"Bucking" at highway speed?

[haasonsock]

I am coming to my wits end with this problem. I purchased my 1998 volvo V70 XC in August 2001 with 17,000 miles.   I have been experiencing occasional "bucking," (for lack of a better description) as if there is a miss in the engine. I notice it mostly at speeds of 50-75 mph. My dealer cannot find anything, and of course, since it is not occuring at all times, they haven't felt this happen. They say no codes come up on the diagnostics.  Does this sound familiar to anyone, and do you have any input?  

[sjcoffey]

I had the same problems on my 98 XC.  It was corrected after the dealer updated the ECU with the latest software.  The problem is referred to as the "skip and dip" on other forums.  I might still have the TSB number if you need it.

[srs]

I had a similar sounding problem on my 1998 which the dealar termed "Automatic transmission harsh lock-up engagement and disengagement" I could often reproduce it at the same speed range by coasting then lightly accelerating. The fix was a trans flush with an expensive fluid. My dealar comp'ed it because it took so long to figure out even though Volvo had a service bulletin on it but I recently read the bulletin and it was covered under warrenty. It was done Dec 2002 and I think I feel it returning. The bulletin has this info on it: Section 4 Group 43 No. 0029 Year 01 Month 05

[oddie]

I have to say I think I agree again with srs, since the speed is around torque converter lock up time it could very well be dirty trans fluid... You do have an automatic I'm assuming. Otherwise I would recommend fuel injector cleaner and possibly replacing the front o2 sensor. I would only do the o2 sensor if a decent technician recommends it however (tests yours for slow response).
Check your trans fluid by wiping the dip stick on a white napkin, first wipe will be awful looking due to debris stuck to the stick, second dip and wipe should be ruby red, little or no hint of brown. Have the trany power flushed if it is dirty. Still unsure? If you've gone 60k miles or more on the fluid its time for a flush, the trans will go so much further with this maintaince anyway that its not wasted money if it isn't the problem but it probably is.
Good luck!!
srs.... first the sway bar links, now this!! Are you a tech???

[RSD911]

I too had this bucking problem on my V70XC 1998. I noticed the previous owner had taken the car to the dealer at least half a dozen times complaining of this fault. They would do tune ups, trans flushes etc.....with no resolve.

Thanks to ALLDATA, I came across a TSB on this problem and had the tranny ECU flashed with new software, and the car has performed flawlessly for the past 3 years.

I can never figure out why the local Volvo dealer doesn't even know how to fix their own cars. I mean why should the consumer have to tell them what to do. Do they even read the TSB's that come across their desks?

Anyways, anyone having this issue with their V70 should get this ECU flash done.

RSD :cool:

[billandiris]

I too had this problem, as well had hard shifting. The new software was loaded and the tranny flushed and most symptoms have gone away. Having found this article, "An occasional problem on this vehicle is failure of the Electric Throttle Module (ETM). Carbon deposits must be cleaned from the ETM." I plan on going back to the dealer and have him check.

I describe the problem as pulsing of the throttle at fixed highway speeds with no visible drop in RPM.