Surging during engine braking

Recently my car has begun occasionally surging while "engine braking" ie while coasting in gear (clutch engaged, no brake or accelerator pedal applied). The car gradually slows as it should and then will surge as if I had stepped on the accelerator pedal but without me touching it. It is a bit disconcerting and has been occurring with increased frequency.

Any ideas what may be going on?

Not sure if it is related but I have for the first time had the car go into limp mode recently on longer up hill drives and am having some VSS issues I think on the front driver's side wheel that set off the ABS and ESP lights.

I do have VCDS if there is a scan or module to track that someone can suggest.

Thanks!

This happens above idling speed?

Yes it happens above idling engine speed.

Might be some restriction in the air intake system. Since the turbo is not producing pressure, the air system is producing vacuum, could an intake hose be collapsing?

zzdiesel said:

Might be some restriction in the air intake system. Since the turbo is not producing pressure, the air system is producing vacuum, could an intake hose be collapsing?

Click to expand...

If that's the case it may explain my occasional limp mode too. I will look into it.

I am reviving this thread from the dead because this issue is still happening and is increasingly happening. Coasting down a long hill in gear the car will (usually but not always) surge for a split second several times over a 20 second coast. It is important to note that there is no surging while accelerating or idling. The rpms do seem to "hang" after a hard acceleration sometimes.

Other issues that are occurring these days:

Occasional limp mode on steep inclines. I can get rid of this for a while by doing an "Italian tune-up" ie driving it very hard to high rpms

and

Lots of smoke on cold starts. Whitish-blue smoke. No loss of coolant or oil though.

I see no sign of a collapsed intake hose. I have recently replaced the air filter. I am thinking of removing the intake and cleaning it and maybe replacing the injector wiring harness. I have the EGR deleted recently but have never cleaned the intake (this engine had an EGR with no cooler).

Any ideas?

QuickTD, thanks for the idea. As far as I know there is no clutch switch wired in. No lock preventing starting without the clutch pedal pressed. It has been this way since the swap years ago though and this surging only started a year or so ago. I will keep it in mind though. Never figured out how to wire it in yet.

I see. I didn't know they were separate switches. My revs definitely hang more than on most cars (like my Jetta). This car was swapped auto to manual as well as the engine swap. I don't know for sure whether or not the clutch switch was connected (no cruise btw). No tune required I imagine for the auto to manual swap as the ecu was also swapped in with the engine and manual tranny.

I will check with VCDS.

It looks like QuickTD was right! I installed the clutch switch and no more surging!... for a while at least.

I installed the clutch switch as shown in the video in this thread: http://forums.tdiclub.com/showthread.php?t=468731

I did not need to change the pin number on the ECU wiring as my ECU is from a manual tranny car. For the first little while the revs didn't hang and no more surging while engine braking. Then I got the flashing glow plug light and realized I had not plugged the brake switch harness back in fully. When I did the clutch switch stopped working!

I have tested the current in the wiring and all appears correct - 12v power flowing through the clutch switch when the clutch is not depressed and no power flowing through when it is depressed.

I have tested it and the clutch switch will only work (ie no rev hanging and no surging) ONLY when the brake switch is unplugged. This makes no sense to me. Anyone have any ideas?

I am fairly certain my problem getting the clutch switch to work is the wrong ecu pin#. Anyone able to look up what ecu pin# the clutch switch is supposed to go in on a 2003 AVF engine ecu?

It would be much appreciated!

Thanks QuickTD for the Pin#! Thanks also to Jamie in Salmon Arm for helping me repin the wire. I now have a working clutch switch!

No more rev hang. It 'seems' to have almost 100% solved the surging issue too but I have still noticed a couple of little surges here and there still.

One other mysterious thing that has occurred is that the car now idles around 900rpm whereas before it idled at 830rpm. We did change the engine coding from manual fwd to manual awd. I wonder if this messed with the Malone tune I had changing the idle speed? Not sure why the tune would have me idling at 830rpm though....

Interesting... I will look into whether or not I can change the idle speed. I like the higher idle, a lot less rattling in the car. In particular the exhaust used to rattle a bit at idle.

It seems like the surging has returned. Very strange. It really did go away for about 200kms of driving. I am stumped. Still happy to have the clutch switch working though!

Yup, the surging is back unfortunately. Totally stumped!

I did check with VCDS and I can alter the idle speed in channel 2 of engine adaptation. Very cool! Turns out my Malone tune only works in the fwd engine coding and not any of the other options. Bummer. Can't see any other effects of changing the coding though so no big deal right now...