Low-Speed Surging or Rocking

[Lipper22]

I am a newbie with a frustrating question. I purchased a 2001 XC70 with 55K miles. At very low speeds (between 1 to 2 MPH) the car rocks slightly or surges, both accelerating and slowing. This is not very noticeable except when you are sitting in stop and go traffic. I took the car to the dealer who told me that the transmission was not showing any codes but that this might indicate a problem with the "sun-gear". The dealer upgraded the transmission software for $150 and this did not help the problem. Another mechanic told me that alot of Volvos are know to do this and that it is just an operating characteristic of the car. Has anyone else experienced this problem?

[Art]

Welcome to the site Lipper22! :)

It almost sounds like an issue with the ETM. Carbon deposits can build up in the bore if your car is driven short distances frequently. The residue can then cause the idle speed to become uneven particularly when the air conditioning is cycling. If this is the case, then a cleaning of the throttle module might be all that’s required.

[mrmay]

Lipper22,

I have an '01 xc70 with 42k on the odometer. I have noticed a similar symptom in my car, though usually when I am at a complete stop and it seems to be worse when the car is cold.

I took mine in to the dealer under warranty for this issue about a year ago. I don't remember exactly what the tech said, but I seem to remember something about a valve. I wasn't paying close attention because it was on Volvo's tab. Anyway, the fix seemed to work until just recently. It is once again acting in a similar manner.

I'm sorry I can't be of more assistance now, but I do have an appointment this Wednesday with the dealer for this and other warranty issues. I will post here when I have results from my dealer.

mrmray

[Lipper22]

Thanks for the reply. Actually this seems to be worse when the car is warm, not cold.

[Lipper22]

The ETM theory is something I hadn't thought of. However, the problem doesn't seem to be impacted by usage of the A/c either way. Thanks for the thought though.

[TrueBlue]

From all the posts here looks like a case of the "dreaded Throttle Body".

Gets gummed up with your cheap Gas.

The TB can be cleaned, or replaced depends on whether you think it's worth the labour.