Mini Cooper R53 stuttering...

[S2r]

I've got a Sept 2004 Cooper (not an S) convertible with lots of miles on the clock and under load / partial throttle around 2-3000 RPM, I can feel it missing or stuttering very slightly, but not a full blown mis-fire. It's particularly noticeable going up a big hill round the corner.

I don't notice it when I bury my foot in the carpet at any revs so it may not be happening when I do that...

It was serviced about 5000 miles ago with new plugs and all filters and I've replaced the coil and leads in the last couple of weeks due to rusty connections yet the symptoms remain.

I've plugged it into my odb2 reader but it isn't throwing up any codes so I'm stumped.

Any ideas what to look for/change/fix next?

[E-bmw]

It is very common on these to have rust get into the HT connections on the coil pack causing what starts as a slight misfire.

Just pull the plug leads off & you will very easily see it if it is there, new coil pack sorts it if it is.

[GreenV8S]

Did the symptoms start before or after replacing the coils and leads?

[S2r]

GreenV8S said:

Did the symptoms start before or after replacing the coils and leads?

It started before I replaced the coil and leads - I found a rusty connector on the old one so thought that that must have been the problem, obviously not.

The more I think about it, the more it seems like it may have become slightly more pronounced since changing the coil and leads (or I may just be imagining that as I'm waiting for it to happen...)

[chrisch77]

It sounds silly, but have you checked the spark plugs are still tight? It is a known issue with plugs coming loose on the old Tritec engines - we blew a loose plug out on a Cooper S and had to have the head helicoiled.

Chris

[S2r]

chrisch77 said:

It sounds silly, but have you checked the spark plugs are still tight? It is a known issue with plugs coming loose on the old Tritec engines - we blew a loose plug out on a Cooper S and had to have the head helicoiled.

Chris

Not yet

I'm going to drop them out later and have a look at their colour as well.

[Mignon]

They're prone to burning out exhaust valves.

[GreenV8S]

If you've been running for a while with an intermittent ignition fault and not got things good and hot since then, it's possible you have got fouled plugs. Unless it's particularly difficult to do, it would be worth pulling them out for a check.

[S2r]

All of the plugs look the same, colour looks good so I've put them back in...

[S2r]

No change after a couple of weeks but I've found that it's more noticeable when everything is up to temperature - no problems (or significantly less) when cold - 50 mile trip up the dual carriageway, come to a big hill and it's all stuttery stuttery.

As it pulls alright higher up the rev range, I need to try and understand what's different below 3500/4000 rpm, as it feels like a fuel problem. Is it worth chucking a does of fuel system cleaner through it? Something like 'red line S1'?

[Coilspring]

Think you need fault codes and live data.

Is the temp sensor reading correctly would be the first check.