Re: Intermitent poor performance--any ideas? (archive)

I have a 93 750. On three different occassions, the engine has exhibited the following symptoms:
1. vibration, though not extreme
2. low power, can barely move the car
3. (a) idle won't hold and the engine stalls OR (b) the idle holds at about 4 hundred rpm and the engine clearly struggles to keep running
4. if I turn off the ignition and restart the car, it fires up just like nothing ever happened and it runs fine.
The most perplexing thing is that despite the dual DME and other dual systems it DOESN'T seem like the problem is confined to one side of the motor. If one side was cutting out, that would explain the slight vibration and low power, but not the inability to hold idle or the stalling of the entire engine, right?
The fuel lines have been cleaned with compressed air, so nothing is plugged. Also, I recently replaced both fuel pressure regulators to solve a different problem. The current problem existed before and after the replacement.
The car passed an emissions test just a couple days ago, with flying colors.
The ECU does not show any fault codes.
I'm stumped, anyone out there know what the problem is?

I had almost exactly the same symptoms very seldom over a period of 3 years, especially the struggle to idle action (about 3 times in total). Amazingly enough replacing BOTH relays that supply power to each injector bank stopped the problem completely.
Maybe yours is the same?!
Brian P.

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