Jerky At Low Speeds - Wisdom Required

[feb 47]

Just came back from SBC, knackered after 4.5h drive and traffic jams. The car is much smoother now although the 8V will always have some jerkiness, it is just that I have not lived with the car for 1.5 years now...

Anyway, during the RR tune Paul adjusted the AFM and TPS, set the fuel pressure to the original setting (previous owner has fitted a gimmick FSE one), ignition etc and the car drives much better now and idles smoother.

As Grim Badger said worn engine mounts and buffers contribute to the jerkiness. The buffers on the side of the engine (don't know what they are called) are not available anymore but metal plates can be welded in the gaps to prevent the engine from moving.

Edited June 19, 2009 by feb

[Miles 331 1 Cars]

The key is setting them up right which not many people can do although on paper it looks quite simple, I've got a very old Snap On Diag tool for the Jetronic so basic you need to remove the ECU and plug inbetween it but it does then give you a reading of the AFM, Injectors, SAD, CPS etc

I don't come across many 8v's now but the last one I did I had the owner on the phone saying how nice it was to drive and I must admist I thought the same, 950 rpm Idle with or without load, No Kangarooing and no stalling hot or cold.

The lower engine mount can be a big factor as they don;t last long with all the oil and stuff down there

 

Feb, You can still buy the buffer's without any problems at all, So not sure why they said that

[Richie-Van-GTi 70 2 Cars]

I agree with Miles, its all down to set up. No need for fiddling with TPS etc. All the ones Ive had that have been jerky have been cured by setting the idle up from scratch. Most of them over theyears have had a twist here and a screw there to adjust into the wear and tear of daily use. Result has been a bad combination of throttle stop screw, idle screw, dizzy and AFM adjustment. By cleaning it all out then starting afresh in the correct order I have eliminated the problems. I always set the throttle stop first so the throttle butterfly is only just off the throttle housing, then set the TPS so its just switched off at this point. Then set the idle screw, usually by winding it right down then back out about 2.5 turns. From this point its a case of getting your dizzy timing right combined with the AFM. You sometimes need a half turn on the idle screw in either direction just to tweak it. Depends on the engine health. Aim for a solid 900rpm idle when warm.

[d7ve_b 44 1 Cars]

Just came back from SBC, knackered after 4.5h drive and traffic jams. The car is much smoother now although the 8V will always have some jerkiness, it is just that I have not lived with the car for 1.5 years now...

Anyway, during the RR tune Paul adjusted the AFM and TPS, set the fuel pressure to the original setting (previous owner has fitted a gimmick FSE one), ignition etc and the car drives much better now and idles smoother.

As Grim Badger said worn engine mounts and buffers contribute to the jerkiness. The buffers on the side of the engine (don't know what they are called) are not available anymore but metal plates can be welded in the gaps to prevent the engine from moving.

 

If you don't mind me asking, how much did the work at SBC set you back? PM me if you'd rather not post it.

[CosKev 16]

If you don't mind me asking, how much did the work at SBC set you back? PM me if you'd rather not post it.

 

Just over £50 for rolling road set-up/power results with no parts

[feb 47]

As CosKev said, 50 pounds for the RR setup. What I have noticed though is whenever SBC set the car up, you can definetely notice the increaser in power and torque and the warm idle is a lot smoother but my car will now stall when cold. It didn't do this before so it's either the higher fuel pressure that helped it previously or something else that I don't know. I am fed up now having to trade a cold idle for better performance across the rev range and just raised the warm idle to 1500 rpm with full electrical load on so I hope the cold will be OK tomorrow morning. I know this is a 'boggo' fix but I have neither the time nor the tools to fiddle around, I just want the car to have a steady idle when cold as it's the wife who drives it now and don't want her to start hating the car, I hate it enough myself now.

Miles, the diagnostic tool you have sounds good, I will need your help to setup my car as I am fed up with it and was suggesting to sell it(!) but it's the wife who wants to keep it now as she gets compliments about it wherever she goes.

Is it worth replacing the SAD before trying anything else?

Rant over

Edited June 20, 2009 by feb

[Grim.Badger 15]

Adjusting the TPS works though,stops the jerkyness alltogether,has no other side affects on fueling or the way the car runs

 

Have you driven a car that has had this done to the TPS????????

 

I think you would soon change your opinion

 

My point was that it doesn't mater if the car drives better, it's still avoiding the problem

[johnsimister 10]

Clearly it's vital to have everything set up correctly, no air leaks, distributor not so worn that it's advancing too much too soon (weak springs), etc etc. If after all that it's still snatchy, with that surge as the overrun fuel cut-off reinstates the fuel, you could do as I did and get Superchips to modify the ECU.

 

It doesn't increase ultimate power to any detectable degree, so ignore those claims, but what it does do is alter the cut-off characteristics so the fuelling is reinstated gradually instead of a sudden torrent. It completely transformed my car, which will trickle right down to idle speed and pull away again without a single snatch and without touching the clutch. IMO it's one of the best mods you can make to a 205 GTI.

 

John

[chocolate_o_brian 0]

Hmm, fo some reason I didn't get any email notification of these replies, so apologies if I have looked ignorant to them

 

I think my best course of action is to have the car properly set up.

