Violent juddering at very low speed/rpm

[Adamstanford 3]

Hey there. Usually when pulling off in 1st or 2nd at low revs (when trying to be gentle etc) soon as you release the clutch it'll start kangarooing and jerking as if you're stabbing the throttle. 

 

Tps seems set correctly. How do I clean the AFM? No air leaks and it drives and idles perfect all the rest of the time

[Adamstanford 3]

MOT has revealed it's running a bit lean. At idle it's 0.48% co.

[DamirGTI 342]

Idle mixture is separate to the rest of the rev range .. meaning while idling air mostly bypasses the AFM flap measuring and going through separate passage .

 

But yes , been experimenting with that while monitoring WB gauge and tweaking the mixture rich-lean .. as soon as you start adjusting it more on the lean side it starts to "misbehave" , drive increasingly badly while on-off the throttle , jerky , kangarooing , shaking etc. .. contrary when you start to richen up the mixture it smooths up to a point where the transition on-off the throttle is barely noticeable (as much it can be "smooth" on Jetronic .. can never make it perfect on Jetronic) .

 

Open up the black plastic cover on the AFM , and see if there's any damage on the potentiometer carbon track .. look for any white areas or dots on the black surface or excessive grooves .

Typically carbon track gets damaged (wiped out) on 1/8 to 1/4 the area just above the wiper arm rest point .

 

Ignition timing also impacts this "snappy" on-off throttle behavior , make sure the dizzy is in good working order and that the timing is adjusted properly .

 

There's no universal solution to this i'm afraid , but combination of a few things that needs to be set , adjusted , checked out .. fuel mixture , ignition timing , TB adjusting , etc .

 

 

D

 

 

Edited January 21, 2021 by DamirGTI

[Thijs_Rallye 87 4 Cars]

As @DamirGTI states it is likely a combination of factors. Jetronics aren't exactly renowned for their smoothness.

 

With this kind of off-idle transient response I would check the vacuum at the take off pipe below the throttle valve. If my memory serves me right there is a vacuum level to which the throttle opening has to be set in mm Hg in the Haynes manual. Furthermore you could check if your vacuum advance membrane is still intact, as well as if the centrifugal advance mechanism is still working as it should (not likely tbh). If this is all OK you can re-set your ignition advance as per manual.

 

In regards of the AFM those usually wear out at the part throttle spot on the carbon track (which is a different spot in my opinion), it will be worth checking it anyhow and re-setting the wipers to a better part of the track.

 

The Jetronics are finniky to setup right but again, they were never really smooth to begin with. Hence my preference for the Motronic M1.3 (DKZ)

 

[DamirGTI 342]

Agreed , shame really all of them haven't been mass produced with Motronic 1.3 or Motronic  3.1 .. so much better engine managements and yet they fitted it on just a small scale of Peugeot/Citroen models , like Citroen ZX 1.9 Volcane - haven't seen one for more than 17 years !

 

 

D

[Adamstanford 3]

On 1/22/2021 at 1:20 PM, DamirGTI said:

Sent the car off to be looked at. Now Co reading at 3% and has correct afm fitted (was an incorrect one) 

Still pure jerky at pulling off rpm. All gears. Even a small pothole can send it into a frenzy, the throttle is way too responsive.  Apologies for the format of this reply it'll only let me reply as a quote for some reason when I click reply. 

 

So, how do I smooth it out? Make it a bit less responsive. 

[Adamstanford 3]

On 1/22/2021 at 1:20 PM, DamirGTI said:

Wish this forum would just let me reply as normal. 

So to be clear, it's jerky as hell at part throttle, any speed really. WOT is fine and idle is good also. 

 

I've had three of these and none were ever this juddery on the go. Speeding up and slowing down, fine. Trying to maintain speed or pull off smoothly? Forget it. 

 

I read somewhere about someone setting a TPS (woodsy) so it doesn't click when you first open the throttle? I thought it Was supposed to? 

[309SRiguy 15]

Are your engine mounts in good condition? A worn out bottom mount can allow a lot of engine movement when moving on/off or off/on the accelerator. It can result in transmission snatch that feels quite violent at times.

[DamirGTI 342]

As said , it's the "nature" of the engine management .. some are better some worse , depending how good or bad they're set up and in what condition are engine management components .

 

For comparison i had LPG on mine for a few years , and it was nice and smooth while running on LPG no kangarooing/juddering/shaking on-off the throttle .

So , mainly it's the injection side that is to blame not as much the ignition .  

 

Not sure if i would trust someone set it up for me (unless they're well experienced working on Jetronic) , as they'll likely just adjust it up the book figures .. which may not be ideal .

 

I managed to adjust mine where it's down to minimal "kangarooing/juddering/shaking" , but after quite a while of test-try-tweaking .

Like i mentioned above - you need it a little bit on the rich side of mixture .. for making it less "kangarooing/juddering/shaking" @ low/mid range .

"Superchips" ECU mod (which is really just an two potentiomeners installed in the ECU) helps , as then you can tweak the injection pulse .. that along with properly adjusting the AFM , TB , and dizzy (test/clean the injectors as well) will make it as smooth as Jetronic can be . But takes time , patience and some tools .

