Very intermittent bucking

[golfgtdude]

Hi all,

My Golf Mk7 GT TDI Bluemotion (150bhp) has been exhibiting this very intermittent bucking whilst driving under light throttle (between 1500-2000rpm). It had also started doing it when moving off from a standstill which is a bit worrying with the fear of the vehicle behind rear ending you.

I've tried many injector cleaners through the tank, new air filters and also two fuel filters and nothing improved it.
I have VCDS and it reports no faults. I even tried monitoring the fuel injectors and from what I can tell they appear to be operating within their tolerances.
The car starts fine, returns excellent fuel economy and pulls like a train on hard throttle to the red line. Mileage is around 82,000. The issue has been there for several thousand miles.

Most recently I considered swapping out the MAF as it was comparably the cheapest option to taking it into a garage to start changing more expensive components in order to troubleshoot. However I decided for the sake of £10 to give cleaning it a go, and tried this Luqui Moly MAF cleaner. I did just that and to my surprise it seemed to have resolve the bucking between 1500-2000 and made it more responsive to drive. However a week later the problem has returned but now showing itself intermittently between 4000-5000rpm.

I know I might be stating the obvious here but could I just have a dodgy MAF sensor here or just is this masking something more serious?

 

[acoustic_]

Are you using an oiled air filter?

I'd say easiest thing would be to swap the MAF. The cleaner "fixing" the issue for a short time points at the MAF, at least. I'd verify the MAF is clean; when you pulled the MAF out was it dirty/oily?

 

[golfgtdude]

Are you using an oiled air filter?

I'd say easiest thing would be to swap the MAF. The cleaner "fixing" the issue for a short time points at the MAF, at least. I'd verify the MAF is clean; when you pulled the MAF out was it dirty/oily?

In the past I ran a Pipercross panel filter for about 20-30k miles then removed it and went back to the standard paper filter.
Difficult to tell if the actual electronic sensor was dirty as you can't get to it but the outer mesh area was sooty. I tried my best to douse it all in cleaner, left it to dry.
I might go for a new MAF next and see if it fixes it.

 

[acoustic_]

You could try cleaning it again, but might need to get in there better. I'd be curious to see if the MAF was "sooty" again, so soon after spraying it with cleaner..

 

[golfgtdude]

Yep but it's too hard to tell on these what it is to clean. I did try spraying from all angles to no avail.
I've ordered a new MAF sensor for now which is 8x the cost of the cleaner.

 

[golfgtdude]

just an update.
MAF cleaned once, improved things will bucking less frequent.
Cleaned the MAF for second time and car no longer exhibits this issue.

 

[golfgtdude]

And another update… as it turned out the MAF didn’t fix it but the actually problem eventually showed itself.

The problem has been odd since it used to only effect low revs but one day decided it would buck at high revs. I figured it may be something serious and considered selling the car.

The engine management light finally came up one day after severe buck and conk out at a junction. I ran my diags on it and it said it was the engine speed sensor (non signal). Cleared the error and persevered with it. The bucking would come and go until recently it conked out again with the a similar error fr the same sensor. Decided after that I would change this sensor as it’s only a £15 part.

I’ve changed the crank shaft sensor which is what the speed sensor relates to and everything is going well now.

It’s a pig to get at and required removal of the oil filter housing, a mirror and good levels of light to did the 4mm allen screw to get it out.

I hope this goes some way to helping others who have similar issues.