You were told wrong. Sure, cleaning the ETM could be some help but they all eventually fail, and when, is anyone's guess. The ETM is a closed unit that doesn't let any dirt in but fluids could seep in, so cleaning it with a high strength solvent is not such a good idea as you could potentially mess things up with the Mylar Potentiometer. Volvo sells a Throttle Body cleaner...I'd stick with that unless someone mentions something just as good here. It's the insides where the potentiometer is that is the major culprit for the ETM failure. The little metal fingers designed to send the electrical signal to the computer eventually rubs the carbon off of the mylar and there is no more signal and you go into limp mode and have to have the ETM replaced...and with the same defective unit...and for $1000....wow, what a scam. People who spent money to have their ETM's cleaned often complain of a failure shortly after...so cleaning is a not-for-sure method to straighten out bad idling and surging if that's what you already have. Some people who have had theirs cleaned have also reported that this seems to have solved their problem...at least for awhile. So, do what you think you should do.

Have you seen this?
http://www.volvoxc.com/forums/showthread.php?t=6026&page=22&pp=10

I would read up on this thing as much as you can and then keep up with what's going on. The national highway safety is now involved (with over 300 complaints) and may end up forcing Volvo to refund those who had to have this thing replaced as well as into a recall and redesign....as they are seeing this issue as more and more of a safety issue. Your ETM could go out anytime...in the middle of a busy interstate with a Semi barrelling down on your...your family with you, etc., etc.

Gosh, I sure do hope something is done for all the hundreds of thousands of Volvo owners out there that are having to or have dealt with this.

By the way, I researched this issue thoroughly and bought my '98 model Volvo this year, avoiding later model 70 series cars for the ETM issue alone. I hope that eventually my wife's '04 V70 doesn't have this problem.
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon