A KV problem.

[John.]

Excuse the daft questions as I'm a K-jetronic virgin.....although I did have a fling with a 2.8i Capri many years ago.
My recently acquired B3 90 has a running issue;-
Starts off the button when cold although revs a bit high........drives away fine but after running for a few minutes if you try and pull away it dies then kicks back in with a jolt. Once it's hot it seems to be ok but not always.
If you're stationary and you try and hold the revs at say 1500rpm it'll die down to say 1200 and then kick back in up to 200 and then die to 1200 and so forth.
Driving it like this is near on impossible.
........so I took this thing off, see below.(it lives below the air trunking between the airbox and throttle body)


I sprayed it's orifices with carb cleaner and checked the resistance between the two pins, 43.5 ohms. Refitted it but still the same, nevertheless I drove the car and then parked it up for about 20 mins. Tried to restart it but wouldn't fire, I suspect it to be over-fueling so left it for about an hour......then it started but maybe on 3 cylinders so I just kept the revs up till it cleared.
Anyway, I've now disconnected the plug to the above part and it seems to run fine........
......so, what is this bit? Is it at fault?
I haven't tried a cold start yet with it disconnected.
Gonna try and read up on the K-jet stuff but thought I may as well ask here first.

John.

[20vcqdriver]

Right if I am correct this effectively bypasses the metering head (attached from air box to intake hose to throttle body). If it is this one it is used to shut off the fuel to the injectors when slowing from speed with the throttle shut (high Vacuum) by letting the metering flap fully shut . Need to check how this is actually activated but will not cause much of an issue leaving it off and plugging holes, maybe just a couple of mpg worse off on short journeys...

[John.]

Originally Posted by 20vcqdriver

Right if I am correct this effectively bypasses the metering head (attached from air box to intake hose to throttle body). If it is this one it is used to shut off the fuel to the injectors when slowing from speed with the throttle shut (high Vacuum) by letting the metering flap fully shut . Need to check how this is actually activated but will not cause much of an issue leaving it off and plugging holes, maybe just a couple of mpg worse off on short journeys...

Thanks Dave, as it is just now it's fitted but the connector is unplugged......... would it be better to remove it altogether and plug the holes, is that what you're saying?
If this is the problem I'd ideally get a replacement.
Many thanks,
John.

[geneandbolly]

Originally Posted by John.

I sprayed it's orifices with carb cleaner and checked the resistance.

[John.]

Originally Posted by geneandbolly

I'll bet you've done the same in the back of an ambulance !!

[geneandbolly]

remind me the next time i see you to tell you about the girl who faked seizures and the unsuspecting colleague who attended her for the first time!!

[mikes2]

It's called a deceleration cut off valve.

It's shown on diagram MG 1 SG 33 Illustration 19-00 on the parts diagram

[John.]

Originally Posted by mikes2

It's called a deceleration cut off valve.
It's shown on diagram MG 1 SG 33 Illustration 19-00 on the parts diagram

Thanks Mike, and thanks for pointing me in this direction in the first place. I've checked the price against part no. on a few Audi parts sites.......about £80 !!....it'll be left disconnected for now!
I'm going to replace all the vacuum pipes in the engine bay as they're all the original braided type, pretty sure this'll have no effect but they need doing anyway.

[20vcqdriver]

Sounds to me like the valve itself is working as it shuts off OK when disconnected so you need to look at what is activating this valve as this sounds like where the issue is. I'll try and remember to get my drawings out tonight...

[John.]

Originally Posted by 20vcqdriver

Sounds to me like the valve itself is working as it shuts off OK when disconnected so you need to look at what is activating this valve as this sounds like where the issue is. I'll try and remember to get my drawings out tonight...

To me it's almost like there's a bad "track" in the potentiometer at a certain throttle opening, wasn't too sure if there was one 'cause with the engine off and you open the throttle from the closed position there is "no click" ??........ but it looks like there's a switch of some sort on the underside of the throttle body as there is a wire going there??
Should I hear a click ??........is there a potentiometer or switch?