Please Please Help my newly aquired MK3

[mpgscott]

Bit of a long story I'm afraid.

Yesterday i managed to get a very clean 1992 K Reg 5dr Mk3 Gti 8v and it is in really good nick 2 owners from new and only done 78K FDSH verified by VW excellent buy i thought.

The car had been very spluttery and i put this down to the fact the previous guy had recently fitted a K+N induction Kit.  So i removed this to put back on the paper air filter assembly, although i did not know where the bottom pipe (black one) on the air box connects to i just blocked this off.  The car was still very spluttery.  I have to do a journey of 190miles twice a week to my job.  Today i took off in the golf and felt the car was very spluttery as you let off the throttle in any gear to come down in speed.  This gradually got worse, until the point after around 85miles where the car was nearly not going at all.  I pulled over and the car stalled and would not start it would sometimes nearly get there but would not run.  So i called the breakdown company.  After leaving the car off for around 15mins i re-started the car and it ran perfectly revving up to around 4-5000 no probs left it to run for a few minutes and then called off the breakdown. 

Now i noticed that the cars coolant gauge was only going above the four lines before 70 degree mark while driving the car always the same.  As i let the car idle at the side of the road i watched the gauge go upto 90degrees and the fan cut in.  As i drove off again the gauge went down to below 70 and just at the 4 lines.

Now am i write in thinking that the gauge and ECU use the same sender so if the thermostat is stuck and the ECU has two engine temp readings would this cause the problem.  At the end off the cylinder head as you look from the front i disconnected the sensor and i think this made a difference, but after a while i reconnected it and the car still ran ok.

Anyway i carried on and did the remainder of the journey another 100miles and the car seemed ok although it was very spluttery as you let off the throttle in any gear.

Can you please tell me your thoughts as to what is causing this? and also if possible where the black pipe from the airbox goes pic if poss would be much appreciated

Many thanks Mark

[monkeyalan]

bad running sounds like the common problem seen all over this forum. ECU and /or fuel pump relays. about £30 -£40 from the dealership.
Not sure about which pipe you mean. my airbox only has one in(from the front ) and one out ( to the throttle body.

the gauge sounds about right. Oil temp on the MFA should be about 90 when fully warmed up.

hope this helps 

[mowgli]

I reckon that you've got the thermostat stuck wide open which would give you the gauge problems you describe.  Whether or not this would affect the engine I'm not 100% sure, but, the ECU is being told the engine is cold so is running the car this way.  My guess would be some sort of over fuelling, whats the fuel consumption?, I guess its showing in the high 20's tot he low 30's on the run?  HTH.

[mpgscott]

Over 180miles i averaged 36.6mpg but when the car runs poorly there is an awful smell of petrol so i would think it is overfuelling.

Thanks
Mark

[bampotman]

My car was the same a while ago except for the spluttering. The temp would rarely get above 70 but when in traffic or standing it would get to 90. I changed the thermostat and its fine now, always at 90. I would change the thermostat if I was you. The only thing is that my car never spluttered. It did use to stall when cold but I cleaned the throttle body at the same time as the thermostat and I think it was due to that.

btw the thermostat is a bi*ch to get to especially if you have ac

[GTI EDITION (aka LTD)]

It could be the digifant ECU control unit supply relay* sodding about , I had the similar problem with mine . it seemed to have a mind of its own as it was very sporadic and every time I was in a position to check it out it started to behave its self 
I eventually managed to catch the bu99er out and found that when I tapped it the engine ran perfectly ,so I fitted a new one and since then I've had no futher probs.

* relay J176 situated in position 3 on the relay plate 

As regards to the black pipe ,if it's the one facing backwards on the lower half of the airbox ( about 2 inches in diameter ), then it's most probably the hot air pipe that connects via a hose to a flange on the exhaust manifold