Engine misfire story and question

Ok, so I have a 2000 323i w/about 120K on it. I have owned it since 89k. Engine is all stock as far as I know. So once in a while while idling when the engine is hot, the engine light will come on and the car will idle really rough. I can shut it off and restart immediately and it goes away although the engine light stays on for a few drive cycles. I did nothing about this because it was pretty intermittent and seemed to go away. I did have it scanned at Advanced Auto and all I got was a p0306 code and a p1250. I wasnt sure what to make of it so I just ignored it for the time being. This took place some time last year. Then about 2-3 months ago the engine started making a really annoying squeak at idle. It would disappear immediately above idle, but it was driving me nuts. Also, I have noticed a degradation in power over the last 6 months or so. So, I start by replacing the idler pulley. It was bad and the new one seemed to quiet the engine a little, but the squeak was still there. Well, after replacing the tensioner pulley on the alternator belt, it was still there. I finally figured that out and the tensioner itself was moving back and forth just a little and causing the squeak (mechanical tensioner). So i replaced the tensioner and i realized the water pump bearing was bad. I replaced the water pump then also and a new belt and the squeak is gone. So onto my next problem. I did a little digging and found a tear in the lower intake boot on the elbow that goes to the idle control valve. Now here is my hypothesis, and please dont laugh because I am really not that intelligent on the matter. When you start the engine and it is cold, the MAF measures the air coming into the engine. When the air exits the engine, the o2 sensors measure the burnt fuel/air mixture and adjust accordingly. Now, I think I read somewhere that some of the o2 sensors dont actually read until the engine is warm. Could this extra air entering the system cause the mixture to adjust beyond what is normal and cause the misfire? Does it make sense that it only happens at idle and if you idle for an extended period of time? Also, the idle has become increasingly rough, and I think that all the dirty air that has been getting into the ICV has gummed it up a bit. I have ordered a new boot, but wont see it for a few days, and in the mean time I have duct taped the tear the best I could to try to seal it up. I also did the plastic bag suction test on the oil cap and it seemed normal. I recently put Bosch platinum +4 plugs in, but am planning on taking them back and getting some ngk iridium plugs. WHat do you guys think? Am I on the right path?

Also, I took the DISA apart and it seemed to function normally. You can close it with some resistance and then it spring back.

Also, I want to throw out a thanks to all the contributors to this site. It has been invaluable as far as information goes. I now know more about these cars than I ever thought I could.

I also plan on doing the vanos upgrade soon. I will explain why. When the engine is running, I can give it gas and run the engine up to 1500 rpm's and hold the pedal steady, and almost immediately, the revs drop 2-3 hundred while the gas pedal is stationary. Not sure what this is, but I figured it was related to a failing vanos. Thanks

Update-
Replaced the plugs today with NGKBKR6EQUP and almost got into a fight with the girl at the auto parts store. She did not want to take back the Bosch plugs that I bought last week because she said they were designed for my car. She also told me that the internet is not a reliable source.

well SHE IS not a reliable source.
Usually bad MAF could cause misfire, camshaft position sensor causes it as well....
If you never had replaced MAF sensor, get a new one. Or, you could get a MAF sensor for hyundai sonata, it's exactly same as BMW..
follow this link for more info
http://forum.e46fanatics.com/showthr...=713155&page=3

jkline805 - Did you ever solve the rough idle after warm up? I am having the exact same issue on a '99 328i.

Hey,
I just replaced the my plugs with Bosch platinum +4, replaced my fuel filter, the upstream 02 sensors (Bosch direct-fit), and some other 100k miles stuff... I was having a rough idle on cold start, plus some fuel trim malfunction, evap emissions leak, and upstream o2 sensor codes. I found a tear in the intake boot closest to the engine, it was on the smaller branch off part, and I have also rigged it up with duct tape and a zip-tie for now. Part is on order.

After the plugs, but before discovering the tear, I got some misfire codes on 3 cylinders and I am still getting the 02 codes P1188 and P1189.

Is there a problem with using the Bosch plugs? I did see that it had the NGK/BMW plugs in it. Should I replace the Bosch plugs with NGK? Too bad I threw the boxes away.. $5.99/each...

Covering the tear in the intake boot has definitely helped the idle, but I haven't reset the codes to see if it is still misfiring..

Any advice would be appreciated.

Thanks,
Ben

Most def. could be the MAF. Sounds similar to what I was dealing with. I replaced the boots and MAF.