight hold back on power. Turn her off, start again and she cranks maybe 10 times before she starts.

The odd thing - Turn the AC on when she's lumpy, and the rough idle stops! Raise the revs ever so slightly, like 50 rpm using the throttle, lumpiness disappears also.

My thoughts so far - Had the cambelt changed a whil eback, could the timing be adrift? Battery was a little tired over winter, but now 12.6 volts at static, seems OK? OBD scan results in code 17058, glow plug issue... Could this possibly result in a lumpy idle? I've read stories of the BKD using the glowplugs until the engine is upto full temp, like the preheat stage and then a maintain stage, until the engine is fully warm, would this explain why the lumpiness goes after she is fully warmed up?

Another observation - She seems lumpier at idle the warmer the external air temperature is? She also runs exactly the same with the MAF unplugged, is this normal?

Any suggestions greatly welcomed... Ooh, she has 128k miles on the clock if that helps.

Any help whatsoever greatly appreciated.

Cheers

Ben

[nevo]

Firstly uncle ben has she had the free software update,would be worth calling in dane and checking,now the poor warm starts,disconnect the temp sensor when she's warm and see if that makes it start first time,there is a big issue with warm starting caused by either the battery a bit weak and or the starter motor you'll need to check the cranking speed,unplugging the temp sensor simulates a cold start,try that and see how it goes.

[Crasher]

The BKD can be very prone to poor idle with nothing you throw at helps. A common cause is the dual mass flywheel failing but one I did the customer was really irritated by the lumpiness and persevered with it and we took the plunge on new injectors which cured it. The poor starting also points towards leaking injector seat faces.

[Uncle_Ben]

Cheers both for you replies.

I can't say that I've had any updates etc on the ECU so I shall try Dane, ta very much for that!

As to the DMF, I had a new one of those last year and that felt completely different when that was on it's way out to what i am experiencing now, the DMF misbehaved all the time too, not just on cold as she does now. Hope it isnt the DMF again though, that wasnt cheap!

I've already tried the unplug coolant temp sensor trick and that proved no change in the way it started or ran I'm afraid, just call me lucky :-(

Nevo - When you say check the cranking speed, do you mean how quickly it turns over? Sorry to sound a bit thick!

Update - Changed the faulty glow plug, issue still remains!

Update2 - Had a diagnostic ran on it last night, when at full running temp the ECU reckons coolant is 83 degrees. Unfortunately I couldnt check her whilst the engine was cold as had to travel for the diagnostic. After 25 mins running on the spot, this had only changed to 85 degrees (temp dial on dash remained on 90 all the time). is this normal for the engine to not be getting really hot, or could this point to a tired coolant sensor? The chap that ran the diag said whatever the issue is it isnt going to kill the engine, as the car is ECU is trying to sort it out by adjusting fuel etc, that said it seems to be getting worse :-(

Should I try the same when the engine is cold? I think I may have to bite the bullet and take her to local VAG specialist who also has a rolling road, to see what's going on.

Thanks for taking the time to replay chaps, it's very much appreciated.

Cheers

Ben

[nevo]

The ecu update was about 4 years ago,don't know how long you've had it,cranking speed is as you've said turning over on the starter,but if you've tried the unplugging the temp sensor that eliminates the starter being slow,I think the ecu temp and sensor discrep is normal,incidentally how old is the mass meter and where did you source it? anyway if you can get it in vw for a freebie they'll be all over it looking for work,then go away and mull it over.

[nevo]

Just an aside crasher can those seats be recut and oversize seals be installed?

[Uncle_Ben]

The ecu update was about 4 years ago,don't know how long you've had it,cranking speed is as you've said turning over on the starter,but if you've tried the unplugging the temp sensor that eliminates the starter being slow,I think the ecu temp and sensor discrep is normal,incidentally how old is the mass meter and where did you source it? anyway if you can get it in vw for a freebie they'll be all over it looking for work,then go away and mull it over.

Bought her from a local garage 4 1/2 years ago, I'm guessing all engine parts are original as she came with a load of receipts for work done, none of which was anything engine related other than the cambelt (done just before I bought it, roughly 80k miles) The MAF is probably the original, I would say. I do have a gubbins on order that can read the realtime KPA data from the MAF, would this be of any help? I did notice that she runs exactly the same with the MAF completely unplugged? Is this normal?

[nevo]

well if you unplug it there is a default program in the software so as you suspect it should tickover ok,the software update wasn't widely known, vw were just doing it as they came in for service,except for the forum readers, so it could have slipped through the net,as for the maf I would have just changed it for a oem one at that mileage,interesting you say it disappears on switching the ac on because the software does increase the rpm to compensate for the extra load.

[Crasher]

Just an aside crasher can those seats be recut and oversize seals be installed?

No, the standard procedure is to fit new injectors or even just swap them around. I have only ever seen extremely light marking which literally polishes off but I do know of instances that have required a new head. Someone should make a seat re-facer like on certain Mercs. There is no base fire ring though, it is direct to head which is a daft idea and was bound to cause trouble, VAG cost cutting **** up AGAIN!

[macca2008]

I had a similar problem,a new battery sorted it out.But I am aware the issue can be caused by a number of things.
A relatively cheap option if it works ???
Good luck.
2004 Golf GT TDI 132k