Hi, welcome to Just answer, my name is Ross, i will help with your question.
Is this something that suddenly started or has it progressed over time?
well i had a problem with the oil pump so changed it and as mentioned few other things and now this
i changed the engine block because when i removed the sump i noticed a thrush washer in the oil so i thought better to change than put everything back and find more problems
Right, have you checked the crank case breather hoses? these block up with gunk on these engines and cause this to happen.
i did clean them when i took engine out butthey may need another good clean is there anything else it could be
Throttle body position sensor, these can cause bad running, often dont show a fault as it gets a signal to the ECU but its not accurate, Engine coolant temp sensor, again these are very common and dont always loose signal to bring up a fault, it just gives the wrong reading.
These also suffer with bad piston slap and i have known them to damage the piston rings and/or cylinder walls, but compression is good so i wouldn't worry too much about that.
ahh right ok it does warm up rather quickly i have another golf which runs fine but takes ages to heat up. i did think piston slap but as you say compressions say things are ok and i would have thought emissions ould have shown something too.
would the coolant sensor seriously give all this trouble.
Yea, coolant temp sensors cause all sorts of havoc on these engines, in fact most of the VW range seem to suffer with it, i have known them to completely prevent starting when hot, these are the plastic 4 pin clip in sensors, they all have different colour rings on them, often people fit a yellow sensor when its supposed to have blue or vise versa (i forget the correct colour) but they assume they are the same, so it works perfectly well as far as the ECU thinks, but its giving the wrong reading.
Emission control is also quite good on these engines so it goes a good job or correcting the emissions but this is a trade off for smooth running giving the problem your having.
right that makes sense if i were to unplug the coolant sensor would this temporarily make it run better i know it would probably throw up a code but just a way of testing
Yes, the ECU will revert to basic mode, where it guesses the engine temp, its not an accurate way of telling as with it disconected, it may well give the problem you have already, but its well worth trying as it may throw the ECU the other way so it increases emissions but the engine runs better, if this happens its going to be the sensor for sure.
wow, i have been working on this bloody thing for weeks and being a mechanic i tried everything and its nice getting another opinion.
No problem, try the sensor, its not something people suspect to cause such problems but if you do keep having problems, feel free to come back here and i will continue helping to get to the bottom of it.
ok just tried it didnt make difference
Right, its not a conclusive test, so keep the sensor in mind. Is this more of a misfire or is it just lumpy on idle.