still doing a rough idle!!! what is going on??!?!?@

[Jover]

my MCS is having a rough idle again, after replacing coilpack, wires, plugs with factory OEM the rough idle disappeared, but then suddenly a couple of weeks later the rough idle came back. so im guessing that replacement of wires,coilpack,plugs did not fix the problem. What could it be? It makes a loud churning sound, i could feel the whole car vibrate like its going to cut off...then about 15-20 seconds it levels back up to normal idle/rpm. please share your opinions

[N2MINI]

Has the check engine light ever come on?? You probably did this as you were replacing your igntion stuff but if not try disconnecting the negative battery terminal for a few minutes and then reconnect to let the OCU reset... Also might have a sensor of some sort going bad..

[BlimeyCabrio]

Things to check:
1) as Bryan said - any CEL / SES light? if so, read codes
2) fuel? unlikely as it sounds like it's been going on for a while. But if you always use the same source, try a different one
3) air filter - dirty one can cause rough idle
4) other vacuum hoses - there are several - make sure all are connected. vacuum problems are notorious for stuff like this.
5) fuel pressure regulator - it's under the intercooler, attached to the fuel rail. It has a tiny vacuum hose that connects it to a nipple on the intake manifold. If either end pops off, unusual things can happen, and sometimes it won't throw a code.
6) fuel filter - most MINIs are still on the original factory filter (inside the fuel tank, accessed under the back seat, a mess and a pain. In my experience, these get nasty after about 50-80k miles. If nasty enough, they can cause fuel pressure issues.

[Jover]

No code at all
Fuel filter replaced about 3 months ago.
which sensor could it be? but no engine light came on, so it cant be the sensor right?

[BlimeyCabrio]

Dirty MAP sensors can cause idle issues - probably don't need to replace them (they almost never fail), but they may be dirty. Remove, use MAP sensor cleaner or electrical parts cleaner (not other stuff) and reinstall.

Another possible culprit are leaky rubber intercooler boots.

Anything that causes the car to get more (or less) air (or fuel) than it should at a given RPM and load are potential causes.

Every time I've had idle problems, it's come down to plug wire contacts, or vacuum on intake tract leak somewhere.