 

Johns seen it in the flesh, as has Grim Badger (sorry forgot your name), and Rich205 who pm'ed me asking for advice. has a similar problem.

 

I've changed various components and hopefully will be having a faff with Monsieur Badger sometime this week. I still have the jerky drive and know my mounts are slightly worn, but I put most of it on needing setting up by ear by a specialists. For around £50-60 it sounds very good value for money (in comparison to having my old Impreza tweaked anyways).

 

Thanks again for the replies and hopefully others will find it of use.

Edited June 21, 2009 by chocolate_o_brian

[CosKev 16]

My point was that it doesn't mater if the car drives better, it's still avoiding the problem

 

So what problem have I avoided???????

 

New cars don't cut the fuel, doing so burns out the CAT apparently, they just run with very little fuel.

 

Adjusting the TPS is cheating and you may as well remove it entirely as it is a SWITCH not a sensor so it only knows when its shut, it doesn't tell the car how far open it is. Its only purpose is to tell the ecu that the throttle is shut so stopping it doing this is kinda stupid.

 

In my experiance jerkyness is caused by:

 

1 - Worn/improperly fitted engine mounts New Pug top eng mounts,BBM solid rear mount

2 - Old AFM with a worn carbon track Remanufactured AFM

3 - Badly adjusted throttle cable, or the cable is catching on something New Pug cable,routing checked and adjustment

4 - Badly set up AFM Remanufactured AFM

 

New plugs, leads, filter etc won't stop this, although they may help with other related problems.

 

[welshpug 1,626]

poor setup, worn dizzy,

[CosKev 16]

poor setup, worn dizzy,

 

Dizzy is slightly worn,but not enough to effect the way the car drives just short of a couple of degrees of advance at the top end

 

Poor set up of what????????

[welshpug 1,626]

if it kangaroos, everything!

 

you CAN set them up properly without any bodges like setting the switch wrongly, what you have to remember is that if you set the switch so that it doesn't get the idle signal, it'll also get the full throttle signal far too early.

[CosKev 16]

if it kangaroos, everything!

 

you CAN set them up properly without any bodges like setting the switch wrongly, what you have to remember is that if you set the switch so that it doesn't get the idle signal, it'll also get the full throttle signal far too early.

 

Car runs spot on now after RR at skips which included the TPS setting.

 

According to Grim Badger the TPS only tells the ECU when throttle is shut so no full throttle signal

 

Adjusting the TPS is cheating and you may as well remove it entirely as it is a SWITCH not a sensor so it only knows when its shut, it doesn't tell the car how far open it is. Its only purpose is to tell the ecu that the throttle is shut so stopping it doing this is kinda stupid.

[boombang 2]

TPS has 3 states:

closed throttle

open throttle

wide open throttle (comes on from about 90% throttle up)

 

Makes a marked difference to acceleration when WOT part is working right.

[welshpug 1,626]

explain why it has three wires then?

 

also check section 22 of chapter 13 of the haynes manual, where it says how to check the operation of Idle position, as well as WOT.

[CosKev 16]

explain why it has three wires then?

 

also check section 22 of chapter 13 of the haynes manual, where it says how to check the operation of Idle position, as well as WOT.

 

Do you know what the TPS settings alter via the ECU????

 

As fueling/timing etc was set up on my car and checked throughout the load/rev range with TPS set up as Skip Browns do with no adverse side affects??????

[feb 47]

I think what boombang says is correct, the TPS is not a potentiomenter but a switch. SBC mentioned that when you have WOT, two electrical contacts are closed which cause fuel enrichment needed for full throttle.

[boombang 2]

I think what boombang says is correct, the TPS is not a potentiomenter but a switch. SBC mentioned that when you have WOT, two electrical contacts are closed which cause fuel enrichment needed for full throttle.

 

Spot on. It's basically a springy piece of metal. Doesn't click when activated, but opens the circuit between centre output on TPS and the other side terminal. Assume this then makes ECU increase injector duration, although to what extent I have no idea. All I know is comparing a friends 205 Gti with it to without it was like night and day, really felt the difference with it working.

[Grim.Badger 15]

I didn't think it did anything at WOT, but stand corrected Will have a play with mine sommtime to see if it clicks at WOT as well as shut throttle

What's the point of it doing anything at WOT anyway? Surely it can't restrict fuel as that would cause the engine to run lean

[Grim.Badger 15]

So what problem have I avoided???????

 

Well there's obviously something wrong, they didn't come out of the factory like this....

[welshpug 1,626]

IIRC when at WOT it'll just give maximum fuelling ignoring the AFM input, or something to that effect, making it hot WOT too early can be harmful to the engine due to bore wash in extreme cases.

[Grim.Badger 15]

IIRC when at WOT it'll just give maximum fuelling ignoring the AFM input, or something to that effect, making it hot WOT too early can be harmful to the engine due to bore wash in extreme cases.

 

That just sounds stupid, not that I don't believe you afterall they are French

[chocolate_o_brian 0]

I've started a mass debate

[welshpug 1,626]

That just sounds stupid, not that I don't believe you afterall they are French

 

 

that bit is actually German