mk4 tdi missing, cold start,ecu fault

[dyl_55]

Hi, can anyone help, I have a mk4 golf gt tdi 115 on an x plate.
If the weather is cold ie. bellow 14 degs c after starting the car it runs fine for about 2 mins then misses like mad ( un-drivable ) for about 3 to 5 mins then its ok all day.
I have taken it to every vw specialist I know and they can’t find any fault codes or problems.
The only possibility is that some one told me if the negative has been taken off before the positive it might have damaged the ecu. Is this plausible or will I be wasting allot more money?
Please help as I am sick of the car.:zx11:

[Col]

The most obvious one would be the water temp sender. These are notorious for failing and don't give any fault codes.

They fail so that the ecu is tricked into thinking the engine may be hot when it is cold.

The initial 2 minute running ok could be explained by the fact that the glowplugs will be engergised for the first 2 mintutes or until the revs go above 2k (i think). Try revving it above 2k as soon as you dare after start up and see if you get the rough running ?

The temp sender by the way is a nice easy diy fix.

Good luck.

[dyl_55]

Hi, If the temp sensor is the one near the top at the back of the engine, that when you take it out you lose a bit of water, then yes its been changed. That was one of the first thoughts of the vw Audi center and no sorry it made no difference but thanks for trying, any more ?

[Col]

I'd then turn my attention to the fuel system and check the security of all the hose unions as it sounds as if you may be getting air into the system. What may be happening is that overnight air is bleeding into the fuel lines effectively meaning that you are re-bleeding the fuel system every morning. The two minutes of normal running is probably the fuel in lines from the tandem pump to the injectors being used up, once that's gone your bleeding the system.

Pay particular attention to the fuel filter especially where the fuel stat fits to it with the two 'o' rings.