I have a 99' 528i E39. When i start it up it has a rough idle to it. It will run fine then 'bog' down the rpm's abit then till go back to fine the longer it goes the harder the 'bog' downs are. After about 10 mins~ the car will shut itsself off on the last bog down. I can then just restart it. There is also a hissing sound from the drivers side of the engine i cant place my finger on, im thinking these 2 issues might be related. Ive checked all the fluids and they are ok.
Please help if you can.
-Branden