I have a 2006 Volvo XC90 V8 AWD with the 6 speed automatic transmission and I have 200,000 km on the odometer.

I have the following problem. When the car is stopped and in gear, it is trying to launch forward (or backward in reverse). It takes a lot of effort in pushing the brakes to keep the car from moving when I'm standing at a red light. No engine fault codes. The engine would sometimes halt at the light or when putting it into "D". When I put the car from "D" or "R" into Neutral or Park, the RPM jumps up to about 1200-1500 as the there is no more load. The RPM settles in a few seconds. There is no rough idle.

Has anyone had this experience? What could cause this?

I had this car for about a year. In the first 3-6 months we had the transmission acting weird. Sometimes it wasn't sure what gear to put the car in, often switching up and down and sometimes I experienced hard gear changes on the downshift. On a few occasions it would just put the car into neutral. I considered this a problem with the "learning" TCM these transmissions have. I had a full software upgrade at the dealer, including TCM upgrade and the TCM was also reset. This made the problems worse at first, but as expected the problem went away slowly - it took about 3 months for this to completely go away. No more problems switching gears, and it has been about 6 months now.

I had a fuel rail pressure sensor that I delayed changing for a few months (engine light was on). While running with the faulty pressure sensor the current problem of launching came about. Changing the sensor did not make the engine light go away. I took it to my mechanic who had a lot of work on it. At this time the only fault code was P0506. We started to look for vacuum leaks. Changed a bunch of stuff:
- vacuum switch for the power assist
- manifold gaskets
- PCV valve was changed (this was actually faulty)
None of these made the problem of launching go away and the engine light stayed on.
At this point we started to change our driving habit. Whenever we stopped, we put the car into Neutral. Soon the check engine light went away, but the problem still persists.

The problem is there constantly. I can only think of a couple of instances when the problem went away. However, when we gave it some gas at the sight of the green light, there was a slight slip of the wheels and the problem came back.

There are some thoughts on what to look at next, but the price tag has been on the climb for a while. I hope to get some ideas on what the issue could be before, I share what my mechanic plans to do.

All help is appreciated.