gruffalo

Hi, all. My 928 runs strong as ever, but has gradually developed a problem.

When cruising at low speeds in low gears, the ride si somewhat jerky. When I go slightly on/off the throttle, some sort of pulsation takes place through the drivetrain. It is not misfiring or anything, it just jolts and jumps (my English fails to describe it properly) while it accelerates. The same thing when I go off the pedal and coast.

On half to full throttle it accelerates smoothly.

I've planned to replace ignition parts an injectors. But could bad motor mounts cause this?

The jerking/pulsation is at 1-2 Hz, so not a vibration... and no misfire. It just goes uh-uh-uh-uhhhh-bwhaaaa. I think you see what I mean.

Please advice!
MM

Mike Frye

What is this 'part throttle' you speak of?

gruffalo

throttle partly open. Like in "pedal 20% down"

Jadz928

My '84 just started doing the same thing. I think it's related to the clutch. That is all I know at this point.

Mike Frye

I'm sorry, I was kidding. Part throttle isn't something I'm familiar with.

Does it feel like a clutch issue? Is it in any particular gear or in all of them? Also in reverse? (Edit: I see you said low gears, is that because you don't use the same RPM range in the higher gears or maybe you just don't notice it?)

Can you get under the car and pull the plug in the lower bell housing and check the clutch wear amount (I think there are different rules for different MYs, I'm not sure where yours would have to be in order to show wear).

Have you gotten any moisture on your flywheel by cleaning your engine and spraying it down into the top of the bell housing? I've read about people having a 'juddering' when going into gear and at least one guy whose clutch froze (Rusted) to the flywheel when he got some water down in the hole where the top of the release arm goes on the ball.

I've noticed some weird clutch action after a rain when (I assume) some water or moisture has gotten on the flywheel or clutches. Usually only when starting out, presumably it gets cleaned off after a few gear changes.

toofast928

Check for vacuum leak.
Also a coolant sensor could cause a "hitching" effect.

9two8

I occasionaly experience these symptoms (Not always) when it does it I slip the clutch a little and it goes away, I realise this is,nt a cure however, and thought untill I find a good remedy it,ll have to be something to put up with.

Over this last winter I,ve replaced all vacuum lines resulting in a very smooth and balanced idle..., won,t know for sure if it,s helped the jerkiness untill she,s on the road (fingers crossed)

Ken
80 928 S
5 Speed

UK

Ted928

I have a similar issue but it related to the engine management system, not the drive train. The engine speed is not smooth at off throttle and slight throttle. If I am moving slowly in gear up a slight incline (~1100 rpm) trying to move with traffic, I can't give it a little throttle or it will jerk (accelerate) causing my foot to come off the throttle, causing decelation, causing my foot to fit the gas.....
I have to keep my foot clear and I usually clutch. It has done this for years. Is this similar to your problem????

My TPS does click when I open the throttle plate but I have not checked it carefully. The WSM says that the click must occur within 1 degree of throttle opening. Not sure how much 1 degree is but that sounds to me like set the switch as tight as you can so that the slightest plate motion opens the switch.

gruffalo

Exactly identical!

In the wost cases I get PIO as you describe.

In my case this has come gradually over the last year or so. The clutch is not slipping. I still hope a tune up with new ignition components and injectors will cure it. But I loath the mm's, so if no-one thinks thay are to blame, they'll have to do for now.

gruffalo

Well, me neither, but when it's cold I try to be gentle...

I should post a picture of my rear tires compared to the fronts, and I would instantly be off the hook on this one...

Ted928

I recently replaced my motor mounts. Did not change the partial throttle issue we described but It drastically improved the ride. I had no idea how bad it had gotten. Feels like a new car - well worth the effort. I have a car lift so the work was not bad.

I freshened my intake a couple of years ago - including new injectors. Repaired some oil and vacuum leaks but did not change the partial throttle problem. I checked to make sure the idle switch was working but I did not check to see if it was adjusted properly.

Lizard928

the jerkyness you describe is either caused by 1 of 2 things, either your rpms are too low and you are lugging the engine, or your AFR are too lean in that rpm/load band.

andy-gts

I had similar issues and it turned out to be the TPS and a plugged fuel filter. Probably the fuel filter was the real culprit

R.Pires

Hi all,

I guess I have an identical problem!
It's irritating!
Look here: http://www.nichols.nu/tip384.htm
I've ordered new spark plugs, plug wires, distributor cap and rotor, new coil.
I think the ones in the car are original, they look good but.... they have 26 years old!
Let's see what happens when all that is replaced!

Regards

Ricardo Pires
83S Euro 5spd

928ntslow

sounds like a fuel delivery issue