Mk2 8v running issues, idle, power, revs limited etc.. any help appreciated

[bigdirtyturbo]

Hi there, first off what a good site this is. Happy to be back in a VW after about 8 years.

Recently i purchased myself a 1990 8v 5dr in what seems to be a not often seen grey silver.

All was fine but the temp gauge was tending to spend most of its time well in to the cold side of the gauge. This seems to be a common issue and replacing the thermostat and flushing the system cured my problem.

But when flushing i removed both the coolant sensors, which i didnt think would be a issue.

However after putting it all back together its been running really poorly.

I'll start with the idle.

The  idle with the blue ecm coolant sensor fitted will make the car fluctuate between 5-600 rpm to 11-1200 rpm and rev no higher than 4-5000 rpm, both on the road and when in neutral.

With it removed the idle will settle a little, but eventually it will start running really rough.

Ive checked everywhere  for air leaks and found a vacuum hose on the rear of the inlet manifold near the throttle body going nowhere , and cant see where it should of run to either??  it wasnt even blanked off i assume it has a purpose?

The icv vibrates constantly which i dont know is good or bad

The rocker breather is in good order no leaks anywhere there

afm is ok i think as if its unplugged the car stalls

In fact the only place i can hear anything that sounds like a leak is right at the throttle body inlet, but again there are no leaks i can find in the rubber induction tube.  and it isnt the un connected vacuum pipe at the rear of the manifold i found as i blanked it off for now until i find out what its meant for.

Do all gti's hiss at tickover by the throttle body?

Now what puzzles me is that i didnt touch a thing besides the temp sensors, so cant see how there seems to be a air/ fuel issue

Secondly

When out on the road the car has lost all power, it goes nowhere even with my foot down, driving under 2000rpm the car will pull itself along but if i want to accelerate it just seems to be holding back  quite badly. Im talking 3rd-2nd gear up a small incline.

Again im really confused what it could be, i only unplugged 2 sensors and plugged them back in once the job was finished. I have tried the "Rev 3 times over 3k" procedure but got no improvements.

My car ran beautifully before this and i kind of wish i had just left it as it was now

Any help would be appreciated and thanks for reading my small essay!

Dave

[theclash]

check theres no breaks in the wiring to the blue sensor
while the car is running fiddle with the wires to blue sensor you should hear idle  alter if theres a fault
might be worth buying a new blue temp sensor to rule that out get genuine from vw
try wd40 on leads dizzy and sensors
check all hoses round throttle body even the blanks they may be perished (about £2 a meter from gsf)
my guess is its blue temp sensor related

[Loynes]

Sounds like air my friend, I used some carb cleaner and sprayed it where I thought there might be a leak and found two, mine is a 16v which I believe suffer from leaks more.  You'd be surprised how changing one thing can disturb another, check check and check again sas motto.

[bigdirtyturbo]

Thanks for that, ill check over the wires for breakages. I ordered a new sensor from vw £20 inc the dreaded VAT...
I was thinking of replacing all the hoses because they are looking a little old now, but as i said i cant hear a leak or find one with the carb cleaner.
Do you know what the small pipe on the rear of the inlet is for? where its meant to connect to?

Dave

[CanisLupus]

Do you know what the small pipe on the rear of the inlet is for? where its meant to connect to?

Dave

If you mean on the rear of the throttle body, that one should be plugged. VW stuck about 10cm of vacuum hose on that and blanked it off with a little metal piece. As far as I know that vacuum port on US cars goes to a carbon filter and then on to the port to the front of the throttlebody, left next to the one which comes from the airbox. Not seen a UK carbon filter, not sure if that was done here?

But the rear one and the front (left port) on the throttlebody should be both blanked off.

[bigdirtyturbo]

Thats great mate, thanks. I'll remember to keep them blanked off when i change all the vacuum lines.

[Seanl]

Not entirely sure on the 8v, but on the 16v there are 2 vac pipes that run into the bottom of the intake pipe right by the the throttle body. As you can hear what seems to be an air leak, and you have a unknown vac pipe in that vacinity, check it out. 

[bigdirtyturbo]

Well..

I left the battery un-connected on the car over night just to see if anything happened. Earlier on today  i started the car and it ran fine until it got up to running temperature, then as before it lost all its power.

The revs dont seem to fluctuate any more it sits at just over 1k

Im almost certain now that the sensor im getting from VW on tuesday will sort out my problems, i would assume its  due to the temp sensor not giving the ecu a correct reading when hot?? does that sound right to anybody thats changed one before?

Checked all vacuum lines again and used a full can of good carb cleaner doing so. At least my inlet manifold and surrounding areas are now oil and grime free!!

[antogoof]

on the back of the throttle body there is a black plug, with 2 wires coming out of it, its your idle speed sensor. the wires connecting this sometimes snap. unplug it and look for any old repairs or if its cracked. mine did this and after 20 mins with a soldering wire its was right again. 

[Mr Blue]

Did you accidently fit the plugs to the wrong sensors? Dash MFA sensor and Blue ecu sensor have the same plug but colours may vary.

This shouldn't be enough to give you problems with massive power drains I don't think.


Welcome to the forum by the way. Watch out for Thom, JV and the other mods