So I've had my E39 for two months now and I really love it--it's such a smooth and great drive. But to be honest: it loves the mechanic! Here is what's wrong with it now and I hope I can get some feedback to help me understand what's wrong with it because the mechanic has spent about 8hrs on it already and fixed one vacuum leak but the problem is still there.
For two months the engine was running fine but about 2 weeks ago the engine light came on. I took it to the mechanic and he scanned it and it's the secondary air pump, but I decided to not fix it because it was running fine.
A week ago the engine started shutting off when braking or even backing up really slowly. I took it to the mechanic and he suspected the fuel I was using and yes I was using regular gas (I know, stupid me listening to the advice of two friends who said using regular gas on a BMW is fine). So the mechanic recommended I start using Octane 91 from Shell and an Octane booster on my current regular gas tank. The car started acting a bit better but it's still far from perfect. So I took it back to the mechanic. When scanning it the secondary air pump fault did not show up but the crank shaft sensor fault showed up, and something about the air control valve or something. The mechanic could not understand how the faults changed from one thing to another. And of course I don't want to replace everything to find the problem!
Here are some of the symptoms:
1) The engine would shake and run irregularly when I started it up. Especially after a long period of it not working.
2) The engine would sometimes shuts down when I brake hard. The RPM would go down and the engine stalls.
3) If I take my foot of the brake while the engine is stalling then it would save itself from shutting down and it would keep running.
4) This happened a couple of times: power loss. It was so scary one time when I was trying to make a left turn and the car would just not go!
5) The RPM would go up then down, then up again! This happened a couple of times: the RPM would reach 2,000 RPM and while I was still pressing on the gas the RPM would drop to say 1,500 RPM then go up again.
Today the mechanic found a loose hose so he suspected a vacuum leak and so he fixed it. Afterwards at a test drive the car still shut down.
There is less power loss now; the car is more responsive now. But the engine still shuts down on a hard brake.
I googled the problem and it seems that there could be a tone of things of which my mechanic ruled out most of them. Here is the list:
-battery and alternator not holding charge
-torn brake booster
-oil separator valve has a crack
-idle control valve
-CPS (I don't even know what this is!)
-MAF (I don't even know what this is!)
Anyway, I am taking the car to RMP Motors this evening for a second opinion. (My mechanic recommended I seek a second opinion to be sure what is causing this problem, and the shake problem discussed in another thread.)
I don't mind spending money to fix the problem, but first I need to know what the problem is! Has anyone experienced exact symptoms with his E39, who can help? Please!