Intermittent/tricky rough idle and run - Ideas?

[Eidolon]

So this is apparently my first post here. Hello all! But I call upon the expertise of the owners here at Bimmerforums to help me out. My 1996 E36 M3 coupé has a rather tricky malady.

Here are the symptoms.

• Intermittently, when cold, significantly rough idle or run through the revs, as though the engine is firing on five out of six cylinders. Sometimes continues on a warm start unchanged from previous behavior, but never occurs freshly on a warm start.
• Cylinder 1 Misfire code P0301. ONLY ever this code. No others, such as lean (P017x) or otherwise.
• Once the engine is warm, it seems to run much smoother, though still not quite like a sewing machine, as one would expect of a BMW inline-6.
• Just this morning, on the way to work, it was running horribly. After ten minutes on the road, at a stop sign, I turned the engine on and off. It went from running as though it was missing a cylinder to buttery smooth. The only thing I changed was an engine kill and restart.

This is the beast in question:


When it first occurred, I pulled the spark plug on cylinder 1 and it looked fine. No severe fouling or gap between electrodes. I swapped the coil packs on cylinders 1 and 2, but it had no effect.

Details on the car and work done on it:

• 1996 M3 coupe in Boston Green Metallic with Modena interior with manual Vader seats
• Purchased from Beaufort, SC, it was the previous owner's track car. Now it's mine. That's its intended destiny: track visits to VIR with the Tarheel BMW CCA.
• Already many track mods: electric radiator fan, Racing Dynamics sway bars, H&R Race springs with Bilstein shocks, solid rear subframe mounts, poly diff mounts, TMS rear lower control arms, poly RTAB bushings, Z3 steering rack, poly front LCA bushings, Ground Control front camber plates, ASC delete, TMS Shark stage 1 tune.
• Many of the intake hoses, suspension components, etc., were unfortunately worn out when I got the car, so I've been working to replace them.

I've been chasing this particular issue for a while. At first, after finding some worn out intake components, I thought it was just an intake leak. I found a torn ICV hose and intake boot (ASC has been removed/deleted).

Torn ICV hose, patched with electrical tape. Seriously.


Torn Bimmerworld silicone intake boot, also patched with electrical tape:


I cut out the bad portions of these hoses and connected them, but the car still ran rough. So I completely removed the intake side of the engine...


I replaced the following:

• Intake-manifold-to-head gaskets
• Throttle-body-to-manifold gasket
• ICV hose (and cleaned the ICV itself using MAF cleaner)
• ICV-to-manifold gasket
• All secondary air pump hoses from the intake manifold through to the secondary air pump valve
• All PCV components, including separator, hoses, and gasket
• Intake boot, replaced with Mishimoto boot for ASC delete. ASC plug on the boot was filled with an aluminum plug from ECS Tuning.

Final result:


Unfortunately, it still runs rough, with the same problem. No other codes. Sometimes it runs fine, sometimes it doesn't; though for a smooth run it seems to "prefer" warmer weather.

Latest guess: sticking lifter on cylinder 1, since it seems to occur when cold. I'm currently running Redline 15w-50 as the engine oil. I'm going to try an oil change to 10w-40, Redline's recommended weight, to see if it makes a difference. But after this morning's behavior, where restarting the car 'fixed' the issue up through the rest of the drive, I'm wondering if I don't have a dying sensor.

So any ideas for this niggle? Thanks all!

[Driiven]

Best thing you can do is datalog this car. Check fuel trims. Also get your hands on an inpa cable or snap-on, autel, launch system and run the smoothness test to see where you at. Could just need a spark plug or fuel injector rebuild on cyl 1.

[Eidolon]

Yeah, agreed. That's what I've been thinking is my next step. I think some friends have an AutoEngenuity setup. Not sure it'll work for this car. I'll check around. Thank ya!

[ThreeD]

Other thing that can cause intermittent issues is the cam position sensor -- maybe you can pick it up on your scanner.

[notMpowered]

Swap your coil pack to another cylinder and see if the misfire follows it.
CPS is also a common problem, but it often throws its own code.

[Eidolon]

Realized I never updated this! Thanks for more suggestions, fellow addicts.

I did swap the coils on cylinders 1 and 2. It could be the CMPS or CKPS, but I'm not getting a unique code for them. It only ever throws a P0301.

Next thing on my list is to go ahead and throw some spark plugs at it. I have no idea how old the plugs in it are, and plugs are cheap. I plan to buy NGKs.

[Ex36]

This sounds kind of similar to a problem of my own I created on my Miata, and it's a bit of a long-shot. But I re-did the intake and with the after-market system it was possible to install the MAF backwards (which is impossible with the stock set-up). And guess what this dummy did? It made the car run poorly under moderate acceleration, like it had a miss. But it didn't throw a code. Just something easy to check.

[TostitoBandito]

I just had the same issue with cylinder 5 on my car. It was a bad coil. First thing I did was replace all the plugs since they needed it anyways. Then I swapped coils, the issue moved, and the bad coil was isolated and replaced.

[Eidolon]

Alright, so updating this... I have replaced the plugs with NGK BKR6Es. Didn't fix it. I have since then taken it to two separate mechanics, including one of the better shops in the Raleigh area (Bimmer Performance Center, a great shop that I cannot praise enough). Thus far, I still don't have a diagnosis! Whatever the bug, it's a tricky one. Both shops swapped injectors and coils. First shop boroscoped the cylinders. BPC performed a leakdown. Every test came back clean. Worse yet, the car would then run fine after the debug, making it hard to continue chasing down.

So I still don't have the problem clearly nailed down! When the car decides it wants to run, it runs like a top, though. I ran it at my first Tarheel BMW CCA HPDE at VIR the first weekend of this month. God, what a car. With the suspension mods and Nitto tires, it was positively sublime.