mk2 8v injection with stalling problem

[gti racer]

Sorry for my first post to be a mechanical issue, but i've just got a mk2 golf GTI which I intend to race in the new 750mc golf race series and this problem is doing my nut!!

The car ( 1990 mk2 8v gti big bumper model  ) came off my brother and I know the history, it worked fine but needed a water pump and the temperature gauge in the car didnt work.

Changed the water pump and pulled the 2 sensors going into the head, one black one blue.  As they were so old the part numbers were indestinguishable, so got what the motor factors thought were right - this is where the issue starts.

Changed the sensors, temp gauge in the car works, but the car now stalls when you lift off the throttle as the revs dip too low.  Changed the blue sensor back to the old one, now the car wont start unless you really give it some throttle, so put the stalling blue back in, thinking I had the wrong blue sensor.  Went to VW asked for the correct "blue sensor" OMG, they couldn't work out which one it was    eventually they decided on the right sensor, ordered it (£15!!!).

Put it in today, and guess what, it stalls.

I found this thread http://www.golfgtiforum.co.uk/index.php?topic=56719.0  which is a similar problem, but as you can see I already switched the sensors.

So have I still got the wrong blue sensor or something else?

I also noticed there is a hole in the exhaust now due to a speed bump   , would this effect it.

And I also ran 1/2 a can of carb cleaner down the intake, ran a bit better, but still stalls.

Any ideas?

the car in question

[fused]

Mr RubJonny has posted this for digifants

http://www.golfgtiforum.co.uk/index.php?topic=33253.0

I also found this in another topic.... not sure which one, but here you go anyway

http://www.members.tripod.com/~fuelie/tuneup.htm

read through both and start with the easy bits first! Good luck

[Mr Blue]

have you connected the correct plug to the correct sensor?

[gti racer]

have you connected the correct plug to the correct sensor?

Yep, they are colour coded so couldnt make that mistake! 

[jaybv6]

rubjohnny has suggested that people use the genuine blue temp sender from VW rather than those from motor factors etc as they don't tend to last that long. 

[rubjonny]

check your idle switch clicks with the throttle closed, and that the wires round the back of the throttle boddy havent snapped.  The idle switch is underneath the throttle body, you can only get to it with the inlet boot removed!  If it does not click 1st check the adjustment of the throttle cable, the throttle linkage should hit up against the stop firmly when released.  If that checks out, you need to loosen the switch or linkage screws and move it so that the switch clicks just as the throttle is closed.  Which screws you undo depends which ones you can actually reach