VR6 stutters and runs a little rich

[ip 0]

Hi, so I've had my 1995 Golf VR6 for about 3 months now and am largely pleased with it. Bought it quite cheap so don't mind having done the following on it so far:

Radiator (holed)

Thermostat, temp sense and sender (engine was running cold)

Ignition switch (wouldn't start consistently)

Plugs and Coil Pack (trying to solve stuttering issue)

No ECU falut codes reported since changing temp sensor/sender

So, more on this stuttering. Car runs great above 2000rpm, never any issues. Between 600 and 2000 though, if you try to accelerate, the engine will sometimes briefly stutter and then pick up again. Sometines it will do this several times very quickly (3 or four in a second or so) but always settles out. Hugely annoying to drive.

When changing the plugs to see if this would help (it did not), I noted that the old set were a little coked up and not the matt brown that my last VW produced. I'm confident that this is not to do with the engine running cold issue that I solved by changing the thermostat becuse I did this over 2 months back (and so would expect the deposits to have burned off by now if the engine was now running correctly).

Idle is smooth once warm and MPG is about 25 round town so not too low (I get 31MPG on the motorway which is a little lower than some report but I do tend to boot it where I can). When cold, the revs will wander a little at idle but only by 100rpm or so and only for the first minute or so that the engine is running. It hasn't used a drop of oil in the 3 months since I bought it and no sign of coolant leakage since I fixed the radiator

Does anyone have any thoughts at all about what might be causing the stuttering performance and/or running rich?

[Devildub_06 0]

Does it only stutter when warm? The wandering idle when cold may well be the idle air bypass valve which is getting a bit gunked up (clean it out and see if it makes a difference).

I'd also start by making sure the air filter was clean and that the MAF is clean too.

[sticks 0]

hi devildub any chance of telling me where the idle air bypass valve is or a pic,as sounds abit like mine in the morning,also get a whistle in the morning like a trumpet noise when slowng down only in the morning tho,

cheers

[Devildub_06 0]

Hi sticks, can't wing a picture at the mo, but the easiest way to find the unit (Not sure if it's exactly the same for OBD1 and OBD2 cars), if you follow the tubing back from the air filter, past the Mass Air Flow sensor, you will notice a pipe that comes out just before the throttle butterfly and goes into a small unit that will have an electrical plug on it also, this will then have a pipe coming off the other side of it that reconnects after the throttle butterfly. This is the offending idle bypass, and hope this helps and/or I can be corrected for different types.

[ip 0]

Hi, thanks for all comments. Sorry for slow response. Been away from PC for a couple of days.

Right, quick update. Idle when cold, not particularly bad only first 5 secs or so (soars highand then dies down). Might be normal, just seems higher than my last VW. Saying that, removed and cleaned ISV (bypass valve). No great change.

Replaced MAF this week and made no difference. Gutted since it cost £188 from the dealer. On the upside though, I have a perfectly good VR6 MAF for sale if anyone needs one?

I also checked the throttle pot today (fine) and fuel pressure (fine).

Since I've already done the coil pack and plugs, I'm left with only the HT leads to change so will give them a shot next. Fortunately, my mate has a spare set so I can try before I buy.

Does anyone have any other thoughts?

Cheers

ip

[Devildub_06 0]

Have it VAGcom'd to see if it brings up lambda or crank sensor issues. Someone else recently had a similar prob and it turned out to be a broken lambda wire.

[Dave Lea 4]

have u scand ecu might shed sum light on it pos crank or cam sensor fault

[ip 0]

scanned it several times over last two weeks (to see if any faults were appearing then self clearing). No reported issues from ECU at all.

[Devildub_06 0]

If you have done all that work, I would start looking lambda sensor region, may be corrected here again but a scan may not necessarily bring up a lambda probe fault (Not exactly sure when the OBD1/2 changeover year is, but OBD1 is a lot less informative on error recall). I would just check the wiring and plug, even whip out the probe itself if convenient to make sure it's not excessively coked up.

[ip 0]

Fair comment. It is running a little rich so this could point to a lambda probe issue. Saying that, I took a log of the lambda output on a recent test drive and didn't notice anything to untoward. All values within the 0.9 to 1.1 range and no abrupt changes in mean value.

[Dave Lea 4]

had a crank sensor on a 94 vr last year no coed and running ritch and stutering replaced it and all was ok but as every thing this may not b your falt but many things can make that happen we are all guessing here

[ip 0]

Wow, I haven't heard of that before. Is the crank sensor the G28 engine speed sensor found beneath the oil cooler? Also , how did you figure it out to even try that? Any other symtoms? Thanks.

[Dave Lea 4]

had a donor car we was just trying stuff and that fixed it same prob as you

[ip 0]

Just to be sure, are we talking about the sensor below the oil cooler (referred to as the engine speed sensor (G28) in vag_com)?

[Dave Lea 4]

yes but i did change the cam sensor as well before and ran it it was still the same so both might of been faulty i left both in though

[ip 0]

Well, after all that new HT leads (borrowed from a mate) cleared problem right up! Only thing I hadn't changed. Runs sweet now and pulls smoothly from 680rpm all the way up.

Thanks again for all the advice. I guess I've learned two things.

1, The simplest explanation is the one to start with.

2. VR6s are very fussy about HT leads.

Meantime, I've spent a bit on plugs and a coil pack but they needed changing anyway so no harm done. Only annoyance is changing the MAF for no reason. Hopefuly I can shift the old one on ebay.

Cheers,

ip.

[cav 0]

i also had a search idle rate and running rich..

replaced the lambda sensor and coolant temp switch.. all is well

[cav 0]

and now not well again...

can not figure this one out now and starting to get to me.

lambda and coolant temp switch changed along with thermostat, water pump.

The engine now idles at 1.5k and dips every so often as though it needs to drop (ecu trying etc). Its over fuelling.. probably to the ecu's 25% safe mode. before it had an idle of 1.5k, it idled ok.. but the first 500revs after that, it would be very spluttery, you can get the induction to pop easily -- hence why i say its over fuelling. after that its ok... but when accelerating it would bog down.

Searching idle is still there but not as bad.

I also have no rad fan or elec water pump, so i need to get a fan controller.

If it were the crank sensor or cam sensor out.. what would it do? whats its purpose etc.. as i am tempted to get those next.

any help would be appreciated.

Cav