I have a 11’ E82 135 6spd. N55. After warming the car up and driving for a little while. I will come to stop light. Rail pressure will drop down to normal approx 724psi. Then after about 5-10 seconds of idling at the light the rail pressure will rise to 12-1300psi. If I tap the gas pedal it will drop back down to normal. Or if I just wait it will also drop to normal. But then rise again to 12-1300 after a few seconds. Any ideas what could be causing it. Car runs just fine everywhere else. TIA