Occasional rough idle/stall on cold start - camshaft sensor?

[negev]

I have a 2005 B5.5 passat with the 130 PD engine.

If the car is cold and I start it and immediately drive a very short distance (i.e. pulling out into a queue of traffic), then put the clutch it, it will often start hunting (rev needle going down and hearing a bag every couple of seconds) and sometimes it will even stall. When it stalls, on restart it runs fine with no more issues.

If I let it warm up for a minute before driving it's fine. If it starts hunting and I hold it above 1000rpm for a few seconds then it's also fine. Once it's been running for a few minutes it runs fine and never skips a beat.

What could be causing this? I can't believe it's a vacuum leak because it would be more consistently problematic, same for a general timing issue. Could it be an ageing injection pump or possibly a camshaft sensor going bad without throwing a code?

[smithy602179]

Try removing the vacuum pipe to the egr and plug the vacuum pipe and try it . I had similar problem and left egr disconnected

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[negev]

Try removing the vacuum pipe to the egr and plug the vacuum pipe and try it . I had similar problem and left egr disconnected

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My EGR was replaced fairly recently, including the thing pipe that runs to it, so I don't think it's going to be the EGR.

[smithy602179]

My egr was new too but I found mine would stall too till I disconnected the pipe . It don't cost owt to try

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[negev]

Fair point, where is the pipe? Do I need to removing anything to get to it? Sorry I'm a total noob with anything under the bonnet..

[smithy602179]

Pipe is on top of engine left side as u look at engine. round silver thing pull pipe off and put a bolt in the end of the rubber pipe .

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[Rob69]

With that age engine it could be injector wiring harness, MAF sensor, tandem pump or air in fuel, clearing the air after a few mins running. A scan would be good starting point and thorough check of all fuel and vacuum hoses, could be egr related but i tend to think air getting in fuel or in tank fuel pump not supplying the tandem pump and tandem pump being starved on start up after the engine has stood for a while.

[negev]

With that age engine it could be injector wiring harness, MAF sensor, tandem pump or air in fuel, clearing the air after a few mins running. A scan would be good starting point and thorough check of all fuel and vacuum hoses, could be egr related but i tend to think air getting in fuel or in tank fuel pump not supplying the tandem pump and tandem pump being starved on start up after the engine has stood for a while.

Thanks, is the tandem pump the same as the vacuum pump? If so it was replaced recently so should be good. I've had this issue for months, scanned it many times but no codes. So possibly loom, maf or fuel pump.. is there a way to narrow it down without spending lots of money on guesses?

Also odd is that it seems to be worse if I've got the steering on full lock when the clutch goes in, I guess because the pump is working sapping power from the engine? When it runs rough its like a cycle, bangs every couple of seconds like the timing is thrown out.

If I just work around it will the occasional bang cause any damage? I guess its probably a misfire but I thought a misfire would throw codes and a CEL.

[smithy602179]

Wat was the solution to all your woes

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[negev]

Wat was the solution to all your woes

I took it in recently and the first thing they found was that the top pipe had snapped off the EGR valve (!!). It was only replaced a couple of months ago so I took it back to where it was fitted and they replaced it under warranty. Issue still persists though so now it's booked in again for Monday.