2007 Mini Cooper S with a bunch of mods. Rough idle just started one day out of the blue. I’ve replaced the VANOS solenoid and it still persists. The coil packs are good, and no CEL. Any ideas where to start? See video (volume up).

 

The PVC system had been modified well before the idling issue started. The PVC system is routed through a catch can to atmosphere - just in case that is brought up. Car ran fine with the system the way it sits currently.

 

How many miles on coils, plugs, air filter, HPFP? How does it drive off idle? Is idle same with engine hot/cold?

 

Unknown mileage on coils, but I just replaced one of them that I thought may have been a partial culprit with no change. Plugs are brand new. Air filter was just cleaned (Amsoil blue filter for the JCW intake box). HPFP was replaced in Dec of 2020. Off idle the engine is fine, except at freeway speeds when at WOT - sometimes it will hiccup briefly. Same idle issue whether hot or cold.

 

are you tuned? what are your "bunch o' mods"? how many miles does the car have? have you ever used injector cleaner? my car at 68k miles, stage 2 tune w/supporting mods, had a lumpy idle till i ran thru a couple treatments of rislone injector cleaner. i looked at my intake valves and they are clean, but I have a N18. when did you do your last valve blast?

 

Whew... where to start. P.O. rebuilt the motor at about 140K. Motor has 204K on it now. The rebuild consisted of all new bearings, CP stock sized pistons and compression ratio, and completely rebuilt head. According to the receipts, it looks like the injectors were cleaned and checked.

Stage 2 Mario tune with supporting mods, JMTC 42mm turbo (installed last month), 2 1/2” catless downpipe to 3” exhaust.

 

so thats 64k miles ago if my maths are correct. have you looked at your intake valves recently?

 

No. I’ll take a look this week.

These little cars a frustrating. I work on cars as a hobby, but I’m new to these. Most cars, I research the symptoms, and I can narrow down the problem pretty quick. These cars - name a symptom, and it’s a dozen different things that could be the issue. A CEL would be nice to point me in a direction, but it won’t throw a code.

 

i hear ya. carbon build up doesn't throw a code, hpfp doesn't necessarily throw a code even when it is affecting drivability. dealer will only diagnose via codes so they are mostly useless unless you got towed in there. these forums are a great help in knowing what possibly went wrong and what is going to go wrong. meanwhile, might as well drive it like you stole it :D

 

Truthfully, I drive the crap out of the car. For what I paid for it, I figure if it blows, I’m not out much. I’m just picky about my vehicles, and I like them to be running well. This car fights me.

I might go the R53 route. There are some reasonably priced ones in the area, and I’m reading they are easier to work on. If I do go that route, I need this one to be running well so I can sell it.

 

I think so long as you know what to expect you'll be okay. The N14's need more TLC, make sure you check your oil level frequently, since you are tuned change oil every 5k for cheap insurance. Read these forums for other N14 related items but at the mileage you're at they may have already been done.

 

I think I found the problem. Brand new NGK spark plug broke. Covered up the tip of the spark plug.




Took the intake manifold off. My valves are awful. Completely caked in carbon. I’ll be getting dirty today.





Hopefully, the combination of these two things help with the idle and overall performance. I’ll report back.

 

wow, fixing those 2 things will absolutely make a difference. how was that plug even firing? is that a NGK 1422 plug?

i re-read this post and you mentioned you vent PCV to atmosphere, where is all that carbon coming from?

 

I just rerouted the PVC system about a week ago. The P.O. just had the standard system in place, but as I got schooled up on DI engines - I thought I could try to avoid the build up as much as possible with the reroute.

Yes, 1422 NGK plugs - brand new. The inner part just came loose and was rattling around in there. I changed the coil pack on that cylinder bc I thought it was the culprit, not realizing it was the plug. At least I wasn’t going crazy. I think as it rattled, sometime the spark would actually ignite the fuel.

 

All done. It’s like a new car. Idle is smooth and even with or without the A/C on. I seriously thought it had stalled at a traffic light it was so quiet and smooth. Breaks the tires loose through first and second again!!! Glad I took the time to scrub the intake valves - what a pain in the butt. I cleaned one of the old plugs and reinstalled it. Put the old coil back in too.

Thanks for the input.

 

Glad to hear! Here is a thread with some good tips on maintaining a tuned gen 2 cooper:

Maintaing a tuned Gen II

I did notice this in particular about a catch can:
If you’re thinking of venting to atmosphere…don’t do it. A source of negative pressure is necessary to keep the crankcase from becoming pressurized. If the crankcase becomes pressurized the compression rings can float off the ring lands. When this happens, the rings do not seal as effectively which makes blowby even worse. In extreme cases the crankcase can become pressurized to the point that the engine develops oil leaks, oil flow back to the pan can be interrupted, and oil can even be blown out the dipstick.

Tips like this from knowledgeable members hopefully will prevent avoidable problems down the road. Motor on!