The problem started almost two years ago.
The car was starting and running fine but when was going to compete stop the RPM was dropping to 500-600 RPM just for a second and will go back to normal . It never stall. Finally I decided to clean the throttle body two weeks ago.
I disassembled it and cleaned it. The above problem disappears.
Two days ago started a different problem. The car is starting fine. The engine is idling just fine. But when try to accelerate it won't. In parking position I will push the pedal all the way down and noting change. It won't accelerate more then 1000-1200 RPM.
If I drive it will move with like 10 Mph. Pressing the acceleration pedal up and down and the engine will suddenly revs and become normal.
I'm not really sure if there is some relation between this two problems.
Yesterday I cleaned the MAF sensor and that didn't resolve the problem.
Any suggestions ?

 

What year and sub-model is your S70? Turbo or NA version? There are some fairly major differences under the hood between the '98 models and the '99/2000 models.

...Lee

 

In addition to Lee's questions, is your CEL (ck engine light) on? If so, have you read the codes?

 

It is a 2000 Volvo S70- nonturbo. 207k miles on it.
The chech engine light is off.

 

OK, does your CEL work? How about your ETS light?

These lights are tested during the "bulb test"; i.e. they should come on during engine cranking.

Any other background info like has the ETM ever been serviced or replaced? What exactly was involved in "cleaning the throttle body"? Etc...

 

All lights are working fine including the check engine light.
I checked for faulty codes. Didn't show any existing code but there was stored code P1603. The ETM is with yellow sticker on it. That means that in some point it has been changed. The number on the bottom is 02W111303. I saw somewhere that this is the date of production. Also in 2009 software update have been done on it.
For the cleaning I disassembled the ETM and cleaned all build up inside of it using CRC throttle body cleaner. I wait until is dry and assembled back.

 

Sounds like you covered the basics pretty well. Assume you've ckd for vacuum leaks?

According to here:
P1603 = EEPROM Malfunction
which I would assume is referring to an internal part in ECU but someone at the dealer could tell you for sure what it means (P1xxx codes are manufacturer specific).

And that may or may not be related to your current issue. Ultimately you may need an ETM; xemodex is a better-than replacement. They've got a pdf diag flowchart for debugging ETM; unfortunately i can't find where they've posted it on their website. You can contact them and ask for it.