idling problem... help me plz!

[cloak]

hi guyz,

im from south africa and recently bought myself a '99 citi golf (mk1). and im having serious idling problems with my engine (carb)! -and it really gets on my t*ts. ive had numerous people hav a look at it with no luck. not even VW themselves can help me.

basically my prob is this. when my car sits and idles without touching or doing anything, it idles fine. but when i drive in traffic or whatever, basically whenever i stick my foot on the brake pedal, it wants to cut out and most of the time it does! the revs drop right down. and it REALLY gets to me, hence i hav to use my handbrake all the time in traffic so i can stick my foot on the accelerator to prevent my car from cutting out. ;( and if i slam on brakes from high speed while in neutral it just dies straight away.

i figure its got something to do with the pressure from the engine that the brakes use? ive had my carb cleaned and even did the method of swapping the two spark plugs round -causing the car to backfire and clean out all the crap in the carb. cleaned out everything and fully serviced my car.... just cant figure it out ;(

so im hoping theres someone whos had the same problem as me and thats clued up with engines more than i am...

cheers
c

[berendd]

check your vaccuum system. Follow the hose that leads to the brake booster, about 1,5 cm's from the air inlet you'll find a T-piece with some tiny hoses on it, check if these hoses are atached to the carb and not hanging loose.

If you want to check if it's the brake booster itself, take the vaccuum hose from the booster and stuff it, so no air can get in. then try if the engine runs better (in a safe place since you have no brakes).

the last thing you could check is the carburettor flange, which fits in between the inlet and the carb. This flange is rubber and tends to cause problems. Succes and keep us updated.

[cloak]

thanks for your reply berendd ;)

the brake booster runs off pressure from the exhaust system right? excuse my dumbness not toooo clued up with all this. could u maybe explain to me a bit better how the whole brake booster system thing works? i dont see how a lose pipe would cause my engine to die.

carb flange is perfect..

[berendd]

doesn't run on exhaust pressure..

does run on vaccuum from the inlet. so if it leaks the engine gets too much air, because it doesn't flow through the carburettor. then it dies.

[gunny]

I'm new here, but a little info in brake systems, the brake booster operates off of manifold vacuum, that being said, it's a "one" way line, there should be a small check valve in the line coming from the manifold, or attached directly to the booster itself. A good way to check for vacuum leaks around the manifold is with a can of WD-40, get the car running, and then spray it around the manifold base and anywhere else you may suspect a leak, you will notice the change in engine rpm very quickly. A fast and dirty way of tracking vacuum leaks. Hope this helps.

[sjampoo]

@Op:
There various things that could cause this problem. The brake-booster could be it.

To solve the problem, there are a few extra questions:



- On the highway, in highest gear: push the clutch down (an nothin else): How does it return to idle?
It should do something like this: fall down in revs from aprox 4000 rpm orso to 2000rpm quickly, then slowly return to idle speed of about 1000 (or whatever).

If it falls down from 4000 to 500 or even 'dead': Check timing, vacuum-advance system (mushroomshaped thing on the dizzy) etc etc.

Same test: if it idle's ok, going down from 4000 to about 1000 rpm, does it stall directly if you only 'touch' the brake a little (very very slight decelleration), or does it stall only when you brake (and de-cellerate from say 80mph to 40 in 5 secs).

If it only stalls on de-celleration: check your carbs ' brake-air-system-jet ' : the petrol in the swimmer-chamber is pushed forward (braking-G-force), and thus the idle-jet isn't supplied with enough pertol, the engine doesn't get it's proper mixture, and stalls.
--> If the brake-air-system-jet is functioning, It could be the carb flange.. (if it looks ok, it could still be ' leaky '
==> Flange test: let the engine idle, and push the carb to tillt it a little (forward, reverse, and to the sides: if the idle speed changes: vacuum leak

If if dies directly after touching the brake pedal.. it'll probably be the brake-boosters-check-valve..
although, it shouldn't be a problem: The check-valve that should make it a one-way system. If this valve fails, there will be a vacume loss when the brake is pressed,.. true. BUT: I drive a 1991 car with faulty check-valve, and it doesn't give me any problems what so ever... (only thing is: all brake-boost is lost directly when the engine is stopped. (doesn't stall on braking)).

[cloak]

thanks for the reply sjampoo, i will test a bit today on the way home from work on the highway. ive had no luck lately with the problem... been so busy with work. but i will let u know what happens! nice to hav a place to ask questions like this to fellow veedub enthusiasts...

thanks,
cloak

[sjampoo]

Good Luck,

Haven't been 'all that' in my spare time either: Christmas was only 1 day off work, newyear 'zero'.. so only work and private obligations (not a bad thing though) in the weekends took all the dub-time away.