968 Shudder on Acceleration

[flash968]

any oil leaks?

[Jamie '92 968]

Yes.
Many oil leaks, incl. rear main seal, oil pressure relief gasket, oil pan gasket, level sender gasket, oil cooler line o-ring...
Pete and I made a list, but I'll have to cross check it tonight to list them all.

[Robert Adams]

I'm going through similar frustrations.
A while back I had to replace a valve spring. That was about 30k ago. Had similar symptoms.

I recently started experiencing the same sputtering as you describe. 1st I went with a higher grade octane for a couple fill ups. Made a real difference for me....for a while at least. The combo of winter gas & ethanol mixes is I think starting to take it's toll, although I don't have any real testing of any sort to back this theory up. Anyway that seemed to help the situation.
Condition came back again, but stronger. This time we checked the plugs & wires etc. Since I was at about 30k with them I changed them all out. In the process found I had blown a plug in #1. So now we're checking mixture. Cleaned the MAF and I must admit I didn't get as much of a bang out of cleaning it as some here have...oh well.

just some thoughts. Good luck!

[flash968]

rear main - hmmm - i wonder if the clutch is actually slipping a bit under heavy load from oil

didn't actually think about fuel, but a 968 requires a MINIMUM of 90 measured ron+mon/2

[callmethewander]

Flash, I'd like to hear the joke about the 4 blind men and the elephant!

[flash968]

lol - ok - this is old

without knowing what it is, 4 blind me are walked up to an elephant and told to reach out and feel it and determine what it is

1 says "a tree" after grabbing a leg
another says "a rope" after grabbing the tail
another says "a snake" after grabbing the trunk
another says a wall, after putting his hands on the elephant's side

diagnosing things here is very often like that - we are all imagining what it might be based on what we "feel" when we touch the elephant, but we rarely have enough information to accurately diagnose the problem

[Jamie '92 968]

I plan to keep accumulating data on when it happens and when not to try to establish a pattern. Last night and today there was no sign of the dreaded "shudder".
My best guess at a pattern is that it may be more common when the weather is wet, or was wet the day before. I'll need more data to establish a pattern for sure.
I may also try to chart it by astrological sign. I believe my car was originally delivered in February, so is may be an Aquarius, or possibly Pisces.

I'm also going to replace the plugs, since it's been about 42K miles and 4 1/2 years, and they are cheap.

Flash, I guess the oil on the clutch theory is a possibility. Any suggestions for a conclusive diagnosis or remedy short of replacing the rear main seal (I was hoping to wait and do it with the clutch someday)?

Also, I thought the min octane was 93, which has been hard to find lately, and had been feeling uneasy about using 92. I also put a bottle of octane boost into the car when the shudder first appeared as a test, but to no effect.

Someday I'll again be able to aggressively hit the accelerator with a sense of excitement rather than dread...

[dapatch]

@both Jamie and Robert

I'll join the gang. My '93 968 CS has similar problems. Mileage, currently at 205.000 km is quite similar as well. My car has full Porsche service history but unfortunately I don’t have they invoices which show what work has been done. Could be that both clutch/DMF are still the original ones.
My car suffers from both shudder and shift problems (the latter only when cold).

[Jamie '92 968]

dapatch,
Are the characteristics of your "shudder" consistent with what I have described?
When does it happen?

(interesting but completely useless observation that those who measure distance in kilometers still refer to "mileage". Never thought about that before.)

[flash968]

no clue how to diagnose that one over the wire - best bet is to go back to pete

minimum is 95 RON, which crunches down to 90 here in the states though, because we measure by RON+MON/2 (also known as CLC or AKI)

however, to get maximum power, you need to run 98RON, which is 93 the way we do it - less than that and the timing gets advanced less, costing power

it's all in the owner's manual on page 112

[dapatch]

Jamie,

Yes the shudder is consistent with what you described. It occurs typically while accelerating with full throttle from 2000/3000 rpm. I’ve never experience the problem on higher speeds (200 km/h and up).
On some days I don’t notice the problem at all.

The type of the petrol has no effect on the car’s behavior. I’ve tried 95, 98 and 100 RON here in Europe.

[Jamie '92 968]

dapatch,
How long has your car been doing this?
Does it feel to you like the clutch is slipping, or that it is something happening with the engine?
Since my description of this elephant has not brought us to a conclusive diagnosis, can you add anything descriptive to help?

[dapatch]

I don’t know if I can describe the problem better then you did. It’s kinda hard. Today I did some experiments but unfortunately no shudder this time. What I did notice, while flooring the pedal in 6th gear at around 2000 RPM, is what felt like a slight slip of the clutch. At ~2200 RPM it was stable again.
I’ve heard a lot about dual mass flywheel problems in the first version of the 964. Somebody here who can describe the symptoms in that particular car? Probably they’re similar…

[dapatch]

If driven the car for no more than 1500 km (~1000 miles) since I first noticed the shudder.

[Jamie '92 968]

UPDATE:
The dreaded shudder is finally gone!
I had a chance to replace my spark plugs, and the problem just went away.
The car idles more smoothly now too.

Strange thing is that though the plugs were a bit overdue for a change (40K miles vs recommended change at 30K) they were in very bad shape.
Could this be due to the MAF sensor problem that was recently fixed, or is it an indication of something else I should look into?

Dapatch - when were your plugs last replaced?

[flash968]

plugs degrade performance gradually - things like oil fouling, rich running and such will accelerate that

even with everything perfect on my car, i can't get 10k out of my plugs before i notice a change, and since i want my car at 100% every time i get in it, i change them more frequently than they "need" to be changed - i also run the best performing plug i can get, which is currently the NGK iridium

same goes for rotor and cap

[Jamie '92 968]

Thanks Flash. I'm a happy guy again, now that my car is running well. I appreciate all of your help along the way.

I don't recall seeing rotor and cap as a maintenance item in the schedule (maybe I missed it).

What do you recommend?

[flash968]

no worries - happy to help

normally these things go for 25k miles or so before they start showing signs of cap or rotor wear, but i seem to burn through them faster - lol - could be just because i spend most of my time over 5k rpm

a symptom of a bad rotor or cap is an occasional miss at high rpms or more commonly an idle that isn't rock steady

pop the cap and take a look - if the contacts look scored on either the cap or rotor, replace them - they sell them here