Sluggish Cold Starts

[pudding]

I may have stumbled onto something today.    I've noticed since the Revo 2+ tune (with Revo intake) my long term part throttle trims were +8%.  It shouldn't be that high with software tailored to the intake, and especially not after only 3 days of running the tune.....and even more especially not when running B9, T5, F7.  That's a pretty rich AFR request.

So anyway, out of curiosity, I shoved an old MAF in (it's about 3 years old) on my lunch break and since then it's driven a lot better.  Smoother, quieter, more responsive.  All of it.
I will see if stone cold startups improve also.

The previous MAF was bought this summer from VW.  It was covered in engine oil when I took it out to pop into the Revo intake, which I can only guess came from excessive turbo surge.  There is no oil in the dump valve pipe work.   Since the MAF is very close to the rear PCV and the turbo, excessive turbulence down there will back flow oily air onto the MAF.   I guess it's f'cked then.   Sensitive little things.  I will see if I can get VW to swap it out for a new one since their parts have a 2 year warranty.

That was a long winded way of saying - iffy cold starts could be caused by a dodgy MAF.    MAFs are funny things.   They can show no apparent problems, small trims, no fault codes.....and yet.....stick a new/old one and the engine completely changes for the better.   Stupid things.  I always preferred engines that use MAP as load instead of flakey MAFs.

Interesting idea. Is it perhaps worth me unplugging my MAF when I'm home tonight and see how the car starts in the morning with it disconnected?

It's worth a shot.  The MAF gets power during cranking so the ECU must therefore read it for starting up.   Mine started up instantly and settled to smooth idle immediately this morning with the different MAF. It was -1 C at the time.  Best cold start in months!  Too early to say if it's a definitive fix (for mine at least) but it's certainly encouraging!  The slower than usual and lumpy cold idle has gone as well.  Cold throttle response much improved also.

[f00glee]

MAF unplugged - not really holding out any hope, but we shall see tomorrow!

[f00glee]

The MAF being unplugged didn't make any difference. It was a fairly clean start today, but no better than I can achieve if I time it just right. i.e. still a little hesitant and not perfect.

My ED30 occasionally struggled to start, and had to be cranked for a good few seconds. Although the cranking would go weak after a couple of seconds it would always start. I checked my battery voltage, which was healthy. I suspected possibly the starter motor/bad connection. However I cleaned my intake valves (just a job I was planning on doing anyway) recently and have not had any hesitations in starting since this has been done. Our cars have a major issue with this buildup. My runner flaps, and valve ports were coated in about 2-3mm of gunk (2-3mm either side of the runner flaps so they were over double their normal size!) which I can now see would cause problems with starting. My car had only done 73k and the buildup on the valves was ridiculous.

Its interesting you've seen a positive difference in your starts as a result of this. Even though my car is a low miler, it is still 10 years old and therefore may have been subjected to shorter average journeys. I understand this adds to the rate of buildup? I think ill plan to have this done and injectors cleaned at RTech or similar. Probably treat my car for its 40(k) birthday!

[pudding]

40K, wow!  Envious 

Did the engine perform any better with the MAF disconnected?  Normally if the ECU isn't happy with the MAF signal, it substitutes values from other sensors and it often drives better as a result.  If there is no change, the MAF is OK.

I believe the MAF kicks in the moment it fires up.   With my duff MAF, when it caught there was a momentary dip in revs and it was at that point it would either immediately cut out, or stumble and cough for a second or two like a lawnmower engine starting up.   Since the good MAF, starting has been very consistent.  Anyway, I think your issue lies elsewhere.

Cleaning the valves did nothing noticeable on mine, but then again, at 115 odd K they weren't actually carboned up that bad compared to some.  If the build up is bad enough to the point of restricting airflow at startup (there are no compensations other than water/air temp & battery voltage) the ECU doesn't know about it and won't add/subtract fuel accordingly.  Could be worth getting yours checked out!

[f00glee]

I didn't drive with the MAF unplugged - but have done previously with no difference felt. Though at the time I was diagnosing a power issue which in the end turned out to be clogged main catalytic converter.

I've come to realise how lucky I was to find a low-miler. And I plan to keep it for the forseeable, so figure jobs like the inlet clean though maybe not necessary right away (but then again, could be) are something I'd end up doing further down the line anyway. I may as well do it now and know its all squeaky clean, hen ill be enjoying any benefits straight away, not in a few years time. Plus the potential for a leaky injector theorised earlier in this thread will be checked out simultaneously. If I feel like really going for it, Ill throw in some new plugs and coils, too.

Ill likely roll all this into my yearly service, usually march-time, and bring it all forward to maybe Feb. In which case ill report back with any improvements. 

