I have 2002 S80 T6 and i a have a few problems with the engine. The idle is sometimes good but usually the RPM is moving up and down a little. Sometimes the RPM drops so low the engine stops running. This also happens if i push hard on the throttle and release it while im in "P" or "N" or while driving and after a release the throttle i break hard. We cleaned every sensor, every valve, the throttle body, i bought new sparkplugs, new fuel pump, O2 sensor, checked the timing belt but the issue is still present. I could really use some help