This appears to be a common problem with the S70/V70/C70 and mine has started doing the same. From the threads I have found here and elsewhere it appears to require replacement of the Electronic Throttle Control module.
I've just been in touch with BBA-ReMan in the UK and they are looking for any information anyone has on the symptoms / frequency of occurrence of this problem (it seems from the posts that this is a reasonably common occurence).
Their website is http://www.bba-reman.com and if there are sufficient enquiries from Volvo owners they may consider producing rebuilt units. Whilst this doesn't particularly help me for the moment it is definitely worth calling them if yours fails in case they have started rebuilding these.

In the interim, if you have had a replacement ETS throttle module, can you please post a reply stating car model, year and mileage/year at time of replacement? I can then feed this back to hopefully assist them in determining the viability of gearing up for this work.

Thanks,

Alastair

I just had my ETS module replaced on April 21, 2004 on my 2000 Volvo S70. I noticed the ETS problem a couple of months ago. During stop and go traffic, it would blinked very quickly. Until this Tuesday, it came on and the car accelerate sluggishly so I replaced it on Wednesday. Today as I was driving in stop and go traffic, I noticed the ETS light blink once, is this normal? or there may be other problems with my car?

We are in the process of replacing the Throttle control today! The ETS light came on last week and we have been afraid to drive it. The dealership told us we could drive it until the car stalled. I don't feel comfortable knowing my car could stall at any point in time, especially when I'm driving my family around.

We purchased the extended warranty and it does not cover this. Our car has $70,000 miles on it. We have been quoted $800 to repair it. We are looking at trading our car in after this. We have had more problems with our volvo than we ever did with our Honda which we sold with 100,000 miles and not one repair problem.