What is the problem with My car?

[amigo]

My new c5 2.0 rhr 2009 has a problem that I hope some can answer me on what is defective ...

When I drive on the road and release the accelerator (eg caught up a car) and then press the accelerator agian no matter how gently I do, there is a jerk or notch a metal sound i can feel in the cabin. I sense it as if there is a little freeplay ect in a driveshaft or some Thing right before acceleration, but what is that? The clutch and flywheel have been changed 30000km ago so do not assume the fault is there.

[Dormouse]

how does the car behave in stop go traffic? is this problem apparent when you change up the gears?

[Peter.N.]

I assume this is a diesel? Intermittent throttle response is on many cars is associated with a worn throttle potentiometer, I have not heard of it on a C5 or experienced it with mine but that's the only thing I can thing of off hand. It could possibly that the engine is moving due to a worn rubber mount.

Peter

[amigo]

No its not When i change gear(not what i can feel) its only makes the jerk/clonk When i press the accelerator pedal after releasing the pedal not When i move My foot only When i use the accelerator pedal i got that 1 time until i release the pedal agian and so on.. So its like there is some freeplay in some linkage or maybe a defective mount i dont know .. Sorry My english hope you can understand it.

[amigo]

Its a diesel 2.0 rhr engine

[Dormouse]

your English is a million times better than our Danish. The throttle is not a direct cable - it operates a variable electrical resistance. The throttle position is "sensed" by the engine's ECU. This is more likely to feel like a hesitancy or flat spot rather than a jerk. It is still a possibility, though. Do you hear any noise and/or feel a clunk from under your feet?

[Gregor]

Hi.

Are you talking about delay in acceleration or a "clonk" noise produced? I had similar problem twice. First time it was worn holder at the back part of lower wheel arm (loud metal "dong" sound heard at beginning of harder breaking or acceleration). Next time it was worn engine mounts (clicking sound at same conditions). First issue happened at 230.000 km the second at 250.000.

BR G

[amigo]

Thanks alot.
I feel a little clunk, The clunk feel is more in the whole cabin not only under My feet

your English is a million times better than our Danish. Do you hear any noise and/or feel a clunk from under your feet?

[amigo]

Its not a delay in acceleration it is a clunk and yes its a metal sound and I start to think a worn mounts can be the problem. I can feel the clonk in the whole cabin

Hi.

Are you talking about delay in acceleration or a "clonk" noise produced? I had similar problem twice. First time it was worn holder at the back part of lower wheel arm (loud metal "dong" sound heard at beginning of harder breaking or acceleration). Next time it was worn engine mounts (clicking sound at same conditions). First issue happened at 230.000 km the second at 250.000.

BR G

[amigo]

But a funny part is the clunk only gets there When i release the accelerator pedal totally and start pressing agian not When i release.. Ect When i press a little on the accelerator pedal i get the clunk and than Ect pedal to the metal No clunk first When the accelerator pedal is released 100% and I start to press agian and so on.. Hope you understand

[Dormouse]

yes. pretty much anyway without being there in person. I think you still need to look at the engine / gearbox mounts / stabilisers first. When you coast the engine settles in it's mounts and when you apply power it then tries to twist in it's mountings but that does not explain why you don't get a clunk at other throttle levels. Next area to look at carefully is the lower suspension arms / anti roll bar links - this is less easy to isolate as the bushes may appear to be firm but the centres may have broken up - careful levering may reveal wear in the mountings and the bushes. Look carefully for any small area of bright shiny metal which would be where metal touches metal. After that I am at a loss for the moment. Have a look around the exhaust joints and mountings and look to see if any clearances are too small.

[Gregor]

But a funny part is the clunk only gets there When i release the accelerator pedal totally and start pressing agian not When i release.. Ect When i press a little on the accelerator pedal i get the clunk and than Ect pedal to the metal No clunk first When the accelerator pedal is released 100% and I start to press agian and so on.. Hope you understand

Hi.
What about when your vehicle is stationary? Is your C5 on "hydraulic" suspension?

Gregor

[thorter]

I am no expert on this, but I seem to remember that the throttle pedal can have two potentiometers or sensors, arranged so that the output laws track but intentionally different and unambiguous. The ECU then checks that the outputs correspond, so called coherence. If the coherence check fails, power and revs are severely restricted. So if one potentiometer is failing, coherence could briefly fail then work OK, and might cause uneven power delivery.

[Dormouse]

this one is a puzzle. The next thing I would look at is driveshafts all the way from the differential to the wheel hub and the brakes for secure fitting / play / wear. The fact that it does not happen under other throttle conditions is odd. Have you tried to make the noise/clunk happen by continuing accelerating / decelerating several times together?

[amigo]

Little update:

found one problem that i got play in the left outer sterring rod, replaced and that did help ALOT. the rest of the problem must be a gearbox mount somewhere, becouse i can see the stick is moving more than normal when i do accelaration and deaccelaration. so next is which mount can be bad one?