my car just redefined 'lumpy idle'

my car has always had the typical M30 idle (smooth, then a little blip and then smooth again). last year it got worse though, i was sitting in the car idling for a few mins while my girlfriend grabbed something from the corner store, and it started to run rough.. i've had my mechanic look at it numerous times but he insists it's fine. i've got used to it so it doesn't bother me anymore.. it's just a slight rumble but nothing major.

but last night i let my tank run down to 20km range (i kept forgetting!) and then filled it up (premium, i've got an EAT). started it back up again and it was ROUGH. it feels like there are stones in the engine, the whole car rocks and the engine thumps.. so i started to drive home and it was smooth as silk. stop at a stop sign and it starts to rumble away again.

i drove it to work this morning and it was ok for the first few mins, then it started again. it is pretty severe, i'll get a video of it tonight. it's fine off idle.. no improvement in park or neutral.

any ideas what this could be? engine mounts? low compression? the ICV is only 6 months old..

this car knows when i've got a bit of spare cash!

At least you have experienced a smooth idle. I am still searching...

Sounds like the junk at the bottom of the fuel tank were stirred up and some of the small particles got by the fuel filter and has now gunked up the injectors. Drive it for a while, and if it don't improve try injector cleaner.

Same thing happened to me with my e30 M3 when I ran the tank too low. But it cleared up after few days.

evap purge valve stuck open?

I would do the basic maintenance items like plugs/ wired and the such, then advance to the fuel filter(s) etc... after you do the plugs and stuff remember to do a computer reboot.

Are you getting any codes from the stomp test?

gas made it bad eh...

fuel pump relay? (get a new one)

vacuum leak? (would wreck havoc with idle)

charcoal canister? (get a new one)

dirt in new ICV? (just clean it out)

dirty valves?

I'm no genius, but how about the Shogun reset? Before you go spending money, it's free innit.

I'm going to pick engine mounts for 500 dollars.

thanks for the suggestions everyone. unfortunately a rough idle was only the beginning. i jumped in this evening to leave work and *bing* coolant level. so i called a friend and he came out to rescue me with a couple of bottles of distilled water..

but.. it still wasn't finished with me.. i filled it up, turned the key and heard a sound that would make you all feel sick.. it kinda sounded like the leg of a large animal snapping.. it came from deep within the engine and left us both standing there staring into the engine bay in silence...

i didn't dare start it again although i'd say the major damage has now been done.

i will get it towed on monday to my mechanic, and will probably leave it there as some sort of display, $2 entry... 'come and see the red beast of terror, hold your wallets tight!'

Ouch, that sucks. Hopefully it sounds worse than it is.

Uh Oh!!..... Blown head gasket or cracked head?

I just hope that noise wasn't a rod snapping as the engine tried to compress raw water.....

If it's toast speak to Roger at the Beemer motor workshop in Maddington (he may be your saviour!)

Ross