Car surging problem

**sierra055** · 07-04-2010, 09:51 PM

Hi everyone...
I've been having a frustrating issue with my MK4 for a little while now where the car seems to randomly get surging. The car has been great for probably the last 2 years or so, but in the last couple of months the car will surge while driving.
It happens at all different speed and rev ranges and under load or even while cruising at freeway speed.
I've run VAG-COM over it and had a coolant sensor code about a month ago, cleared it, drove 400k's that weekend and 300k a week since and it still hasn't come back (no codes at all now).
I had the car serviced today by Volkspower and asked them to look into it. They checked boost, vac and intake hoses, intercooler and everything is apparently fine.

Car has had ECU upgrade, new SMIC, silicon TIP and typical exhaust work and has driven fine for the last 2 years since all that was done. No other mods or changes have been made since the issue started.

Anyone have any ideas?!

**Merlin8r** · 08-04-2010, 06:52 PM

I'm a total n00b when it comes to dubs, but my first reaction to this is your diverter valve might be cactus. I believe it's a common fault after having a chip installed. I have a new Bailey model on the way, and I haven't chipped yet!

**noone** · 08-04-2010, 07:04 PM

Could be faulty N75 Valve or MAF sensor. Could be a lot of things really...

If you have Vag-com, there are plenty of blocks you can read to try and narrow down the issue

**sierra055** · 09-04-2010, 04:18 PM

Thanks for the replies guys...
N75 valve was only changed a little while ago, and we swapped another on there on Tuesday to test that. DV valve is an APR R1 and definitely no issues there as it happens even when cruising off boost.

I've checked the MAF values through VAG-COM and that seems to be OK with figures of around 120-140g/sec airflow if I recall (spreadsheet is on notebook).
If you have any suggestions as to which blocks to check, i'd be very appreciative