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I have had my Golf for 8 years. It’s had good maintenance and a the record is kept by my dad. It’s just passed its MOT (Ministry of Transportation) test, and the mechanic mentioned that the tappets were sounding a little loud, so my dad who services and does work on my car flushed something through the oil and did an oil change afterwards to see if it would help.

It was quieter for a few days after, but is it a coincidence that when I start the engine I now get juddering, and also grey smoke from the exhaust until the engine had warmed up properly? My dad is a good mechanic and he is mystified by the smoking, and now considering if the engine is on its way out.

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What year is the car, or what generation Golf precisely (consult WikiPedia article to identify the generation)? –  theUg Jun 17 '13 at 15:42
    
2000 w reg golf GT TDi –  Charlie Jun 17 '13 at 21:38
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"Juddering" is as good a description as any of how a diesel runs when not all cylinders are firing. Gray smoke from the exhaust is unburned fuel (i.e., it has been injected into a cylinder, mixed with air, but not burnt).

If your Golf is new enough to have a catalyst (many VW diesels are), then unburned fuel in the exhaust will quickly damage it, so you want to fix this. However, it's much too early to give up on the engine! Most likely, one or more of your glow plugs have failed (so they don't heat up the cylinders and promote ignition when the engine is cold), or the system that turns them on at cold start is malfunctioning. I can't give more details without knowing how old the car is--on older diesels ('80s VWs and Mercedes, for instance) there is a simple relay that can easily be tested, while on newer ones (VW TDIs, for instance) the glow cycle is computer-controlled.

EDIT: If you can rule out the glow plugs, there are a number of other less likely possibilities. Anything that restricts fuel or air flow on a diesel engine can cause incomplete combustion (and hence, again, gray smoke). This would include clogged fuel or air filters, for instance. The fact that your car is a 2000, though, makes me think of one particular common problem with VW TDI engines from 1999-2003 or so: soot buildup in the EGR system. Fixing this requires removing the EGR valve and intake manifold and soaking them in solvent to clean out the soot. It is a simple job but time-consuming (and therefore expensive if you have to pay someone else to do it, unfortunately).

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It's w reg year 2000, glow plugs have been changed3 out of the 4 were not working. –  Charlie Jun 17 '13 at 21:35
    
That was done 2 weeks ago and hasn't affected or changed anything! –  Charlie Jun 17 '13 at 21:39
    
If it is comp-controlled, would it not throw an error code? –  theUg Jun 18 '13 at 0:16
    
@theUg: Yes, US models usually but not always will turn on the Check Engine light when the glow plug resistance checks wrong or uneven across the four. I don't know about the equivalent in other countries. For what it's worth, here is a thread about glow plug problems on TDIs that suggests that the harness can easily be damaged or the connectors to the plugs dislodged when servicing them. Sounds to me like it's possible that one or more of the plug wires wasn't securely attached to the plugs when they were changed and has come loose. –  dodgethesteamroller Jun 18 '13 at 0:29
    
I just don't have time to maintain the car anymore if I sold it how much would it cost someone to get this looked at at a garage? Any idea of tge market value? Thanks –  Charlie Jun 20 '13 at 8:10
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