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Discussion Starter #1
Hi guys. New here. I read on here for hours but couldn't find a post matching my symptoms.

2005 330xi. 160,000 mi. Hoping to get a little expert advice trying to pinpoint this misfire problem I'm having.

2 weeks ago I started having these rough idle/random misfires right after i got gas somewhere. Maybe coincidence, maybe not. And then symptoms would persist only after its been driven a while and plenty warm. And only starts at low rpms when idling somewhere. In the beginning if it happened, i would just shut the car off and restart it and the symptoms would go away for the time being. Now it's becoming worse and more often, almost anytime i come to a stop. The idle will suddenly dip real low, run really rough and start misfiring.

The first time it happened i took it to the mechanic and he said he pulled SAP codes. Lean codes. And o2 sensor codes. He did not get any misfire codes. I apologize for the lack of specific codes and my lack of education on the matter. I had him replace the o2 sensors. Didn't replace the SAP as he suggested that most likely wouldn't cause symptoms i described.

The o2 made a huge difference with rpm and mpg but was still having random misfires. When I took it back he ran diagnostics on it again and had several misfire codes. 1, 4, and 5. He said those cylinder misfires are usually correlated with a failing head gasket. He did a compression test on cylinders and said misfiring cylinders were low. I forget the exact numbers. He said there is no way to know for sure until do a smoke test. But can still be driven.

Following this, I drove for 3 days without an issue. was getting excited maybe the problem worked itself out. Bad gas or something or other. I drove fairly long distance, stopped to refuel, and then it started misfiring/trying to stall.

I understand the next step is to do a smoke test and leak down test on cylinders. (Is this different than a compression test?) I'm hoping it's not the HG obviously.

I'm wondering if anyone else has had similar symptoms and what the issue was. I'm wondering what the process entails that'll determine if it is the HG or not. I'm wondering if anyone could suggest another possibility to have my mechanic check/replace. I'm wondering if the SAP (secondary air pump) could cause any such symptoms I've described.

I'm wondering if this car is worth saving. I've already put about $4000 of work into it.

Thank you for reading. And thank you if you could help in any way or suggest anything
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