Rough running VR6

[tony_ack 0]

The car has been running pretty rough lately, and I'm scrathing my head and could do with a fresh perspective - can anyone point me in the right direction as to what might be wrong to save me replacing everything?

• Takes a while to start from cold sometimes - strong crank, turns over and over for about 10 seconds then starts to splutter into life before finally firing up. Other times starts first time
• Popping on overrun once warm - does it nearly every time (quite severe) and even does it sometimes when changing up a gear
• Erratic idle - sometimes okay at about 600-650, sometimes goes up to about 800rpm.
• Cuts out when approaching junctions sometimes (I know, standard VR)
• Idle adaptation exceeded error on Vagcom, when checked the adaptation value is up at more than 1.2
• Flat spot at about 2.5k rpm

It's never been this bad in 10 years of ownership.

 

[_Matt_ 32]

The simpliest place to start is checking for vac leaks. This sort of stuff can cause all of those types of issues, especially flat feeling and cutting out.

Secondly, when were the timing chains last done? Idle adaption seems it's trying to counter something and also sounds like it is overfuelling with the popping but could just be running out of time.

Before i had my chains done my car was hard to start when warm and was flat feeling in the mid range. The idle wasn't smooth - juddered slightly every few second or two at idle. I dind't have an adaption errors though.

Assume no other codes? There is a cam sensor up the top of the engine that can cause running issues.

Any other maintance done over the last 10 years of note to help steer troubleshooting?

Cheers

Matt

[Dox 23]

You can check coolant temp sensor with VCDS?

Check the leads for cross firing (sparks jumping across leads) - in the dark and mist water on them with a hand pump spray.

Cam sensor can give long cranking when faulty.

Don't assume that recently replaced parts can't be faulty, 30 year old VW parts are often more reliable than Chinese replacements....

[Bruno 4]

five common causes of what you have (below). It can be a combination of these: 

1. Spark plug leads
2. Cam position sensor throwing spurious errors.
3. Lambda probe knackered or covered in oil.
4. Leaking valve stems and/or leaking pistons on Cylinders 1 or 6. Get a compression tester test for valve leaks and piston ring blowback. ABVs tend to go through valve stems faster than AAA engines.
5. Fuel pump weak.

Given what you've described, I'd go down the list in the order given above.

[tony_ack 0]

Thanks for all the suggestions. 

I found that the plug lead on 1 was loose last night - I put it back on properly and it improved for a bit then started doing it again. I took it off again and noticed quite a bit of corrosion inside. I've cleaned it up with a file and contact cleaner, and now it idles bang on 650 when warm, popping had gone (has just started again a little after about 10 miles), and power is smooth.

I think the fact it cleared up after messing with the plug lead suggests I've found the issue - I just need to get some new leads now.

Thanks again for all the help!

[_Matt_ 32]

Good it was somehting so simple! I remember now Vince telling me to check sparks and leads when I had bit of rough running as first port of call now you mention it.