Closed Throttle Switch - Specific Question

[[steve]]

For months I've suffered from my 8v Digi jerking at low revs in traffic...

I replaced the dizzy cap, leads, plugs, cleaned ISV, TB, Checked all vac lines for leaks, rubber inlet boot for leaks, MAF tested best I can and finally the other week I stripped the injectors out and had them ultrasonically cleaned...

Now, it's still happening, so I had another extensive googling session and stumbled across the Throttle switches - the WOT switch works fine cause I have that 'extra travel' when I put my toe down and the car properly shifts once the pedal goes that little bit further.

I have had a look at the TB and throttle linkage this morning and my specific question is:

Should there be ANY play/travel BEFORE The closed throttle switch clicks on/off?

If I pull on the throttle cable there's a mm or so travel of the throttle arm away from the throttle stop before the closed switch clicks - is this normal?

I ask now, as I don't want to take off the TB to get to the switch etc i this mm of travel is normal?

I'm hoping this is my issue and if someone can confirm the switch should click AS SOON as the throttle arm moves away from the Throttle stop then I'll get the switch adjusted this afternoon - if someone could enlighten me on the procedure for doing that, it would also be appreciated.

EDIT - I found this link and it looks like it's referring to the Mk2 8v Digi TB from the images...

http://www.pvv.ntnu.no/~shane/stasj/pics/motor/dokumentasjon/A4-S4_B5/Fuel%20injection%20and%20ignition/AFC/MFI/24-73%20Closed%20Throttle%20Position%20switch%20checking%20and%20adjusting.pdf

Thanks in advance

Cheers,

Steve.

[Waspy]

Mine drives normally and has very slight movement before the click. Maybe a mm, maybe less.

Sounds like a vac leak to me, I know you said you checked but they can be easy to miss. When mine was doing this it was a split in the intake duct. I had checked it twice and missed it both times!

[[steve]]

Cheers dude,

Thought I would have a look and managed to round off one of the socket cap/allen head bolts holding the TB onto the manifold 

Quick trip to Halfrauds and £8 lighter and I have 4 new SS Socket Caps!

Anyway, yeah, everything seems to be set to factory (the yellow splodges of paint are on all screws on the throttle linkage/stop and on the CTS... will leave as is and put it all back together.... will have a good look for vac leaks...

It's the old story of it being fine when cold (assume as the choke is on keeping the revs up) but then it properly jerks when going onto/off the throttle... the mm of travel really made me believe that would be the issue!

I can't see how the CTS can be adjusted anyway.. the link in my OP doesn't seem to match visually to the CTS I have, so guess the link is for another VAG CTS/TB.

Thanks anyway dude, will continue the head scratching!

Steve.

[Brighouse-gti]

Front engine mount!! I say no more!

[[steve]]

Front engine mount!! I say no more!

How can I test that?

When I manually actuate the throttle in the engine bay the revs drop slightly before picking up... would this still be the front mount?

Also, would this change when the engine warms up as I don't notice the jerkiness when it's cold/warming up...

Just watched a YouTube vid - is it as simple as jacking up the engine and swapping out the front mount? I know the rear and engine/gearbox mounts are much more of a pain...

Thanks.

[Brighouse-gti]

I'd suppose the best way to test it would be to pop your bonnet and simply try and 'rock' the engine front to back. If your getting (what would have to be your best guess) excessive movement, then it would suggest failing mount(s). Changing the front mount is a piece of cake. Use a jack under the bell housing to take the weight of the engine, undo the nut that holds the mount to the front cross member, then simply jack the engine up (slowly) till you can free the mount and swap for new one. A new front mount should set you back £20 tops depending on brand. The rear engine mount is more involved and a rite pain in the a***, but the removal/fitting is basically the same.

Maybe the mounts aren't the problem at all, but it a symptom of what you describing, and it would be a cheap fix if it is!

[Brighouse-gti]

Front engine mount!! I say no more!

How can I test that?

When I manually actuate the throttle in the engine bay the revs drop slightly before picking up...

Actually if I'd have read that properly that does suggest a vac leak.
Do the revs hunt? ie, go up and down?

[[steve]]

Cheers guys,

I actually took the mk2 off the road in Jan 2015 for over a year due to the jerking issue. I got motivated again this year to get the injectors ultrasonically cleaned (and all seals replaced) after taking it to a local dyno place that were convinced it was the injectors....

After I refitted the injectors it seemed to be ok for  a week or so....

All vac lines were new from GSF in mid-late 2014 as I did a LOT of work to get the engine running properly:

New battery
new/reconditioned head
head gasket
water pump
cam belt
distributer (as hall sender failed)
leads
plugs
rotor
New blue + black temp sensors (in water flanges from head)
new oil sensor in side of head
crankcase pressure flying saucer thing seal
cleaned ISV thoroughly
Cleaned Throttle Body thoroughly
tested MAF/adjusted bypass screw - then set back to original position and makes no difference
removed idle screw, cleaned, replaced o ring and reset to original position

followed correct timing (blue temp sender removed and timed at 2000-2500 rpm)

Still jerking when going onto or coming off throttle...

I think I'm about done with head scratching so may sell, or take it to C & R Enterprises near me and have them sort it once and for all...

Cheers for the advice though

Steve.

[Waspy]

It sounds like you have done most of the stuff recommended, but don't fall into the trap of ruling problems out just because it's new.

I recently put a new fuel pump relay in mine, and it failed again a week later. I assumed it couldn't be the fuel pump again because the relay was new, but it was.

I wouldn't sell. Someone will have you over a barrel on the price because they know they can fix it for £2.

[Brighouse-gti]

Out of interest when you re-did your timing did you clear the ECU memory first. Also I'd check the crank breather for leaks as it may be sucking air in instead of letting the engine breathe. And, don't give up!!