engine performance 325

[Belal Salem]

When I accelerate the car, it goes very well and quickly until it reaches about 2.25rpm then it doesn't accept any acceleration but it starts to accelerate slowley until it passes 3rpm it continue accelerating normaly in good performance,
What do you think that make the engine stop responding in this range of the rpm ( from 2.25-3rpm)?

Also, when I fix my speed to about 120 km/h (about 2.5rpm), the engine works randomly accelerate and deaccelerate when the same amount of the pedal is pushed, I feel a drag as if a cylinder doesn't recieve ignition then it recieves then not ... and so on, or as if the engine tends to stop then start and so on... but this is not what happens as I guess. and in that time I have black smoke off the exhaust.

Note: the engine is 325 single vanous (M50), automatic Japan transmision.

[3050rpm]

I sometimes have a similar problem, only in the 1800-2000 rpm range, where there seems to be a flat spot in the engine response, almost as it the car is fighting me to get beyond that point. Beyond that it's fine. I'm not sure what the problem might be, I heard somewhere that the solenoid to the VANOS (if there is such a thing) could be at fault, but I haven't bothered to check things out to that extent. On a more mundane level, have all the usual tune-up things been taken care of (plugs, filters, etc.) and have you tried running some injection cleaner through?

[mullethunter3]

The VANOS solenoid does exist. I'm not sure that the symptoms you are describing are due to a bad solenoid, but then again, my car doesn't have VANOS. As for the cost of one? For a 1995 M3 --> $500.

[B_w.]

are you throwing any codes?

[jromanc78]

I had the Vanos Adjusting Unit and the Vanos Solenoid replaced and that didn't fix the problem.

[EuroStyle]

when my car did that it turned out to be a faulty o2 sensor. 150.00 to replace it, and the car ran fine.