Unfixable starting problem. Three mechanics later...

I have a VW Golf tdi manual 1.6 with 215 000km on it. In the last 8 months it has had the timing belt done, a new MAF sensor, new Coolant temp sensor, EGR cleaned out. Always serviced etc.

Apologies for long post - (and I hope it's in the right place!) but this car has a big problem....and three mechanics haven't been able to fix it (including the VW dealership)

First big problem - cold start. About 6 months ago it developed a stumbling idle on cold start (weather was about 20c overnight, so not 'cold'). This has gotten progressively worse. Car starts immediately and idles perfectly for about 1-2 seconds. Then it suddenly develops a very bad stumbling idle. Best way to describe it is it feels like you're in a petrol car when it's firing on one or two cylinders. Throttle is unresponsive throughout. Car stumbles until it stalls - or I turn it off - about 6 seconds of 'running'. Does not matter if you start car with throttle or without - tried all different ways.

Car will start again immediately and do the same thing, but slightly less badly. After about four or five starts it runs, and then revs, and then runs fine. No codes or CEL etc.

Second problem; Cruising with wide open throttle, fifth gear on a slight uphill, then when you go downhill and car is 'coasting' (but still in gear) with no throttle. it throws glowplug CEL and code, which so far has always been p0101. Sometimes the car goes into limp mode, which is really comforting when a huge truck is right up my bum on the highway (heart attack material).

Third problem; sometimes it stumble-farts/lose power for a couple of seconds during normal (engine normal temp) driving. Sometimes it goes into limp mode when this happens. Maybe it is fixed now though....because.....

I bought the car with an Oettinger tune box proffessionally fitted. This has now been removed. Car runs more quietly and smoothly - although was mostly good before. The occasional stumble/fart problem during normal driving appears to be fixed. But CEL still comes on as per conditions above (WOT then coasting). And the cold start problem is the same.

As soon as engine is warm car runs like a dream. I do mostly highway driving and make sure it gets an Italian tune up every time it runs - some full throttle/boost etc. Once started car produces a bit of white smoke, presumably burning off the fuel that's built up during bad starting. That clears quickly then it's fine, nothing visible at all. Turbo feels totally fine - power feels normal, all seems to kick in at the right time.

WHAT HAS BEEN DONE SO FAR;

- Fuel pressure and delivery is apparently fine - this has been checked by mechanic.

- VW dealership mechanic replaced three wires into MAF (apparently was a common VW fault), but no change to vehicle (except $500 poorer). He did clear codes and plug car in to diag.machine - looked normal apparently.

- Car has not had Dieselgate emissions recall software update. There are no outstanding software updates.

BEST GUESSES

- Sticky EGR causing air intake on startup, and also when engine dropping suddenly in revs from about 2000 to idle. But; EGR has been cleaned (but can be useless if there's too much crud in the inlet manifold) and also car starts fine, just won't idle. This would potentially cause MAF code?

- ECU fault that kicks in 1-2 seconds after initial cold start and tells engine to squirt more fuel in. Or maybe something like coolant temp sensor telling lies to ECU....but this is a new sensor?? And no codes showing....Was no different after coolant temp sensor was replaced.

- Injectors......but then shouldn't I expect some other issues when driving? Car starts perfectly and runs perfect until the crazy idle kicks in. Also car is fine as soon as it has been running for about a minute (although I get that everything seals better when it's warm)

- I've read a lot about water in intercooler pipes. Have not checked this but it seems to start completely fine, just crap out almost immediately. Not sure these symptoms suggest for water in intercooler. It's also not cold here (comparatively - never gets below 0c).

Have ordered a VCDS which will arrive in a few days. Will be able to check lots of stuff but injectors are first on list.

Sorry for long post but this car has been to three mechanics - the VW dealer workshop, my local mechanic (who does heaps of diesel) and a Euro cars expert and still no-one can fix it. I feel like I just pay people money and it makes absolutely no difference. No-one can fix this car....

Any advice very, very much appreciated...

Only comment I can make is related to water in intercooler. I’ve had maybe twenty issues in the nearly four years I’ve had the car. Loss of power a few seconds or maybe a minute after starting has been my experience. Usually rough running for a few seconds after starting to move and the engine got up toward 2000 rpm. Happened at all temperatures above freezing, only once when below freezing. I could almost always relate it to longer periods of low power operation followed by slower engine speeds before shutdown.

I drilled a 1/8 hole in the intercooler piping low spot last year and have only had one issue since. The car started, stalled and then a fair sized puddle of quite clean water collected underneath. Maybe the hole had plugged and starting blew it clear?

White smoke doesn’t seem right, unless it coincides with poor running. I wonder if you have a frustrating wiring problem, possibly caused by some previous ‘mechanic’ fixing or playing around under the hood?

A good place to start would be to remove the tuning box, throw it in the trash and restore the stock wiring. "Professionally installing" a tuning box usually means unplugging some plugs on your engine and plugging the tuning box inline with your stock wiring. About on par with "professionally installing" an air freshener or a plug in cell phone charger.

Hopefully, the tuning box didn't do any permanent damage.

"Second problem; Cruising with wide open throttle, fifth gear on a slight uphill, then when you go downhill and car is 'coasting' (but still in gear) with no throttle. it throws glowplug CEL and code, which so far has always been p0101. Sometimes the car goes into limp mode, which is really comforting when a huge truck is right up my bum on the highway (heart attack material)."

Even though I have an older model, I think the cause could be the same. I had the same thing happen with mine.

It turned out to be an EGR valve that was not closing properly, even though I had EGR tuned out. BTW, P0101 is MAF implausible code, not glow plugs. Block off plate solved the problem.

Pretty good bet- It's the injectors

There are several routines inside the ECU that evaluate the individual cylinders on an ongoing basis. This is not unlike the "injector balance" that most are familiar with on the good 'ol ALH, but only in a general sense. Much more complicated. The IVA/IMA values are one component of this that some may be familiar with.

The way the cars are set up from the factory, some components of the injector learning adaptation don't kick in until 50c coolant temperature or so. When it reaches 50C all the adaptations are running so it smooths everything out.

That's why it runs badly when it is cold but runs fantastic when it is warm. The North American "Bin5" cars, (I hesitate to say "clean diesel" lol) there will be a "cylinder x torque deviation" fault in the same situation, which helps figure out which is the errant injector(s). Your car being Euro 4 (most likely) probably does not have fault reporting for the individual cylinder torque contribution, so there is no fault to show, and troubleshooting is not as easy.

WHat you can do: For starters, when the car is warmed up, look at the cylinder injector balance smooth running control which is VCDS measuring blocks group 13 measuring blocks in the USA-market MK6 (not sure of which it is for your car) and there may be some indication of which injector(s) is "off" so to speak.

I would start there.