Surging accelerator

[alcraig]

My 2001 XC 70 surges a little bit even when my right foot isn't moving. Shows up mostly on uphills at moderate speed in 3rd or 4th gear. Today, with the window down, I could hear whining pitch going up and down in frequency with the surge. Seems to also happen when on cruise control, at 110 kph going up hill.
I'm thinking its being controlled by the ECU and either the actuator on the pedal is drifting, or the throttle body needs cleaning.
Thoughts?

Ta
Al Craig

[Astro14]

I think they all do that.... Slight uphill, 4th gear, light throttle, right? Both my cars "hunt" as the TC locks and unlocks. So, I select a gear manually...

[hoonk]

My 2001 surges a little bit even when my right foot isn't moving.
or the throttle body needs cleaning.


2001 was the last year the Magneti Marelli throttle was used. They are a known failure point. Cleaning the throttle body is always a good first step - but there may be a replacement throttle module in the near future for you. Xemodex and others offer reman units - at least in my part of the world -

[Antherzoll]

Could be an issue with boost control. If the TCV is original I'd replace it.

[alcraig]

Not sure if the TCV has ever been replaced. Will look into it. Also did some searching and found suggestions for replacing the vacuum lines as well. And then after all that, re-setting (adapting) the ECM using the 3rd gear - 3 accelerations technique as described here.

http://www.volvoxc.com/forums/showthread.php?25164-Turbo-Problem-Fixed!

Not sure if the TCV has ever been replaced. Will look into it. Also did some searching and found suggestions for replacing the vacuum lines as well. And then after all that, re-setting (adapting) the ECM using the 3rd gear - 3 accelerations technique as described here.

Will shorting the battery leads re-set the ECM such that I would also have to do transmission and braking adaption?

Ta

Al

[Antherzoll]

Will shorting the battery leads re-set the ECM such that I would also have to do transmission and braking adaption?

Ta

Al

Shorting the battery leads will not affect anything but engine parameters, just remove the negative and touch it to the body, hit the brak pedal a few times then reconnect with the key in pos II (I never follow that last instruction and I've been fine) . Just drive easy for the first few miles and increase load gradually.

[JRL]

Actually not quite true
Even Volvo mechanics sometimes do a complete dump
They tie/clamp the positive and negative leads together for 30 minutes, pretty well clears everything out.

Your problem is NOT your TCV
ETM and/or MAF, usually replacing both will fix the problem

[2002V70XC]

isn't it because of the AWD engaging? I did have that kind of feeling going uphill on the highway but I didn't notice any noise. It felt like the AWD was engaging a little bit harsh! It got much improved after I changed the AWD fluid (front and rear).