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Discussion Starter #1
Hi I have a T4 with the 2.5 Petol AAF engine that has started running rough when cold. Any ideas?

When starting it from cold, the engine hunts. Try and drive it before it warms up and revs don't want to climb very easily. When you come to a stop at a junction say, and dip the clutch, the revs often die away to nothing and the engine stops. It starts again no problem. Once warm it runs great and pulls like a train. I've not had the van long but it seems like the engine takes a while to warm up anyway.

Though on the last trip I made I was in traffic on the M25 and the engine did stop twice as above but when warm. Started no problem each time. As I said, the engine will only stop when you dip the clutch as you pull up.

The other curious thing is if you stop the engine for 5 or ten minutes (with the engine up to temp), when you return to it, the engine will hunt for 60 seconds or so like when it is cold until the temp gauge climbs back up to normal running temp.

There are no fault codes on the ECU. And I've put a bottle of injector cleaner through it with no success.

Any ideas would be appreciated. Thanks in advance.

Ben
 

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Discussion Starter #3
Thank you, Steve. Will a leaking hose or I guess, manifold only show itself when cold? That being said, it has stalled 3 times now when warm.

Provided I'm looking in the right places they don't look new, that's for sure. That's if I'm looking at all of them. Looks like I might be getting out of my depth. A Haynes manual if I can track one down would have a vacuum diagram I hope.

Ben
 

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Don't think Haynes coveres the petrols. There's lots of info on the vag Erwin site, and is cheaper than a Haynes manual too. If not, pm me tomorrow and I'll take a look, I've got a whole bunch of vw manuals on my laptop.

With Steve on this one, sounds like an air leak. Check the breather elbow that goes into the pipe between the maf and the throttle body.
 

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Discussion Starter #7 (Edited)
Thank you both. Best to check all of these hoses, elbows and unions in the diagram, then to be sure? Which is the elbow you're talking about, d-9? Is it the one next to the clip marked 10? I'm excited to get it fixed. Might not get to it until Monday but I'll let you know how I get on.

Ben
 

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Other things to check are the 2 pin temperature sensor, the idle control valve (ICV) and the the connector at the ICV. The ignition pack can also cause intermittent problems due to damp.
If it's the sensor it normally shows a fault on diagnostics, but not all the time
 

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Discussion Starter #9
Thanks Spanners. I'll go through all these things.

And thanks folks. With your advice I've found previous posts with a similar problem (though on the 2 litre).

I didn't find them before because i didn't know what to look for! So thanks for your patience answering an old question!!

Ben
 

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My one had a similar problem. Garage could not fix it and VW said it was because I used lpg. It turned out to be the small vacuum hose that runs from the head to the ECU.
 

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Discussion Starter #14
Sorry guys, gonna resolve this rather old thread with an update. It's still not right. Hoping to push my luck with you lot!

I found a perished small hose connected either side of the air filter, changed that and all the small hoses between the throttle body, accumulator, MAF and bulkhead. There was an encouraging pffffft sound as I took off the one way valve at the accumulator. That works... The car had been standing a week. But still, no dice.

I also changed the ICV and noticed that the hot stalling in traffic has stopped but otherwise the problem still remains the same. I did find a little oil in the u shaped hose from that to the block. That's normal, right?

I quickly ran out of talent and took it to my favourite VW specialist last week armed with a print out of this thread. He has since checked the ECU has a good vacuum, and has changed 3 temp senders (green, blue and another one) and is happy with the vacuum hoses. The live data on the ECU isn't very sophisticated as I'm sure you know. The LAMDA probe he says is giving a varying voltage (or is it resistance?) when running and seems right but we don't know what range it should be.

Finally, putting the ECU to base values causes it to stall. Winding the idle screw on the throttle body all the way out just kept it running. So the throttle body has been off, cleaned and checked over - still no success. The van won't run on base values.

There can't be a lot left! Change the LAMDA?
 

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A specialist and he does not know what readings you should be getting from the O2 sensor (Lambda sensor) ????
Hmmmmmm

If it is a Zirconia sensor then you should have a varying voltage between 200mv to 800mv switching every second.
If it's the Titania type then voltage reading would be 500mv to 4.5v
 

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Discussion Starter #16
Thank you I'll pass that on. Perhaps I've misunderstood what he was getting at but I'm getting a desperate to get it fixed. It's been rough running longer than its run right since we got it!
 

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What condition it the ECU vacuum "receptor" in. (not the correct term but there is a perishable rubber bag inside the ecu that detects pressure change).
 

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Discussion Starter #19
A common thread running through this, er.....thread is the vacuum pipes. I think replacing them all is the way forward. The ECU 'bag' is a new one thank you.

Ben
 

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Maybe of no help whatsoever but I had a 1.6 VW Polo that did the same stall thing when cold - I used to drive it to work in mornings and it would die when I dipped the clutch to stop at a junction / roundabout, and I'd roll out with no brakes / steering lol. A: Turned out to be sticking / dirty butterfly valve in throttle body, maybe worth checking?
 
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