Surge/oscillation

[wardsc]

Hello everyone; looking for some expertise, which seems to be abundant on this site. We have a 2001 XC with 62k. It has been running fine, with no hiccups since we purchased it last Oct. Of late however, on the highway at any steady speed we are starting to feel a slight, very subtle surge or oscillation. The engine is normal, with no rpm drop or change, and there is no abnormal sound associated. The car had it's 60k early(according to the dealer-no way to completely check). The tires are 6k old(all 4 replaced at same time), and rotated at the initial 1k of life, as I was trying to correct a slight vibration that is still felt at highway speeds also(very similar to the other postings on the forum. I can't figure out if it is drivetrain related, or fuel starvation(Filter?). Has anyone out there had this anomaly, and does anybody have a suggestion? Thanks in advance...

[geo]

Hi, is this in cruise, or are you holding the throttle down yourself?

[wardsc]

Holding the throttle down, at steady speed.

[wardsc]

Starting to become more noticeable-it seems to stutter/slightly hesitate when softly holding/pushing down the throttle to maintain hwy speed....anybody have any ideas?

[geo]

I have a D5 diesel xc70,
There is surge on cruise at low speed.
There there is a form of surge in cruise at 60 m/h
I tried yesterday and cold within 2 miles of start up, urban 30m/h contant throttle there is also surge noticed, about 75r/m revs variation.
This goes away when hot.
no ideas as to cause at the moment other than an over active or under re-active set of sensors and servos.

[wardsc]

New update-the car is now back at the dealership after trying the new software download...the problem continues to get worse...now a distinct stutter/hesitation while maintaining any speed...will be trying new throttle body next....not convinced this is the problem, but I'm willing to try anything at this point...anybody??? Thanks GEO for the input....

[Shoop Dog]

Not sure if you have solved your surging problem yet but I just had my 2001 XC repaired yesterday for that same problem. It had recently had its 60K service as well as having the transmission replaced earlier this year so the dealer started the diagnosis there but after spending over 1 day searching for the problem and on the phone with the Volvo service gurus, they finally tracked it down to carbon-buildup on the throttle body. They wanted to replace it under warranty but had to go through a cleaning & testing cycle in order to satisfy the warranty rules. The cleaning solved much of the problem but the new throttle body has totally eliminated the surging.

Jim

[wardsc]

You are right-my problem was in the Throttle Body, but my dealer did not tell me anything about a warranty....I paid just under $900 for the job, but it is now running perfectly....

[1Lieutenant]

Hi all,

I am puzzled by the diagnosis of carbon buildup in the throttle body. I may be completely wrong (won;'t be the first or last time) but doesn't the throttle body just regulate the amount of air that is let into the intake manifold? This is a port injection engine (injectors in the intake manifold near the block and intake valve) so no fuel goes near the throttle body. Where does the carbon come from?

Has anyone tried Techron additive. This is excellent for removal of carbon deposits on intake valves and injector nozzles. My uneducated guess is that carbon deposits in these areas could account for surge and oscillation (carbon acts like a sponge absorbing the fuel and leaning out the mixture. It also affects fuel injector spray pattern)

Steve

[littlewaywelt]

Is this problem related to upshift flares?

I really think Volvo should have taken care of my 2-3 upshift flare (which showed up and was reported in the warranty period) via replacing the throttle body valve which they refused to do, practically accusing me of making it up or imagining it. I’m wondering if this new oscillation is a subsequent and related problem to that. Are the throttle body valves from early on that bad? Has anyone who has the oscillation also had the upshift flare?
The thought of dropping another 1000 bucks into this car within two weeks sickens me.

[tmcphail]

My 2002 V70XC developed the 'upshift flare' from 2nd to 3rd early on (under 5K). Dealer installed a 'software patch' that took care of it. Now at 40K my car just developed the surging/oscillation. It only occurs under acceleration though. Normal driving is fine. First noticed it when towing a small motorcycle trailer up a hill and surging was much more noticeable. Thought it might be turbo related. I'll definitely be calling my dealer to have this checked out. I thought it was my imagination!

[taylorjb]

My 50k 02 XC70 started "oscillating" on drives on the interstate in the mountains, and now it is doing it on flat interstate. It's a small pulsing, of about 200 rpm, when the car is going > 65mph.

Having looked through the threads, it seems the fixes could be:

Fuel additive
Higher octance fuel (on occasion)
Clean the throttle
New throttle

Other thoughts/suggestions?

PS. Besides a couple of quirks like this one, I have to say these cars are smart and nice. We drive in all kinds of bad Rocky Mountain weather, and just completed a very comfortable 5,000 mile XC drive...that I wouldn't repeat in any other car.