I have what seems like a semi-typical "rough idle" problem: when the engine is cold/cool, it idles fine, after it warms up, it idles like 1 or 2 cylinders aren't firing...my codes are generally, "cylinder X misfire", "multiple cylinder misfire". Cold or warm, the engine power feels fine...sometimes I get a puff of blue smoke after idling at a stoplight, sometimes I don't.

Possible issues, none of which (apparently) apply to me: plugs, coils, oil level, VANOS valves.

I've just ordered a pair of vanos return valves and will try that next, (and hopefully that will fix it).

But OK...here's the twist that has become apparent to me after driving with this issue for a couple years:

1) The check engine light will chime quite often (every few seconds?) when I am going down a slight grade, in gear, with light pedal pressure (typically at highway speeds)....there's something about that condition that makes the "misfire" code really get active. If I have NO pedal pressure, the chime stays silent...mostly.

2) When I come to a stop after that downhill condition, the idle is REALLY bad...and more than that, when I try to accelerate, the engine has decreased power and sounds like it is missing...or...the engine is running more or less fine (no missing), but feels like the variable valve timing is not working (my gut instinct)...what I mean is there is maybe 50-75% power...there's no "zip".

So OK...

My question is...what is happening in the engine (oil flows, air flows, etc), during that in-gear, downhill, light-pedal condition, that makes the misfire and rough idle problem so much worse? I feel like if someone could figure THAT out, we might very well know the exact cause of the warm-engine-rough-idle issue.

Thanks...

 

I had similar cold rough idling symptoms. Had a CEL, but ran better when warm. Turned out to be a failing O2 sensor.

Suggest you get car to someone with equipment to review ECU data. Could be a lot of things (HPFP, bad coils, etc.) If car has over 100K miles, I'd suggest replacing spark plugs and coils.

Good luck,

W

 

What are the codes?

 

W...

Thanks for that...yeah I've been thru all that...very experienced MINI mechanics (both dealerships and smaller shops) all try the most obvious first (which is appropriate of course)...new plugs, swap the coils...then they throw their hands in the air and can't figure it out. There are many other folks on NAM that have this same problem.

--

Bill

 

"Cylinder X misfire" (always cyl 1, sometimes 2, never 3, rarely 4)
"Multiple cylinder misfire"

If I recall (don't have the car with me right now)...

P0402 (and others closely related)

"Misfire" seems to be a simple word to you and me...it sounds like it means a plug didn't, well, "fire" (ignite)...because the plug itself or it's coil is bad...but it's way more complicated than that...the sensor (according to an experienced MINI mechanic) is simply watching the rotation of the engine...if the rotation "stumbles" at a particular position of it's rotation, then it uses that position to INFER which cylinder(s) "misfired".

In reality, the sensor has NO IDEA what caused the stumble...plugs, coil, or a whole host of other things that could make the engine's rotation stumble.

In my case, whatever IS causing the stumbling might indeed happen when cylinder X should have fired...but it's not the plugs or coils. Based on research and experience, I think it has something to do with the intake and exhaust valves (probably the variable valve timing operation)...hence the reason so many people try to replace/clean the VANOS valves as the 3rd or 4th thing they try (after plugs and coils).

Anyway it's a big mystery...I'll have the vanos return valves (not the vanos valves) replaced about the end of February, and will report back...unless someone knows a different/better solution in the meantime.

--

Bill



--

Bill

 

 

The puff of blue smoke is an oil consumption tell-tale. Oil in the air/fuel mix reduces the effective octane rating. This can lead to pinging/detonation that might be below the audible threshold but enough to trigger the knock sensors. This in turn results in retarded ignition timing and reduced performance. A long coast down followed by an erratic idle would have me looking at oil in the intake tract. I would then look closely at the crankcase ventilation system.