Need help diagnosing rough idle

TWO STEP TEX · 07-27-2022, 02:50 PM

Hi there. Backstory: car was running great with MHD OTS tune. One weekend in April decided to put in a catless downpipe. Managed to get it in, but couldn't deal with the fumes (car is mostly driven in NYC with lots of stop and go traffic). Decided to go back to OEM cat but one of the studs broke during removal so I took it to a shop to press out the stud and reinstall (I didn't have the patience to deal with the v band again, nor a place to do it). The mechanic stated I had some vacuum leaks and they fixed them (news to me) and all was.good. I noticed a strong smell of exhaust fumes and I suspect the gasket from cat to turbo is bad and needs to be replaced. Car has been running fine, besides a sometimes unsteady idle. I was making some changes to the XP trans flash the other day and the car started running incredibly rough. Stuttering and struggling to idle. I figured the MAF might be bad so I unplugged it. Car runs fine when unplugged so ordered new MAF. Put new MAF in and it still runs like garbage when plugged in. I'm looking for suggestions from you experienced N55 folks. Much appreciated.

wheela · 07-27-2022, 08:39 PM

If it idles fine with the maf unplugged, and a new maf made no difference, i'm guessing you have an air leak. Here's a thread with almost identical issue from over on e90 post:
https://www.e90post.com/forums/showthread.php?t=1939856

wheela · 07-27-2022, 08:44 PM

Can you post a log of idling with the maf plugged in? It would be good to see what ltft and stft are looking like.

TWO STEP TEX · 07-28-2022, 05:10 PM

Thanks for the link. I plan on getting under the car this weekend to troubleshoot possible air leaks. On my way out to NJ it started throwing valvetronic codes so now I'm trying to figure that out as well. Initially it was 2E0F, after the calibrating it using the Protocol app I'm getting 2D45.

Is love to post a log, however I'm not terribly tech savvy. Can you please clarify "ltft" and"stft"? Is that short term and long term fuel trim?

TWO STEP TEX · 08-30-2022, 09:22 AM

Update: Took the car to a reputable shop and I'm told the valve cover is cracked (breather). I replaced it last year but decided to try and save money by using the generic part. I saved like 250.00 to be in the same place a year later. I don't have anywhere to do it myself this time so it's going to cost 1400.00 to get it done. Kill me. Hopefully my extended warranty covers it but I'm not holding my breath. Oh also, I replaced the turbo inlet with an aluminum unit because the plastic bracket was broken. When screwing it in the bolt snapped off into the block lol. If it's not plastic breaking, it's these damn aluminum bolts.

Side note:
I was having issues with valvetronic not resetting. I tried manually resetting it through MHD and Pro Tool with no luck. I tried the gas pedal method and that didn't work either. Although I could hear it reset, I was still getting codes. Only until I flashed the ECU back to stock did it reset the valvetronic motor. It took me forever to find this solution so I wanted to document it here.

07-27-2022, 02:50 PM	#1
TWO STEP TEX Enlisted Member 15 Rep 47 Posts Drives: BMW 135i Join Date: Oct 2021 Location: New York City iTrader: (0)	Need help diagnosing rough idle Hi there. Backstory: car was running great with MHD OTS tune. One weekend in April decided to put in a catless downpipe. Managed to get it in, but couldn't deal with the fumes (car is mostly driven in NYC with lots of stop and go traffic). Decided to go back to OEM cat but one of the studs broke during removal so I took it to a shop to press out the stud and reinstall (I didn't have the patience to deal with the v band again, nor a place to do it). The mechanic stated I had some vacuum leaks and they fixed them (news to me) and all was.good. I noticed a strong smell of exhaust fumes and I suspect the gasket from cat to turbo is bad and needs to be replaced. Car has been running fine, besides a sometimes unsteady idle. I was making some changes to the XP trans flash the other day and the car started running incredibly rough. Stuttering and struggling to idle. I figured the MAF might be bad so I unplugged it. Car runs fine when unplugged so ordered new MAF. Put new MAF in and it still runs like garbage when plugged in. I'm looking for suggestions from you experienced N55 folks. Much appreciated.
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07-27-2022, 08:39 PM	#2
wheela Captain 279 Rep 696 Posts Drives: 2015 BMW X1 35i M-sport Join Date: Mar 2021 Location: Twin Cities MN iTrader: (0)	If it idles fine with the maf unplugged, and a new maf made no difference, i'm guessing you have an air leak. Here's a thread with almost identical issue from over on e90 post: https://www.e90post.com/forums/showthread.php?t=1939856
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07-27-2022, 08:44 PM	#3
wheela Captain 279 Rep 696 Posts Drives: 2015 BMW X1 35i M-sport Join Date: Mar 2021 Location: Twin Cities MN iTrader: (0)	Can you post a log of idling with the maf plugged in? It would be good to see what ltft and stft are looking like.
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07-28-2022, 05:10 PM	#4
TWO STEP TEX Enlisted Member 15 Rep 47 Posts Drives: BMW 135i Join Date: Oct 2021 Location: New York City iTrader: (0)	Thanks for the link. I plan on getting under the car this weekend to troubleshoot possible air leaks. On my way out to NJ it started throwing valvetronic codes so now I'm trying to figure that out as well. Initially it was 2E0F, after the calibrating it using the Protocol app I'm getting 2D45. Is love to post a log, however I'm not terribly tech savvy. Can you please clarify "ltft" and"stft"? Is that short term and long term fuel trim?
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08-30-2022, 09:22 AM	#5
TWO STEP TEX Enlisted Member 15 Rep 47 Posts Drives: BMW 135i Join Date: Oct 2021 Location: New York City iTrader: (0)	Update: Took the car to a reputable shop and I'm told the valve cover is cracked (breather). I replaced it last year but decided to try and save money by using the generic part. I saved like 250.00 to be in the same place a year later. I don't have anywhere to do it myself this time so it's going to cost 1400.00 to get it done. Kill me. Hopefully my extended warranty covers it but I'm not holding my breath. Oh also, I replaced the turbo inlet with an aluminum unit because the plastic bracket was broken. When screwing it in the bolt snapped off into the block lol. If it's not plastic breaking, it's these damn aluminum bolts. Side note: I was having issues with valvetronic not resetting. I tried manually resetting it through MHD and Pro Tool with no luck. I tried the gas pedal method and that didn't work either. Although I could hear it reset, I was still getting codes. Only until I flashed the ECU back to stock did it reset the valvetronic motor. It took me forever to find this solution so I wanted to document it here.
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