Welcome to the forum.

Let’s get you set up
Have a read through the IMPORTANT LINKS page. There you will find threads about how to ask for help as well as fixes and advice on many of the common E46 problems.

A couple of helpful web pages:

• Part numbers and exploded diagrams: www.RealOEM.com. Enter the last 7 digits of you VIN into the search tool. Bookmark the results, you’ll be back many times. Then browse for part numbers specific to your car.
• Build spec. You’ll need a build spec as some parts have different versions for different spec vehicles. This link may or may not work, but it will give you a lead on getting a VIN decode: Free BMW VIN Decoder : ///M Decoder
• E46 wiring diagrams: BMW WDS Online

Now let’s get back to your car problem.

We are going to need some more information to be able to help you:

1. What warning lights come up on the dash?
2. Car there any trouble codes stored in the DME?
3. Have you smoke tested the engine to see if it is being caused by a vacuum leak? See more on lean codes, vacuum leaks and smoke testing on the Important Links page.

 

Check engine light on? Scan for the trouble codes? I would suspect some misfire based on your description.

 

Hello. I had a similar problem recently on my e46 m52b20tu. Idles could drop to 500 or lower even when driving, for example, smooth acceleration, jerks occurred ... thrust either disappeared abruptly or reappeared ... there were no codes at all ... conducted a smoke test with a homemade smoke generator and found a vacuum leak ... was the pipe that is put on the throttle valve is cracked. After the replacement, the problem is gone. This does not mean that you have the same problem, but it may be one of the options for poor engine performance.

 

Do the usual by checking for engine codes and doing a smoke test to find any vacuum leaks, maybe take the idle valve off to clean it out too. If they come back all good then time to dig a little deeper but no point worrying you about other things until the basics are looked at.

 

I had a similair problem, had a rough idle and some loss of power at mid RPM. I replaced the sparkplugs, checked the injectors and the ignition coils. Even checked my fuelfilter and pump but I couldn't find the problem. My knowledge only goes to a certain extend so after much troubleshooting I brought it to the garage and they found the problem after a whole day of searching. Evidently it was the DISA valve, this valve basically controls the airflow to the engine and it changes it depending on if it is idling or not. if your engine randomly rattles when idling and idles rough this is probably the problem, it may be not but it is worth reading about to see if the problems relate to your engine.