I bought this car in in mint condition, with 75k miles on it. Thorough records left in the glove box show Inspection 2 was done at 66k miles.

Almost from the time I got it, the car has been sluggish. It accelerates through all gears, it just feels uninspired. Very rarely, the car has whole days, or just moments, of brilliance - where it drives like a BMW.

This was why had Inspection 2 done AGAIN at 80k miles**.

There is no change. However, from 83k miles I have learnt to bring out the performance with Lucas Fuel Injector Cleaner. At best, performance bursts last a few days after an application. At worst, these last a couple of drives in a day.

I'm wondering if I'm on the right track, and if continued dosages of Lucas will clean out whatever.

Couple of things to note:-
- In very cold weather, RPMs fluctuate with a certain regularity.
- The Vanos seals have been checked to be intact.
- **between 79k and 81k miles , there was an intermittent sound that would come up if the car was running, but stationery. E.g. Driving off after a stop at a traffic light. The sound was a rough sound that matched the engine's loudness and softness.
- Hot or cold weather has nothing to do with it.
- I've been in 2 other E39s that are in a much worse condition, but at least drive peppier.

What gives?

check your fuel filter. my buddies m3 did the same stuff. just an idea

i would recommend you replace the MAF, and the O2 sensors if they haven't already been changed. Those two things can be responsible for a lot of things, rough idle, power loss, etc... If the fuel enhancement worked, what type of fuel are you putting in? In all the Bimmers I've owned, I always put the 93 octane in, and I've never had any problems with it. My cousin on the other hand would use the cheapest crap (87), and he ran into a lot of problems with knocking.