Rough idle all of a sudden....I'm stumped.

iqraceworks · 06-03-2023, 10:29 AM

For some reason, out of the blue, one day last week I noticed that my car developed a slightly rough idle. I was at a stop light and noticed I could feel it through the seat. As soon as I get the motor off idle, it smooths out and feels like normal. Car still runs like a top....just that rough idle. It's bad enough where I can see the tach jump at all, but I can feel it through the seat and when I put my hand on the motor.

I started with the basics....pulled all the plugs and found a wet one. Great, leaky injector...that must be it. Replaced the injector, no change in the idle.

I then reset all the motor adaptations.....no change in the idle.

Scanned for codes just for the heck of it...nothing.

I ran a log trying to see if I could see anything...nothing. ARF's, STFTs, LPFP,HPFP, everything looks fine....so signs of anything odd.

I went ahead and put in all new plugs and coils (thanks FCP!).....still no change in the rough idle.

Checked for any leaking vacuum lines, or anything else odd under the hood. nothing. Valve cover is a new OEM one with only around 6K miles on it. Valve were cleaned about 15K miles ago.

What's some other things that could cause a slightly rough idle? I'm out of ideas.

Bimmer_Bro · 06-03-2023, 09:24 PM

Quote:

Originally Posted by iqraceworks

For some reason, out of the blue, one day last week I noticed that my car developed a slightly rough idle. I was at a stop light and noticed I could feel it through the seat. As soon as I get the motor off idle, it smooths out and feels like normal. Car still runs like a top....just that rough idle. It's bad enough where I can see the tach jump at all, but I can feel it through the seat and when I put my hand on the motor.

I started with the basics....pulled all the plugs and found a wet one. Great, leaky injector...that must be it. Replaced the injector, no change in the idle.

I then reset all the motor adaptations.....no change in the idle.

Scanned for codes just for the heck of it...nothing.

I ran a log trying to see if I could see anything...nothing. ARF's, STFTs, LPFP,HPFP, everything looks fine....so signs of anything odd.

I went ahead and put in all new plugs and coils (thanks FCP!).....still no change in the rough idle.

Checked for any leaking vacuum lines, or anything else odd under the hood. nothing. Valve cover is a new OEM one with only around 6K miles on it. Valve were cleaned about 15K miles ago.

What's some other things that could cause a slightly rough idle? I'm out of ideas.

How are your Vanos Solenoids ? Tried cleaning them ?

iqraceworks · 06-03-2023, 09:53 PM

Quote:

Originally Posted by Bimmer_Bro

How are your Vanos Solenoids ? Tried cleaning them ?

I've never messed with them...ever. if they are dirty can they cause a rough idle issue? Wouldn't it throw a code if something was wrong with them?

Bimmer_Bro · 06-03-2023, 09:57 PM

Quote:

Originally Posted by iqraceworks

I've never messed with them...ever. if they are dirty can they cause a rough idle issue? Wouldn't it throw a code if something was wrong with them?

Usually code or missfire but they are on the list of items for rough idle. Seems like you have done mostly everything else

AWD Addict · 06-05-2023, 09:31 AM

Mines had this off and on for 15 years. I've tried everything.

I recently just ripped out perfectly good index 11 injectors to plug in some 12s. No dice. Brand new coilpacks, plugs, fuel pumps etc.

Baffling.

I think this car is just hyper bitchy about fuels, even name brand fuels.

Yotaismygame · 06-05-2023, 01:05 PM

Quote:

Originally Posted by iqraceworks

I've never messed with them...ever. if they are dirty can they cause a rough idle issue? Wouldn't it throw a code if something was wrong with them?

Pending mileage of the car if you haven't replaced them yet I would if you plan to inspect them. Not all that much for new oem ones.

