Lumpy idle, backfiring, very hard on fuel... HELP!!

[niall.lambe]

Hi all,

Right yesterday morning my 2006 Golf GTI started backfiring on the way to work, which I liked  but when I stopped at the next roundabout I noticed that the car wouldn't idle properly. it normally sits around 800rpm, but it started bouncing from 800-850rpm. the air stinks of fuel. no EML light on.

The car is a bog standard 50k mile car. only mod is a 3" stainless downpipe and sports cat (fitted approx. 6 months ago). I had it serviced at late november, all filters plugs and fresh oil. Had its annual service with MOT 2 weeks ago.

Left it to my local garage today to check for split boost pipes or vacuum and just got the call to say that all piping is fine. On his diagnostics machine it is showing up as loss of pressure between turbo and Throttle body. thankfully as he couldn't pin point what had failed he wouldn't start replacing parts. Fair play, honest bloke  He has suggested I bring it to VW.

Now looking at previous posts on here it can be one of 2x things, the DV or the PCV. I done the oil cap test a while back, and thankfully the engine started to get rough idle when I opened it. all returned to normal when I tightened up the oil cap again.

Yesterday evening I started the car and it had a rough idle, I disconnected the MAF sensor... no change, still rough idle. I opened up the oil cap... no change still rough idle.

Anyone got any ideas to point me in the right direction?

Cheers,

Niall

[john87]

could be to do with coil packs, but I'd still try and get it hooked up to VCDS or another diagnostic system, as there might still be error codes stored even though the EML hasn't came on.

[niall.lambe]

Just a quick update,

I had the car booked into a specialist for next Wednesday... kind of need the car sooner than then so I done some more hunting on the internet last night of some possible symptoms and fixes due to idling problems.

Done some reading up on what the PCV does. The link I found that I thought was very helpful was:
http://www.mkv-gti.net/wiki/index.php/PCV_valve_failure

"The PCV valve (Positive Crankcase Ventilation valve) is a one-way air valve that allows the flow of "blow-by" gases and vapour to escape into the intake tract upstream of the MAF to be burned with the air/fuel mixture in the combustion chamber". Could this explain why my car was running so lean?? I read on...

"Symptoms of excessive blow-by including oil being pushed up into the air filter, out the dipstick, or out the PCV valve and into the intake manifold where they could solidify on the intake ports and cause the valves to improperly seal over time." In my case the oil has been seeping out the oil cap and down the back of the head.

 "The valve closes/recirculates the gases when boost is present. The positive pressure from boost actually closes the valve." Right so my car only has rough idle, boost seems fine. Hmmm, maybe I will have a look at the PCV Valve then...

So there should be resistance one way and free flowing the other way. So I took the PCV off using a t25 torx screwdriver and gave it a quick clean with a rag and tried blowing/ sucking through it. On my PCV, it was free flowing both ways. I had a look underneath and mine looks to be the original unit fitted to my 2006 GTi as it is dated 12/05, revision D going by the code.

New part required then so. I phoned up Alan Days VW and they had a revised part in stock, revision R they recommended. So I popped round to them to pick it up, got a new gasket to seal it up nice. All off, tested and back on within the hour and the cars running sweet again   

[btowery]

I agree. Likely to be coil packs. Tracking my car, I've burned through a bunch of them. Now using the Audi R8 packs. Don't really know that they're superior, but approximately the same cost and it seems I'm getting longer life with them.

[Dan_FR]

Already resolved and was the PCV. Coilk packs generally start to show their failures under load rather than at idle