Hi all, Not been about on here for many years (kids/house moves etc.) however I'm back with the same MK2 I've owned since I was 18. When it was briefly on the road a few years ago for a house move I was having issues with excessive white smoke and rough running, particularly at idle and funnily enough it's not fixed itself when parked up. This same setup has been running and working well as a daily driver for a few years, the problem just appeared whilst parked up. So I'm confident it's nothing fundamentally wrong. I'm 99% sure it's over fuelling, smells rich, plugs were black and the coolant and oil are all keeping level and clean. I've been trying to get to the bottom of this for a few weeks now with no luck so calling for help! The picture attached is cold idle, it gets 5x worse when warm leaving a cloud behind you. I've tried (and swapped back, apart from the crank position sensor as I've no wish to go through that again) cleaned plugs (newish 3 prong FEBI gapped to 1mm) replaced coil new distributor arm and cap running with lambda/distributor/knock/intake air temp sensors unplugged in turn checked all vac lines throttle body (both position sensor and idle switch) checked white water temp sensor - tested the same as the figures found here; https://www.clubgti.com/forums/inde...p-sensor-testing-possible-overheating.275019/ crank position sensor replaced tried another ECU but ran really rough tried another ISV I did get a timing light on it and it looks to me like there is a 'miss' in the spark where it drops for a revolution, this is most apparent at idle and seems to happen on all cylinders. I am going to go out later once it gets dark and see if there is any stray sparks around the HT system, the leads are in good condition so I would be surprised if there was. I also have an ECU relay 30 on the way to try, but other than that I'm completely stumped. Any suggestions gratefully recieved
Hi guys, anybody got any suggestions for something I've missed? I'm pulling my hair out here Only other thing I can think is fuel pressure, could that be possible?
Hi there, How old is the fuel filter and indeed the fuel your using? - having it sitting idle for a while can gum up the fuel, which can then make its way to filter and generally cause it to behave like a proper bast*rd - ask me how I know. I would also recommend getting new plugs - cleaning/gapping plugs has never worked for me, others may have better results but I definitely didn't. Check all vacuum lines also as they can deteriorate with time. Hope this helps.
Take it for a compression and leak down test. That way you’ll know whether it could be rings or valves.
get the fuel pressure checked, also no ones mentioned the injectors themselves , may need servicing or replacement.
any fault codes logged? check the wiring for idle switch and throttle body, its usually cooked around the back. sometimes sensors/switches can check out ok when probed, but fail intermittently when actually in use. I watched my idle switch measuring block while driving, and noticed it would randomly float open and shut while throttle was open, causing 'interesting' results also the latest issue I had was randomly the car would really hold back, even if I held the throttle to the floor. revs would sloooooowly build to about 3.5k then it would burst into life. this started happening more and more frequently, eventually getting to the point if it started happening and I opened the throttle too fast, engine would cut out. what really fried my brain was if i quickly cycled the ignition it would immediately fix the problem I tried disconnecting every sensor one at a time the ecu can live without, nothing helped. eventually it got so bad that cycling the ignition stopped working, and the car wouldn't even start again until after repeated cranking. turns out, it was the coolant temp sensor. the little bastard would always read fine in the ecu measuring blocks while i was watching it, I never did catch it in the act
Hi all, thanks for all the replies and suggestions, I did read them all and was working my way through the suggestions before I replied. GVK was on the money, the fuel pressure was sitting at 3.5 bar on idle dropping to 3 bar when revved. Once I replaced the fuel pressure regulator with a new Bosch part all was good. I took it for a nice 30 mile drive and the plugs were perfect after, unfortunately the crank position sensor I replaced was leaking like a sieve so I have had to strip it all down to get to that again! Taking the opportunity to do the cam belt and replace the coolant as it hasn't been touched in I think 8 years. And Jonny - to answer your question about codes, I can't get vag-com to play ball with it, think the 12v to the plug is missing. Another one for the list
