Engine feels Rough and Power lost [Archive] - Bimmerfest - BMW Forums

: Engine feels Rough and Power lost

02-12-2006, 01:15 PM
I have a manual 99 323i with 128k.

I loved the feel of the smoothness of the engine and how torquy it feels. The harder you step on the pedal the more power and smoothness you get. Passing someone at 60MPH was great. Now, I canít even do that.

I started loosing power and the engine started sounding rough when accelerating. So I decided to change the spark plugs. The car drove great for a week then the engine started feeling rough and the power disappeared. Passing someone at 60 MPH isnít easy anymore. It feels like the engine has to work hard just to pass someone.

I decided to change the spark plug boots, then power comes back for a week, Then gone with the wind again.

Change the intake cam sensor power comes back for one week then disappears again.

Changed 1 precat o2 sensor and power comes back for 3 weeks and then it disappears again.

Changed the second Precat sensor and the power comes back and engine feels smooth. 2 days later, power disappears.

I take the car to 2 different shops to perform a diagnostic. The test said that the Fuel cap had an error; the thermostat was stuck open and security issue with key 2.

Car drives fine. No check engine light and everything is fine says the Mechanic.

I tell him, I drive this car all the time I know my car. I just want it fixed.

Why is it that when I change a part, power and smoothness comes back and after a week or so itís gone?

Is the ECU adjusting the timing? What is happening? Any ideas or suggestions would be great.

02-12-2006, 02:14 PM
SOunds like it could be a clogged cat.

02-12-2006, 03:21 PM
If this is so, then why everytime I change a part the smoothness and power comes back and last about a week or so?

Are there any tricks I can use to see if this could be the problem?

02-12-2006, 04:08 PM
how about a plugged fuel filter? I have had that happen on other cars. It can drive you nuts. cheap to change tho...

02-12-2006, 04:41 PM
That was the only part I changed that didn't make a difference. I don't think it's the fuel filter. How can I see if the cat is the problem?

02-13-2006, 06:18 PM
I would change the Fuel Filter, Plugs, Plug wires and the Catalytic converter. Your car should feel good after:)

Fast Bob
02-13-2006, 07:27 PM
I`ve never seen one for a BMW, but there are so-called "test pipes" available for Detroit iron that are nothing more than a spacer to replace the cat. If not available from an auto parts store, any good muffler shop can fab one up for not much money.
Have you checked your ignition`s coil?


02-13-2006, 07:29 PM
It is a federal offense to run without a cat on a car so equipped from the factory.

Fast Bob
02-13-2006, 07:31 PM
For testing purposes only, of course....


02-14-2006, 06:35 PM

02-14-2006, 08:28 PM
That's what I was thinking. Maybe coils going bad or a bad ground in the ignition system. Any work on the car may move or bump them so they work for a while.

02-15-2006, 05:38 AM
1. I agree coils.


2. Clogged and or bad fuel injector.

02-15-2006, 07:28 AM
I took a chance and installed an old o2 sensor from a old 94 Honda accord I use to have. It worked. The power and torque is back I've been driving it for 2 days now. No check engine light on and great fuel mileage.

I changed the first pre-cat o2 sensor, but never changed the second one. It seems as if a bad or lazy o2 sensor will cause the engine to run lean. I wonder why the check engine light didn't come on to tell me this.

I appreciate everyoneís help on this.