Rough running, no codes yet

[exodus454]

Hoping maybe someone can give me a little help with diagnosing a problem on my m3.

Lately it's been driving "roughly", not necessarily a misfire but something's definitely up. Idle and light cruising aren't really affected but as soon as you lay into it any further it starts getting more rough and definitely seems down on power.

It's done similar things in the past and it's been coilpacks or TPS, but it just got a fresh set and the problem persists.

No CELs, EMLs, looking at all the sensors nothing looks out of place.

Oil and coolant look normal.

Air filter looks normal, it's probably 4 months old but definitely not plugged solid

Nothing sounds out place like it kicked a shim or timing chain noise, no strange leaks, smoke, the VANOS adaptations haven't moved.

I've tried logging the problem with testo and during the roughness nothing indicates a problem, no timing fluctuating, VANOS movement looks normal, throttle movements looks normal

Compression is 180 with no noteworthy detlta

Fuel pressure is 72psi, drops to 64 psi at idle
Note: With the test gauge installed after the regulator reading 72psi, if you close the valve (effectively isolating the front half) the injectors bleed down to 10psi within 20mins

Fuel filter is 2 months old

Smoke tested intake and exhaust for leaks, none currently

Spark plugs are 3 months old, NGK iridium, none of them show damage or strange color, they're all fairly consistent

Both the engine side TPS are new, also swapped out the gas pedal with a known good one and no changes


The only actual hard evidence I've been able to come across is the uneven running in INPA, nothing actually registers as a "misfire": screenshot attached

After that I tried swapped the 1/2 injectors and the cylinder 2 stayed as the worst, no real change.

I'm still leaning toward it's just time for injectors (to my knowledge there original with 200k) but I really hate just throwing money at it.

Any ideas?

Its a 2005 with 195k on it right now, it's running the CSL software with map sensor. I have a wideband and there's definitely rich spots, it feels similar to a rich misfire, but even it does it in the leaner spots too so that theory doesn't seem to pan out.

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[JeremyJames]

I feel like you have done a pretty damn good job troubleshooting thus far. I think you’re on to something about the injectors. Recently I had my ITB rail off and I was going to replace injectors as a preventative, but they were on BO. Not sure if they’re back in stock now, this was for Genuine BMW. I wouldn’t send them off to get flow tested and cleaned because I’ve heard a mixture of stories with that process, unless you’re able to find a shop you have confidence in.

[exodus454]

Thanks, it's been my experience with this car anyway that there's always an answer somewhere!

I was looking recently at injectors and it looks like BMW are somewhat easy available, Bosch not to much. I'm not spending whatever ludicrous price BMW sets, I'm super hesitant to get them rebuilt or buy reman ones. I haven't had a bad experience but I've seen it first hand.

If the Bosch aren't easily available I'm inclined to just find different set that will work that aren't necessarily M3 specific.

I'm just amazed it runs like it does and the DME is happy as a clam.

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[Tbonem3]

Camshaft position sensors.

[exodus454]

Camshaft position sensors.

Thought did cross my mind, the set that's in there has probably 60k on them. I do recall it behaving similarly when the last set went. I'll get another set on the way from FCP, definitely worth a shot (especially for free!)

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[Tbonem3]

Ah, if they've already been replaced once before, it's probably something else then. I assumed they were original. They can go bad intermittently, and not throw codes.

[exodus454]

Ah, if they've already been replaced once before, it's probably something else then. I assumed they were original. They can go bad intermittently, and not throw codes.

They were replaced already, the crank sensor was replaced recently too.

I think the only one that hasn't been is the CTS and the injectors

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[TexaZ3]

Fuel/injectors/vanos solenoids. I'd start checking those.

[exodus454]

Fuel/injectors/vanos solenoids. I'd start checking those.

What do think the likelihood is it's a solenoid issue? If anything under 3k, idle and cold start are all really unaffected

The PO did the VANOS stuff from that before I bought it @ 100k

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[exodus454]

So I think we have a culprit! Was driving yesterday and got a slew of CEL/EMLs, soft limp all the time and DSC/brake (hard limp) whenever I'd touch the throttle.

Scanned it and it had 7 different throttle related codes, so I started swapping the easy TPS with no change. So then I pulled the manifold off to swap the other one with no change also.

At this point it after clearing all the codes, the only one that would come back was throttle self-test, so I started looking around more carefully and noticed the first two throttle blades weren't moving!

Their pushrods popped off the balls! I'm guessing the chain of events was the second one popped off initially causing my rough running, then by dumb luck the first one followed which stopped transmitting the angle position to the top TPS = CEL/EML/hard limp immediately.

I have a new set on the way, my gut says this is the problem. I'm pretty sure I won't get new ones and it still drives like it did. I guess these should absolutely be on the list of stupid high-mileage parts that should be replaced.

I wish there were easily sourced metal links, the ABS plastic is pretty cheap. I'd be surprised if worn plastic ones didn't effect the throttle balance, especially at low throttle angles.

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