[pudding]

Keep us posted!

In the meantime, you could try a couple of old school methods to help start the engine better? 

[f00glee]

Where do I find the starter handle? If it's meant to be in the spare wheel toolkit, I think i may have lost mine... 

[f00glee]

Inlet/injector clean & service booked in at RTech for Feb. Oil/Filter and potentially plugs/coils/cam follower(current one is on 10k by then, too soon even though mapped now?) at the same time. This will mean in the first two years of ownership pretty much all common points of failure or issue will have been addressed either preventatively or as a necessity. I'm really hoping this good seeing to will yield some benefits, not only in the starting but for the general health of the car going forward. At very least its piece of mind.

As another plus, there's a particularly good stretch of road, The B645 from Saint Neots to Higham Ferrers, which is en route. Any excuse to head towards the midlands from Cambridge via this route!

Ill be sure to report back when done!

[pudding]

It certainly can't hurt to do all that.  Due diligence on the maintenance is the difference between a long lasting GTI and one that suffers from clogged bowels and running problems 

My Nan lives in St Neots. Pretty sure I have been on the B645.  If it's the road I think it is, then I had a lot of fun on that in my old Corrado VR6 Turbo 

[Neil 54]

Hi Pudding are you still getting good cold starts with new MAF as i am still suffering with the same issue

[pudding]

Yeah it's been spot on mate 

[Neil 54]

Thanks Pudding as car is with specialist for another problem i shall ask them to log MAF on start up to see if there is an issue with it

[f00glee]

Had my inlet and injector service at RTech last Friday. This has well and truly solved my cold start splutters. Having made 6 or 8 cold starts since then the car starts very cleanly now indeed. The idle seems smoother and drive-ability is slightly improved through every gear.

I was a little pessimistic about the potential gains but have to say I'm happy to have had it done. Pics of my inlets (red GTI) are on RTechs facebook page - posted 16/02/18 if anyone fancies a look. Even though my car is only at 38k, there was a fair amount of crud in there. Seems the first owners' short trips (suggested by mileage) in the first 9 years may have contributed. Marcus at RTech said he's seen higher mileage cars be cleaner so it seems fair to say that carbon deposits are more related to usage type than mileage. Maybe oil and fuel type too?

Also the injector's peak flow was down 5-7% due to carbon deposits and after a good clean came up to spec nicely.

All of this adds up to a fresher feel especially on that first start of the day.  I'd say if you're experiencing spluttery starts it could be worth considering this service. No obvious immediate gains in terms of power or MPG, the engine does seem generally keener and more responsive, though.

Full disclosure - I did have a new set of plugs at the same time. Though the ones which came out didn't seem bad at all - opted to swap 20k OEMs for a new set of NGKs.

@19TW80  thought you may want to see what I had to say about this. p.s. nice meeting you Friday, the smile on your face after testing your stage 1 eddy said it all. Enjoy!

[pudding]

Interesting!  More likely injector related than the carbon build up, or maybe the new plugs.  Glad it's sorted 

[ROH ECHT]

Here to join the club. Lately, past few months, mine has failed to run on the first start attempt.
I have a seat_key in ignition_shut the door and buckle up_turn the key_let go of the key thinking it can take over on its own_and nothing. Turn the key again and it starts right up.

It's not cold here.
All fueling bits were replaced last summer; LPFP_HPFP_6.6bar Filter_pressure sensors_bamboo fitting opened to 5mm_S3/Golf R injectors.
Inlet valves were cleaned last summer as well and just 1600 miles have been added since.

I have yet to watch any data for pressure prior to starting but this will be done soon.
I have new BKR7EIX plugs and the new APR coils on the way...so waiting for them to arrive and to install those next.
I have the best MAF installed...in that it is newest of the three I have, and reads the highest mass air in the data logs. But I will attempt a start-up with it unplugged soon.
My LTFT is just under +8%...as it has been for a long time. My STFT never points to any leaks when tested following a fault clear.

I will follow up and share anything I have to add. Will take me some time though...as I have become lazy, less motivated to be honest, in dealing with the issues of late. For having to replace all the fueling bits last year and the K04 this year.

It has a fuel like odor coming from the exhaust currently, which I thought may be from the smoke I saw prior to replacing the turbo. But the odor remains and every VW tech and exhaust shop tech I ask now says 'fuel' is the odor. Thinking one or more of the new Golf R injectors installed last summer have an issue, but have been advised to give it some time after having just installed a cat to my catless DP. So the injectors may need to be removed and tested or replaced. Giving it some time because again, last week I went from Catless back to catted DP and the odor seems to be decreasing.