VR6 stutters and runs a little rich

[iep]

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?

Cheers,

Ivan

[iep]

Bit of reseach suggests the MAF might be at fault. Anyone have any thoughts on this?

As an aside, has anyone got any thoughts on the quality of MAF that you can get from GSF?

Cheers.

[Crasher]

Have you done a fault code read? 95 VR6 AMM's (021 906 462 @ £221.49 from VAG) are very reliable but when I need them, the aftermarket ones are very tempting due to the high genuine price. In the few instances I have used aftermarket supplied VR6 AMM's, they have been fine.

[iep]

Thanks crasher, that's good to hear. Ordered one today. I've done a fault code readout and logged lambda readings on a short drive today and found no issues (lambda output cycled nicely around 1 and no engine fault codes reported). Essentially, I'm going with the MAF theory because I've tried nearly everything else I can think of and had no joy. Part should arrive on Monday so I'll update then.

Only other thing I have heard of that might cause this is a vacuum leak on the air intake manifold (can't find one) or a clogged crankcase breather (not sure how/why this would cause hesitation under acceleration). Ever heard of this? Do you know where the crankcase breather is routed?

Cheers,

Ivan

[Crasher]

The breather is in the cam cover, they don't get blocked on the VR6. The fouled plug worries me, was it number 6?

[iep]

In fact, all plugs were a little black. Not totally coked up or oily, just dusted with black rather than brown deposits. Since the engine runs well (no smoke, no oil or coolant loss) I don't believe that this is a head or gasket issue but I'll try to find time to do a quick comp/leak down test over the next couple of weeks to be sure.

I thought there was a second breather attached to a charcoal filter that is clipped onto the airbox itself (from Russek manual)?

[Crasher]

Ahh, the tank vent valve, not the engine breather. Yes, they can stick open but should give a code. Clamp the hose to see if it helps.

[iep]

Nice, so that it what it is. Couldn't puzzle it out at all.

So the pipe coming from the top of the cam cover (drivers side) is the only breather? In that case, it is fine. clamping tank breather hose made no difference so I'll try out the MAF on monday and see how that goes.

Meantime, waxed the car instead. At least it looks faster.

[Crasher]

Yes the breather from the cam cover is the only crankcase breather.

[iep]

Well, that's feckin dissapointing. Fitted MAF this evening , took it for a drive and problem still persists. Stick into fifth gear at 1000rpm and put my foot down. Car starts to accelerate normally and then at 1200rpm starts to judders violently until it hits 1500rpm. Gutted.

Definitely only happens as low revs, warm engine (90deg) and seems to occur equally often when weather is wet or dry.

So far:

new plugs
new coil pack
new MAF
cleaned ISV
checked air filter (okay)

Not much left that I can think of unless the ECU is on its way out. Seems odd that it would only fail under these specific conditions though.

On the upside, I have a perfectly functional VR6 MAF for sale if anyone is interested? Does anyone have any other ideas of things I could check? This small prolem is really spoiling the car.

Cheers.