05 Volvo XC90 T5 with unstable eng rev.

[minwoo]

Hi, all
I have 2005 XC90 with T5 and issue has been going on for about 6 month.
As soon as I moved out to California temperature reached around 110 during the summer.
when the outside temperature rises, engine revs. up and down with steady rpm.
with AC on it gets worsens.
have no issue with driving the car, but when the car is parked or stopped I hear engine rev up and down with steady rpm.
I took it to the dealer and they found (Vehicle seems to Surge)
ECM120
S12 Minor Engine Repair
contaminated throttle body Recc.
price to fix $350.
any one had a same experience?