My car (M635csi) had a poor cold idle -500rpm and when hot would only idle at 650rpm.

The main bleed valve was OK (The big one under the air box). TPS switch OK. Plugs OK, wires OK etc. After checking all these I was led down to the throttle bodies. Removed the air box and looked at throttles plates to ensure they were all closed (as they should be)for idle. Then I looked at the small bleed holes which go to the bleed valve to bypass the throttle plate. These were very badly blocked with black goey crap. To remove the bleed valves is a bit tricky but this is how I did it.

Unscrew bleed valve recording the number of revolutions so that the valves can be replaced to the same set point - not an exact science but it worked for me. Then remove crap with ear duffs - there was a hell of lot of crap - the wife was not impressed as I used a whole box of ear duffs to clean all six. Clean the bleed valves as well. Replace valves to set position replace air box and run the engine. The bleed valves are used for PRECISE air flow to the cylinders for idle. My idle speed when warm is now 950 rpm with no missing spluttering etc. I also checked the vacuum on each cylinder at idle - with a normal vacuum guage fitted ot the vacuum pipes on each throttle. At idle the gauge will flicker but should deflect into the idle region of the scale on the gauge. I did this for all six and set the bleed valves to give the same vacuum. Some one had messed with my bleed valves previously. Job took about 2 hours plus some fiddling to get the idle speed correct. Idle speed can be increased (for a warm idle) by letting a little more air in for each cylinder. I turned each bleed screw open by one quarter revolution until I was happy with the idle speed.

One of the most pleasing jobs done yet on the car as the drivability from idle and gearchanging have vastly improved.

Best of luck
If you require more let me know

Ian

Can you provide a little more information about this? Is there a procedure anywhere? How much stuff did you have to remove to get to these things? Any other tips?

I would have a look at the air bleed valves around each throttle plate. If these are blocked then it can create the sympthoms you describe as the cold start up will get it's air from the main bleed valve(under the air box) but when this closes with the engine heating up their may be insufficient air supply through the individual bleed valves. Mine were in a terrible state (154k miles)and hot idel was vastly improved following the cleaning of the bleeb valves and associated channels

Best of luck

Ian