Yes they can cause a rough idle.

https://bmwtuning.co/vanos-solenoid-replacement/

iqraceworks · 06-05-2023, 06:05 PM

I had a little more time today to do some more troubleshooting. Looked at LTFT's (they were both equal for the most part), looked at vanos require and vanos actual for intake and exhaust (they were both meeting required numbers). I think at this point I need to start pulling injectors and replacing each one with a different one, and see if there is an injector with a funky spray pattern or something.......all the log data looks fine, so maybe that's it? If that doesn't cure the issue....I'll go through all the vacuum lines again and recheck everything for a vacuum leak...but it sure doesn't feel like a vacuum leak.

I have a new turbo and injectors that I need to put in my diesel truck this week....so I'm going to take care of that first, and then get back to the 335i.

Thanks for all the ideas guys...I hope I figure this out. Even though the car runs great....this bumpy idle thing is driving me nuts.

06-03-2023, 10:29 AM	#1
iqraceworks Brigadier General 2114 Rep 3,811 Posts Drives: 2007 335i Join Date: Aug 2019 Location: Missouri iTrader: (0)	Rough idle all of a sudden....I'm stumped. For some reason, out of the blue, one day last week I noticed that my car developed a slightly rough idle. I was at a stop light and noticed I could feel it through the seat. As soon as I get the motor off idle, it smooths out and feels like normal. Car still runs like a top....just that rough idle. It's bad enough where I can see the tach jump at all, but I can feel it through the seat and when I put my hand on the motor. I started with the basics....pulled all the plugs and found a wet one. Great, leaky injector...that must be it. Replaced the injector, no change in the idle. I then reset all the motor adaptations.....no change in the idle. Scanned for codes just for the heck of it...nothing. I ran a log trying to see if I could see anything...nothing. ARF's, STFTs, LPFP,HPFP, everything looks fine....so signs of anything odd. I went ahead and put in all new plugs and coils (thanks FCP!).....still no change in the rough idle. Checked for any leaking vacuum lines, or anything else odd under the hood. nothing. Valve cover is a new OEM one with only around 6K miles on it. Valve were cleaned about 15K miles ago. What's some other things that could cause a slightly rough idle? I'm out of ideas. __________________ 2007 335i, BMS DCI, BMS Chargepipe w/Tial BOV, ARM Catless Downpipes, silicone inlets, Bilstein B12 Prokit Suspension, Whiteline subframe bushings, Front/Rear M3 control arms, G-Plus FMIC, Stage 2 LPFP, Custom E40 tune by Justin (V8Bait), xHP stage 3 transmission flash, RB Two Turbos....10.90 @ 128mph Last edited by iqraceworks; 06-03-2023 at 10:39 AM..
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06-05-2023, 09:31 AM	#5
AWD Addict Chief Executive 407 Rep 2,930 Posts Drives: 2008 335xi 6spd Coupe Join Date: Dec 2007 Location: Boston iTrader: (1) Garage List 2008 335xi [0.00]	Mines had this off and on for 15 years. I've tried everything. I recently just ripped out perfectly good index 11 injectors to plug in some 12s. No dice. Brand new coilpacks, plugs, fuel pumps etc. Baffling. I think this car is just hyper bitchy about fuels, even name brand fuels.
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06-05-2023, 06:05 PM	#7
iqraceworks Brigadier General 2114 Rep 3,811 Posts Drives: 2007 335i Join Date: Aug 2019 Location: Missouri iTrader: (0)	I had a little more time today to do some more troubleshooting. Looked at LTFT's (they were both equal for the most part), looked at vanos require and vanos actual for intake and exhaust (they were both meeting required numbers). I think at this point I need to start pulling injectors and replacing each one with a different one, and see if there is an injector with a funky spray pattern or something.......all the log data looks fine, so maybe that's it? If that doesn't cure the issue....I'll go through all the vacuum lines again and recheck everything for a vacuum leak...but it sure doesn't feel like a vacuum leak. I have a new turbo and injectors that I need to put in my diesel truck this week....so I'm going to take care of that first, and then get back to the 335i. Thanks for all the ideas guys...I hope I figure this out. Even though the car runs great....this bumpy idle thing is driving me nuts.
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