Intermittent power 'dip' on motorway

[privatemeekly]

So, when driving my B7 on the motorway at 70, I sometimes notice a feeling that I can only describe like as if there is suddenly more resistance against the car. The speed doesn't drop, and if I have to adjust the accelerator position, I don't notice it. It will then, after a few seconds suddenly feel 'right' again.


VCDS shows no codes, fuel filter is only 40k miles old, air filter under a year. I can't see anything odd under the bonnet, other than an exhaust leak from somewhere in there.


Does anyone have any suggestions please?

[Crasher]

Wipers running?

[privatemeekly]

Oddly enough, I had thought that it only happens when its raining (but guessed I must me imagining it)... Some really odd electronic thing?

[Crasher]

Yes, disc wiping; it keeps the discs clean of water so the brakes respond when needed. It can be turned off but that’s not a great idea.

[privatemeekly]

OK, at first I thought you were taking the mick (sorry) but after a google, it should only happen for 15 wheel revolutions, right? which should be around 1second at 70. This lasts for around 5 seconds or so, could it be this, just having a bit of a moment? Also, I've had this car for around 6 years, and have only noticed it in the last 6-8 months or so. I did at that time have a sticky caliper on the front, which has deffo done something to the disc - as I have a wonderful judder through the steering wheel on when I brake.... (I know, time for new discs and pads!)

[Crasher]

I had a Passat like yours do this and we traced it (eventually) the the rain sensing unit in the mirror of all things. If this never happens in the dry with the wipers off it does point to the ABS pump.

[privatemeekly]

Thanks Crasher.

Sorry it took so long to reply.

What was up with the rain sensing unit? And, anything I can measure with VCDS to see exactly why it is behaving oddly? I'm doing caliper / discs / pads on the front this weekend, as I don't trust the one that was sticky previously. Hopefully this will mean I don't feel it any more (I can always wish eh?)

[Crasher]

Just a hunch and it worked.