 

D

Edited February 12, 2021 by DamirGTI

[Thijs_Rallye 87 4 Cars]

7 hours ago, Adamstanford said:

Still pure jerky at pulling off rpm. All gears. Even a small pothole can send it into a frenzy, the throttle is way too responsive. 

Have you checked all the items in my post above? link to the haynes: http://pdfstream.manualsonline.com/7/7f118b27-a3f1-4ff8-9629-65e8f8fb1488.pdf

 

Start with the basics, check and set valve clearance, check the amount of vacuum at the take off pipe as per picture here below, check iginition advance / vacuum advance and check if the centrifugal advance is still working the way it should. All this will make all the difference. And what Damir said as well, if there is a lot of play in the engine mounts this will amplify the jerky-ness.

 

Like I said before, they were never buttery smooth but if you omit one piece of the equation they certainly don't get better ;).

 

Edited February 12, 2021 by Thijs_Rallye

[PhilNW 44]

4 hours ago, 309SRiguy said:

Are your engine mounts in good condition? A worn out bottom mount can allow a lot of engine movement when moving on/off or off/on the accelerator. It can result in transmission snatch that feels quite violent at times.

Have a look at the drive shafts and intermediate bearing as well. 

Edited February 12, 2021 by PhilNW

[Adamstanford 3]

3 hours ago, PhilNW said:

Have a look at the drive shafts and intermediate bearing as well. 

I'll look at the bits you all mentioned, shafts/ bearing and bottom mount all new, I've just put a new gearbox in

[PhilNW 44]

2 hours ago, Adamstanford said:

I'll look at the bits you all mentioned, shafts/ bearing and bottom mount all new, I've just put a new gearbox in

Have you put on stands (and chocked) and run it in all the gears to see what happens when not under load/being driven? 

 

"Even a small pothole can send it into a frenzy" bit intrigued by this statement can you explain further? 

Edited February 12, 2021 by PhilNW

[DamirGTI 342]

There seems to be some options making std. Jetronic better performing on-off the throttle .. but needs experimenting .

 

One , using Nippon Denso AFM from Mazda/Toyota/Kia (essentially copy of the Bosch AFM's) .. using it as an base/body and fitting inside of it the old Bosch potentiometer plate and wiring connector .. as these seem to be better made and even flow more that Bosch unit , in order to eliminate that jerky on-off throttle transition of a Bosch unit .

Having had Mazda back in the 90's with such Nippon Denso AFM , and driving some other too , they where nice and smooth on-off the throttle .. so might be worth a try .

 

Another , gutting the stock Bosch AFM removing potentiometer plate , and instead fitting digital TPS inside . This i've done on one of my spare AFM's , but haven't yet tried test run it .. Anyhow , there's a fair few of people who did it and all of them seemed happy with that mod , they reported smooth on-off throttle transition and even slightly improved fuel economy .

 

D

[Adamstanford 3]

5 hours ago, PhilNW said:

Have you put on stands (and chocked) and run it in all the gears to see what happens when not under load/being driven? 

 

"Even a small pothole can send it into a frenzy" bit intrigued by this statement can you explain further? 

Like a small imperfection in the road, especially going up any sort of hill will move the car enough to make your foot move a cm or so which then starts the heavy jerking! Each time it jerks back into your foot making it do it harder. Only way to stop it is either floor it or press the clutch and try again. 

[Adamstanford 3]

4 hours ago, DamirGTI said:

There seems to be some options making std. Jetronic better performing on-off the throttle .. but needs experimenting .

 

One , using Nippon Denso AFM from Mazda/Toyota/Kia (essentially copy of the Bosch AFM's) .. using it as an base/body and fitting inside of it the old Bosch potentiometer plate and wiring connector .. as these seem to be better made and even flow more that Bosch unit , in order to eliminate that jerky on-off throttle transition of a Bosch unit .

Having had Mazda back in the 90's with such Nippon Denso AFM , and driving some other too , they where nice and smooth on-off the throttle .. so might be worth a try .

 

Another , gutting the stock Bosch AFM removing potentiometer plate , and instead fitting digital TPS inside . This i've done on one of my spare AFM's , but haven't yet tried test run it .. Anyhow , there's a fair few of people who did it and all of them seemed happy with that mod , they reported smooth on-off throttle transition and even slightly improved fuel economy .

 

D

These sound like awesome options but probably beyond the scope of my ability. 

[PhilNW 44]

Based on your comments: -

• as you release the clutch it'll start kangarooing and jerking as if you're stabbing the throttle. 
• it drives and idles perfect all the rest of the time
• So to be clear, it's jerky as hell at part throttle, any speed really. WOT is fine and idle is good also
• Like a small imperfection in the road, especially going up any sort of hill will move the car enough to make your foot move a cm or so which then starts the heavy jerking! Each time it jerks back into your foot making it do it harder. Only way to stop it is either floor it or press the clutch and try again. 
• I've just put a new gearbox in

What was it like before you put a new gearbox in?

Not clear from the above but have you changed the AFM?

 

I would be looking at the security of the engine/gearbox (hopefully not the clutch) and any play in the mountings gearbox/engine bolts, driveshafts etc

 

Sound like the engine is "floating about" which disappears when using full throttle (any slack would be taken up). but would not be apparent when idling

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