Suddenly my 2003 MCS started to idle very poorly, it hunts up and down between 1000 and 2000 RPM acceleration from stationary is rough and I have to put my foot harder on the accelerator to compensate, also MPG has dropped about 10%. can anyone help.

 

Start with the basics, check plugs, replace as needed. Air filter...all the usual suspects.

 

replaced plugs and air filer about 3 months ago runs fine after initial acceleration no misfire.

 

I would check in this order:

Vac leak
coil pack
plug wires
MAP Sensor
Fuel pump - Mechanic can check for pressure at the rail. Dealer can check percentages of how often the ECU makes fuel value corrections.
Fuel Pressure Regulator - Also has two O-rings.
Fuel Injector O-rings - cracked/hardened - poor seal
Poor ground strap connection

Also, if you have not already, for 20 bucks I would replace the PCV valve. It would be at the top of this list too and should be replaced every 30K miles. Only available at MINI as it has it's own built in bracket.

 

Thank you, actually I just replaced the PCV valve about 10 minutes before reading this, (I had already bought a spare a few months ago), Where would I check for vacuum leaks? do you mean the ground strap from the engine to chassis? Is it worth buying a fault code reader?

 

lol, nice.

Yes, you will not always have a check engine light for certain codes. Some can only be read by the dealer too.

I would check for vac leaks in all the usual places. There are about half dozen or so problematic areas.

If you can swap coil packs/wires with another MINI owner that will help to isolate other solutions.

The ground strap on the pass side yes. Sometimes the strap is bad, and sometimes it's just a matter of cleaning the area with wire brush and rebolting it up. Best to use a 1/8th driver for those nuts too. A 3/8's or 1/2 inch drive is too much. The cast metal in that area is not that strong and you don't want to snap it off.....

Ground straps are cheap. Almost 100K miles on my S, so I am changing mine soon enough.

Two other possibilties is the Electronically controlled throttlebody....but would only consider that if you had some mileage on the car, and an O2 sensor. An O2 sensor code would come up on a Scanguage II btw.

 

Its got much, worse, it now surging between 1000rpm and 2000rpm in constant rhythm, but with A/C on not so much, how do I check for vac leaks... listen for hissing or spraying on some oil to see if it cures the problem? I'm getting a coil pack and leads sent to me to try and will work down your list, thanks.

 

i know this is a first gen forum but i have a 08 cooper s with very similar problems. If and when you find what was wrong with your car could you share it.

 

The engine idling at 2000 rpm problem was caused by a leak in the boost section ie a leaking boot on the intercooler.

 

Is the leak at the gaskets between the horns (left and right of the IC) and the IC?

 

Yes the rubber had pulled out of the clamp on the bottom, the left of the IC

 

I am bumping this thread because I am experiencing the same thing.

My idle is only rough when the car is cold. Then, I experience rough acceleration and excess vibration when on the throttle. If I put my foot on the clutch, the excess vibration goes away completely. If I rev the engine in neutral, there is no excess vibration or issue.

I did replace engine mounts, and I know that I should expect additional NVH, but I really think this is something separate from that and is just a coincidence. Some suggest vacuum leaks and I did order some new IC boots. I noticed a couple of interesting suggestions in this thread, most notably the ground strap connection. I did have to remove the ground strap to do the upper motor mount swap. I reconnected it, but could this be the source of my problem? Any other suggestions?

Grey Raven mentioned several common areas for vacuum leaks. Is there a thread detailing these?

 

I guess the bushings are filled with liquid. Remember that bubble gum, and there was some kind of pink goo inside? That's what I'm picturing.

 

 

haha no I'm not... that dumb forum feature where it starts loading a new thread at the bottom ><