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The DME is the fuel injection/ignition control computer and idle speed is one of the many functions it controls.

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Someone suggested replacing the DME relay, as they sometimes get sticky or internal solder points can cause bad connections. Does anyone know where the DME relay is located on the 2004 Cayenne S? I have inspected all the grounds around the DME and around the battery and the frame, they all are solid and free of corrosion. My Durametric software indicates it is idling @ 580 RPM, is that the correct idle RPM under load?

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Porsche tech said it feels like a bad engine mount, because the RPMs are not dipping. I have confirmed that with my Durametric software. He put it up on the lift and found a broken front differential mount. (There are 3) The torsion bar on one of the engine banks, which has rubber bushings on both ends, was also shot. I started out by replacing the torsion mount, but that did not resolve the problem. I am convinced we're on the right track, though. Does anyone have detailed instructions on how to replace the engine mounts? I might change those while I'm doing the front differential mounts.

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So nobody wants to try cleaning the throttle body to see if that helps the problem??

In one of my previous posts, I mentioned having the same problem.

I've followed vivicary's advise and had the throttle body cleaned at the dealer a few months ago.

Sub Idle, disappeared. :thankyou:

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Motor mounts. I just had mine replaced on 04 Cayenne S. No more idle shudder when coming to complete stop. Hydraulic mounts had settled 1 inch, without leaks. It's like having a new car. What a difference!!

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The engine mounts were about $150 each and the transmission mount was bout $40. The labor is 12.5 hours because the engine and subframe have to be dropped. The independent shop I used charges $95 an hour and they did do a great job. It wound up costing me around $1300 total. Definitely the best investment I/ve made. My complaint was the shudder while comming to a complete stop, but I had not even noticed the constant hum and resonance in the cabin until I got the mounts replaced. Now its like whn it was new. From the moment you start it up, it is so smooth and quiet that you can't even tell the engine is running.

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Reaction1,

Good news about the engine mounts.

Did the tech explain how the engine mounts were affecting the engine idle?

Edited by bigbuzuki

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It does not affect the idle; it only feels like it does. I had hooked up my Durametric diagnostic software and confirmed that the idle was not dipping during this shudder. Eventually, you'll feel it slightly when idling and you put it in Drive or go from Neutral to R or D, or put on you high beams, etc. Anytime the engine is under load you will feel this reverberations. It is in fact a resonating sound felt throughout the cabin due to the collapse of the hydro-mounts. It only happens under load and therefore appears to be affecting the RPMs, but it is not. Prior to replacing the mounts, I had methodically eliminated other possibities until I heard a mechanic say that they change a lot of Mercedes Benz hydro-mounts after customers complain that the vehicle isn't as quiet as before. It starts becoming noticeable after about 50,000 miles. In addition, I read that the old Porsche 928-S had hydro-mounts (and a V-8) and were known to have issues with these mounts. The independent mechanic that replaced the mounts on my Cayenne said that he had just replaced engine mounts on a fairly new Range Rover, also with the same type of mounts. The key is that thse mounts don't separate, as the traditional ones do, they just compress so that the engine is resting right up against the bracket with only a minimal amount of compressed rubber sandwiched in between. Diagnosing them is difficult and replacing them is a complicated job.

Reaction1,

Good news about the engine mounts.

Did the tech explain how the engine mounts were affecting the engine idle?

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Hydraulic motor mounts on BMW V8s are incredibly problematic as well. Aside from vibration, you can see the position of the engine lower when they fail, not to mention oil all over the place. On my X5, the engine was sitting about 1.5" - 2" lower than normal when I bought the car. Anyone used to working on one would immediately notice that the engine was sitting low. While a big job on the BMW, at least the engine stays in; although the A/C compressor must come out.

If you suspect a motor mount failure, I would look carefully at the engine position as compared to another Cayenne.

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Manual says engine mount replacement can be done without engine removal on the S.

Engine needs to come out for the turbo though.

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