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Discussion Starter · #1 ·
Hello E46 Fanatics,

My 2002 E46 is having an issue that I can't seem fix. After my car is warmed up after about 15 minutes or so, it starts to run rough with some minor shaking. My service engine light switches on also.

At first, I figured that my spark plugs needed replaced. Maybe one was fouled and misfiring. I ended up replacing all with NGK Platinums. Awesome.

About 15 minutes later, same problem. I thought it could be one of my ignition coils. So, I did the "ol' pull the plugs on each coil and see which one DOESN'T degrade the engine" trick.

Found one that had no reaction, and replaced it with a brand new Bosch ignition coil. Awesome.

Now the same problem AGAIN...Unplugged the new ignition coil and had no response or downgrade again!!! So I figured I'd use process of elimination and swap places with one that was degrading when I unplugged it.

Any coil that plugs into the second "hole" closest to the window never degrades.

What the hell do I do now? Is it the plug? Flapper?

Please help, obviously I know jack crap about car terminology. :cry:

Premium Member
28,872 Posts
So what you really need is an OBDII tool that can read codes and Live/Realtime data so you can get a better idea as to what is going on.

Most idle misfires are NOT coil or plug related. They are most often due to Lean fuel mixture problems or engine mechanical problems.

For the first round, we will assume there is not an engine mechanical problem, but it may need to be ruled out later on. There is no history as to how and when this misfire started and what happened to the engine just before the misfire occurred.

For $30 or less you can purchase your own OBDII smart phone App and interface or for around $50 you can purchase a decent stand alone scan tool. DO NOT purchase a stand along scan tool from your local auto parts store, you WILL regret it. FYI, I really DESPISE the "orange" tools you will most likely have available locally.

You could possibly get codes read for free at your local auto parts store. This will likely give you some idea where to start.

Here is some more info to read:

You need to read the first 2 links below in my signature.

Need to see Freeze Frame info if the SES/CEL/MIL is on and Fuel Trim values at both warm idle and a steady highway cruise between 45-60 MPH.

Read this thread - http://forum.e46fanatics.com/showthread.php?t=1057387

Read my "BMW 20 Questions" comments in this thread - http://forum.e46fanatics.com/showthread.php?t=1059972

Search YouTube for Scotty Smoke Test. Do what Scotty does or build a tester from related video. Remove the oil fill cap and make sure the crankcase fills up with smoke, put the oil fill cap back on and check for leaks around the valve cover, oil fill cap, dipstick tube and CCV hoses. Cracked valve covers are pretty common on the E46 as it ages.

Good luck.
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