E30 was totaled in 2020, bashed quarter panel. I gutted a shell to start fresh and transferred all components to this shell, wiring harness, and now the original engine which ran great has an idle misfire. The car drives great and never stumbles on acceleration or cruising. On cold starts the idle is at its most calm state but I’ve noticed the exhaust smoke comes out in short small puffs even during cold start. As the car gets warmer the misfire gets worse, once driven for 15-20 minuets, the idle will be more erratic but not as erratic at all like a whole cylinder misfire. Ive done a smoke test and found leaks on the rocker plugs, replaced that, no change at all, I had some exhaust leaks going on from old headers, since then i have installed my super sprint headers back on and also fixed another leak near the header coupling to the cat but issue still persists but may have improved a bit. Ive put at least 3-4k miles on the car and the situation has only slightly improved but has not gotten worse, plugs look in great condition after these miles, cylinder inspection with camera, cylinders look good, valves dont appear to have taken a hit but i Plan to do cylinder tests soon. One thing that is puzzling is, the misfire is very consistent, it does not come and go at an irregular pattern, its the same exact pattern, its very rotation based consistent if that makes sense which makes me think its not a vacuum leak but its still on my radar. I’ve changed cap/rotor, spark plugs, TPS, both head mounted coolant sensors, fuel pumps/filter, tested new plug wires (these are only 3-4 years old) CPS is 2017, 02 sensor 2017. Im kind of running out of ideas, one thing I’ve notice is it’s much better with the 02 sensor disconnected. IM very close to buying another one but just wanted to check with y’all as i have a feeling its not the 02,
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Could be the O2 relay and not the sensor. Did you buy a bosch sensor? -
Yes Bosch sensor, and actual that’s 8 years old so it could be time. After driving today it reminded me. Sometimes my idle will be around 1k which is leading me in the direction of vacuum or an air flow sensor. I never thought about the 02 relay. I believe I may have an old 02 that I replaced diagnosing an issue once before that turned out not to be the problem so if I can find I’ll give it a try and the relay. Also forgot to mention check engine is on at idle goes away under load.Comment
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My M20 idles better than any BMW I have ever owned with: Ford 4 pintle injectors 19lb, SSSQUID chip 93, DENSO Iridium plugs and a DENSO oxygen sensor. Low end driving was dramatically better after I changed all of these parts together. MPG is improved as well.Comment
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Thanks for your comment. I had a rough period where the block needed to be rebuilt, after swapping blocks with one with 90k miles I had a really good running m20, the head also had some refresh done almost 15 years ago after snapping a timing belt. I forgot to mention’s above that I’ve replace injectors with stock Bosch, no change in the drive at all, 35 year old injectors we’re fine. (I want to sssquid tune as well!) I have denso plugs also but did not know they offered 02 sensors.Originally posted by packratbimmer View PostComment
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