Annoying off throttle jerk!

[Critical_Mass 10]

Hi all,

 

For a while now my VR has had an annoying jerk when coming off the throttle, even a small jerk when applying - but not always noticable. It makes driving in traffic frustrating and general driving the car no fun at all.

 

Ive changed the front engine mount and it was rather worn, but it didnt improve - though going to check it to make sure all is well. Other than the engine mount and the throttle bamper, what else can cause this?

 

There was a thread not long ago that suggested this was a VR charactaristic but im positive this hasnt always been like this.

 

Any ideas of things to check, its driving me mad!

[davidwort 0]

Throttle cable smooth? Throttlebody clean? Could be a vacuum leak on inlet side, or perhaps fuelling related - possibly lambda issue, worth getting the lambda signal checked out on diagnostics. Just a few thoughts.

[Critical_Mass 10]

Throttle cable smooth? Throttlebody clean? Could be a vacuum leak on inlet side, or perhaps fuelling related - possibly lambda issue, worth getting the lambda signal checked out on diagnostics. Just a few thoughts.

 

Ok, i'll check the pipe work over the weekend and get vagcom plugged in. I'll also give the TB a clean out.

 

The throttle cable itself seems ok, i mean its not hard to apply throttle. But i'll check it out all the same.

 

Cheers David.

[Roger Blassberg 0]

Could also be a MAF or ISV issue; I had the same problem when mine went through a phase of rough running, unstable idle and stalling. Also check that the dashpot on the throttle body is damping the throttle closure properly - if it is dropping closed suddenly that may be your problem. Those dashpots are stupidly expensive from VAG; I bought a spare TB on ebay, complete with dashpot and throttle position sensor and cannibalised it for parts.

 

Have you had the battery disconnected recently? If you have, do a basic settings to coordinate the throttle position sensor with the ECU.

 

I checked out the ISV and cleaned it, made sure that there were no vacuum leaks, changed the MAF for a known good one and (most effectively) cleaned the contacts and reseated the 42 pin connector on the side of the cylinder head which deals, amongst other things, with signals to the injectors and the ISV. It now runs very much more smoothly and that lurching at very low throttle openings has disappeared. And the stalling problem seems to have gone away too..... Famous last words.

 

Best wishes

 

RB

Edited March 30, 2012 by Roger Blassberg
additional info

[Critical_Mass 10]

Well the idle is fine, its not rough, but yeah a lurch at low throttle openings is there. I'll strip the ISV and give it a clean along with the MAF plug connectors. i hope the MAF itself isnt the problem though! I'll try unplugging it whilst its running and see if it makes a difference. Can rule it out or not then.

 

Is the connector on the side of the cylinder head the cylindrical oen on the right next to the coilpack and aux water pump?

 

can you clean the MAF with anything, carb cleaner etc?

Edited March 30, 2012 by Critical_Mass

[Jim 1]

Apparently you can clean them but any cleaning is normally a temporary measure - once the MAF is on the way out, that's normally it and only a brand new one will give you any permanent results :(

[Critical_Mass 10]

I'll fire some Carb cleaner into it whilst running. Wasnt sure if id burn the wire inside.

 

I hear what youre saying Jim, but knowing how expensive they are i dont want to replace it if its not the cause.

[Roger Blassberg 0]

Yes, the connector is the big cylindrical one near the coilpack. Quarter turn anticlockwise and then it pulls off. I gave mine a good spray with contact cleaner on to both sides, then let it dry and reseated it. Also spray the wire inside the MAF and the six-pin connector. They are supposed to self clean when you switch the ignition off.

 

Best wishes

 

RB

[Critical_Mass 10]

Ok cheers Roger :salute:

[Jim Bowen 1]

When i asked about this in the past i was told the throttle damper cushioned the throttle lever as you release the accelerator.

 

Just taken my throttle body off and this damper thing has a seal thats all split and perished i dunno if this does much

[Critical_Mass 10]

Yeah im not sure how much it does either, but it must do something. In could it be the throttle cable isnt adjusted correctly. Any ideas how far down the cable the pin should sit?

[fla 9]

if its split, if you open the throttle butterfly and then let go it will slam fully closed. If its ok, when it hits the seat on the dashpot it will slowly close the flap.

[Critical_Mass 10]

Thanks Hasan, i'll check this also. The list grows!

[Chris Langdon 0]

interesting as mine does this at low speeds in traffic, think il do the same;)

[Critical_Mass 10]

Its the same jerk you get when the front engine mount is worn but its been changed about 6 months ago.

[RW1 0]

Its the same jerk you get when the front engine mount is worn but its been changed about 6 months ago.

 

Bolt hasn't worked loose has it?

 

.

[Critical_Mass 10]

Ill check tomorrow. There's no clunk when it jerks just movement

[efil4sbuD 0]

If you decide that it's the MAF then I have a new one kicking about somewhere. I had troubles recently and bought it but I found that it wasn't the problem so I put the old one back on.

 

James

[24V Renshaw 0]

I would check the damper first, all points to that for me.

 

Jay

[Critical_Mass 10]

Cheers Efil. Didnt get chance to look into this over the weekend, but i will bank hol weeked.

[Critical_Mass 10]

Right an update.

 

Cleaned ISV, cleaned all pipe work with carb cleaner. I also cleaned the throttle body in situ as one of the allen key bolts had rounded off enough to stop me getting it off - typically its the one hardest to get to. So at some point i'll have to take the inlet mani off to get to it and replace the not.

 

I also checked the damper as suggested and i think that does need replacing as it doesnt cushion the throttle at all it just slams shut. So if anyone has one, i'll take it.

 

To be honest, when i think there's 2 issues, the throttle slamming shut causing a jerk, but also the car just doesnt feel right to drive at the mo, putting the off throttle jerk to one side the car just seems juddery/lumpy in general and im not convinced its engine - it just doesnt ride very well. Its like a feeling of going down a cobbled street all the time, but not quite as extreme, its subtle - can worn top mounts cause?

[Critical_Mass 10]

MAF is working as i discovered today. vag com plugged in, no faults. I can only think its drive train related. maybe wishbone bushes or top mounts. other than that im out of ideas

[CazzaVR 0]

The MAF won't necessarily throw a code though, even if faulty...

 

I've got similar symptoms to you and think it's almost certainly the MAF. Been like that for a while, but has got steadily worse, and it's even started stalling and idling too high etc. Have unplugged it and noticed no change in the engine note etc :( I'll let you know if a new one cures it.

[Critical_Mass 10]

I pulled the plug on it too and the engine almost stalled before i put it back in. So it is working. It threw a code up due to me unplugging it also.

 

To be honest i dont think its engine related, more suspension... but not sure what.

[24V Renshaw 0]

Could well be wishbone bushes if they are really tired. Probably exaggerated by the throttle damper not surpressing the "on/off" loading.

 

Jay