So, twice in the past few weeks, I have pulled up at stop lights and instead of RPMs continuing down while I slow down, the car acts as if I just floored the gas pedal. So I push very hard on the (new) brakes and it stops. . .barely. It's wanting to just take off. The RPMs are around 2500 in these moments. If I try to put the wagon in Park or Neutral, RPMs redline. Put it back in drive and keep my foot heavy on the brake, RPMs still around 2500. When green light comes on, I leave a lot of space between my wagon and the car in front of me in case my car takes off like a rocket (or as fast as a 940 can go). When I'm in drive at 2500 RPMs while stopped and ready to go, I take my foot off the brake and the wagon's RPMs drop to 700 and the wagon acts totally normal.
Anyone ever heard of anything like this? My old Volvo mechanic retired last year and I'm afraid diagnostics alone at my new shop are going to be $$$. Maybe time to retire the car.
Check engine light is not on. About 235k miles.
Thanks,
Nick

 

Your idle motor/aux air valve/IAC whatever you want to call it might be sticking -

First - have someone depress the gas pedal while you watch the linkage (engine off) - the throttle cable should open and close the throttle plate - and the kickdown cable should be pulled out and retract smoothly - make sure all that is happening as it is supposed to and nothing is preventing the throtle plate from closing.

If the idle motor is sticking - cleaning might help, or if the base idle is set (properly) high enough - The car should idle when warm without any air going thru the idle motor. (clean the throttle housing, set the basic idle and throttle switch. The throttle switch tells the idle motor to try to keep the idle in the proper place) You can simply clamp off one of the hoses to the idle motor to see if the idle motor is causing the problem. (I understand the idle motor hoses might be not so soft anymore as to allow a clamp off function withour cracking/breaking them)