Had a bit of a day in the sunshine today, giving the M3 some attention. I've wanted to remove the intake system and give it all a clean for ages, but have been too afraid too/not had enough time/not had good enough weather. So finally today I was feeling brave, I had time, the sun was out. Took the plenum off and gave it a clean, along with the idle control valve and the throttle bodies. I also put a new throttle position sensor in under the plenum whilst I had it all in bits. All in all, quite an easy job. The only thing which is a PITA is redoing those circlips on the throttle bodies. Eventually though I figured out how to do them and like anything on cars, it's knowing how it do it properly and knowing the tricks of doing it which allow you to finish the job quickly. Now I think I could take off the plenum and replace it in about 30 minutes.
For anyone interested here's a 30 second step by step.
- Remove strut brace (4 x 13mm)
- Remove cabin filter and cabin filter housing (3 turn clips, followed by 4 Torx T....30? screws)
- Remove top PCV hose
- Remove air intake system (remove xenon ballast cover and a couple of nuts, loosen some jubliee clips and pull stuff out) and unclip MAF sensor.
- Undo the chrome 10mm screw holding the dipstick on
- Undo the two 10mm nuts holding the plenum to the bracket underneath (I recommend using a ratchet combination spanner, preferably with a flex head)
- Use some pliers to squeeze a hose near the front and wiggle it out.
- Undo a few misc connectors that might be hanging around (battery cable and hose that runs to the back of the plenum and another one off the bottom of the plenum that just pushes off a flat bracket)
- Unclip all 6 of the circlips holding the plenum to the throttle bodies.
- Grab the side of the plenum (the big oval hole) and repeatedly rock/pull upwards and away from the throttle bodies.
- The small hose that runs to the sump should just fall off as you lift it out.
It sounds like a lot, but in reality it isn't. You're just unclipping anything you see connected to the plenum. Oh and if you take the hoses of the ICV (ICV underneath TB 2), you won't be able to get them back on. They aren't like the other circlips there is nowhere to allow you to squeeze them back on. I had to substitute them with two jubliee clips in the end.