Misfire on part throttle/when cold - also unplugged vacuum hose

[Mk1Matt 0]

I hope someone can help. The car runs really badly for the first few minutes after a cold start. It's got a pretty bad misfire. When warm, it still misfires a little bit under part throttle. It's worse when revving the car in neutral.

I vag-com'd it and it came up with a coolant temp sensor fault but when cleared it didn't come back. I'll check it again this evening and see if it's back now.

I've also found this hose (pictured below). It looks like it once went to the airbox (induction kit now fitted) - can someone confirm? I put my finger over the end to block it this morning but it made no difference to the lumpy idle.

Any thoughts? Are there any tests I can do to narrow down the problem?

Thanks,

Matt

[VR6Nat 9]

that wont cause it, mine has been like that for a year... you can replace it from vw for about 20 odd quid... your misfire could be due to a few things, best thing to start with is the plugs, leads and the coilpack (if yours is a coilpack model) Check for cracks etc... if not try unplugging the maf and see how it runs without that on... then let us know how you get on...

[The Monk 50]

That rubber vac hose slides onto a small nipple that sits on the airbox side just on or behind the throttle body. The throttle body is the small cube that sits on the start of the Inlet mani just after the plastic intake pipe. That can cause an ever so slight lumpy idle, but nothing really noticable.

I've currently got the same issue as you with cold start lumpy idle.

How old are the HT leads and what sort?

As Nat says, try unplugging the Maf. Check the coilpack for cracks too.

[RAPgolfvr6182 2]

id say its the maf mines the same with the induction kit on when cold if i cane it from cold it idle/ run misfires n thats the maf unit at fault

[Mk1Matt 0]

Thanks for the replies. I've noticed the MAF wires have a load of insulation tape around the them. Never a good sign! I'll take a look and try unplugging the MAF to see what it does.

I've used Vagcom to log MAF output on my wife's Galaxy TDI, but can't seem to find the correct measuring block on mine. Maybe it's because it's OBD1 I guess.

The joys of working full time means I won't be able to check it out until the weekend, but at least I'll go in prepared!

Monk - I initially thought HT leads but they look almost new. I'll have a decent nose around the coilpack for cracks.

Cheers all. Can't wait to get to the bottom of this and have it all lovely!

[Scott 0]

+1 on the maf. ive got 2, and one makes the engine idle lumpy, but gets great mpg. The other is down on mpg, but no lumpy idle!

Im wearing the lumpy one just now lol...£1.20 a litre!

[Mk1Matt 0]

An update - I blocked off the unplugged hose and the misfire got a lot better, but it's definitely still there. I've refitted the airbox but couldn't see where the other end of that hose should go. I'm worried that there's still something disconnected somewhere. It's tee'd off from the hose running to the carbon canister.

I tried disconnecting the MAF and running it, and the misfire was still there. I don't want to buy a MAF unless I really need to!

I've heard reports that the ISV causes problems on these when they're cold. Could this be the problem? When it's warm, it's absolutely brilliant.

Coilpack appears crack free. My understanding is that problems with the ignition system are usually only apparent under load, which isn't my problem.

Any more thoughts people?

Ta.

Matt

[Mk1Matt 0]

Further info - from reading another thread it looks like the hose should have gone to some kind of valve in the rocker cover breather hose. Mine has no valve so it looks like it's been replaced in the past. Should the valve be there?

It's the one in this thread: http://www.vr6oc.com/e107_plugins/forum/forum_viewtopic.php?337457