Whisper

Started this morning, about halfway through a short drive, the car suddenly starts shuddering in the rear and sounding like a truck... but only when taking off from idle, or when rpm are low.

Funny thing is, I don't feel any slippage.

Anyone have any ideas?

JohnKoaWood

CV joint bolts?

N/A or turbo?
Year?
Mileage?

Presure plate going bad causes clutch slippage, usualy not shuddering unless some other trauma has ensued.. My first thought is CV joint bolts... hit em with a torque wrench....

Whisper

86, N/A, no trauma, 165k miles.

Thing sounds like a truck taking off, and shudders a lot, then suddenly smooths out and acts normal.

Whisper

Now that you've tuned me into it, the sound and vibration does seem to come a bit more from the left.

But what do you mean by the CV joint "bolts" being the culprit? It's not the joint itself grinding (grease leak) or otherwise misbehaving?

What can go wrong with the bolts?

KuHL 951

They can come off easier than Britney Spears pants. They will make a knocking sound. Hopefully your ring and pinion isn't going out on you. A bad CV can make some awful sounds and they are easy to check on the car.

Whisper

Hopefully the results are less horrifying.

Yeah, "awful sounds" sounds like it. Fortunately, worst case is "replace the whole CV axle", and that's pretty cheap to do.

I was just concerned at first that it might be the clutch disc or plate, since it seemed rpm dependent.

V2Rocket

Did you get the new bleeder screw in?

I don't think I'll be back in Riverside this week but I will check it out as soon as I can.

Check to see if that big muffler is loose at all, that might be the noise problem.

Whisper

Nah, it's not the muffler. This was a shudder, not a rattle.

And it started very suddenly. Just one jolt, and there it was. No gradually increasing clicking sounds.

Would that mean it was one or more of the bolts?

Whisper

Okay, was I ever wrong.

Took it for another shakedown today... ran fine until it had been going a while. Then it suddenly started sounding like a truck and chugging even on idle, with a lot of shudder from the muffler on takeoff and under acceleration.

No shudder while coasting, even on corners, so CVs are fine.

Thing is, every once in a while it would shift back to smooth for a second or two.

I think it has something to do with the new idle valve. Defective part, or possibly getting bad data from AFM?

Next step would be to pull the idle valve's connection from the AFM when it's warm and doing its thing. Any other suggestions?

DarylJ

Why would the ISV have anything to do with shuddering under acceleration? Maybe I'm not understanding what you are saying.

Whisper

Yes, I think you misunderstood.

Every time I step on the gas, it chugs so bad it shudders. I think if that valve is defective, I may be waaaaay rich.

DarylJ

You think that the "idle valve" you mentioned above, if broken, will make you run rich? What exact valve are you talking about? Surely not the ISV.

It sounds like an AFM issue.