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      11-17-2015, 05:42 AM   #1
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DIY Fix your lumpy erratic idle with ease

Apologies if this has been posted before, or is a little too basic/obvious, but thought I'd share. I'm no mechanic but this is easily doable by even the most ham-fisted ape:

Background
I've recently purchased an F10 M5 with circa 30k miles. Car is fantastic but now I'm getting used to it I became a little frustrated by a lumpy idle. Nothing dramatic (and no warnings on the dash) but irritated that the rev counter just couldn't settle when sat in traffic. It was no more than a 100/200 revs wobble but enough to irritate.

Investigation
Searching the net (and remembering from when I owned an E46 M3) I was fairly certain the cause would be one (or both) of the MAF (Mass Air Flow) sensors. Since there were no alarms I assumed they were just dirty, not knackered. I considered just running it down to BMW but I'm out of warranty and thought it was worth having a fiddle first.

What you'll need
1. Torx bits
2. MAF cleaner (and only MAF cleaner - no other cleaner will do). Liqui Moly have a good one on Amazon: http://www.amazon.co.uk/30/dp/B00295EEBK
3. Lots of lint-free paper towel
4. Literally nothing else

Solution (and steps)
1. Open the bonnet, making sure the engine and ignition are off
2. Locate the MAFs (they're a doddle to find - they're on the big black pipe leading from the airbox to the engine, between the airbox and the flexible section of pipe, just before the jubilee clip. They have a cable running to them. One on each side of the engine. (here's someone else's picture - it's where the green circles are - ignore the red ones: http://f10.m5post.com/forums/attachment.php?attach...
3. The cable should be easy to unclip so don't force it. If it doesn't come away easily then the security lock is applied. If that's the case, don't worry - you can either fiddle with the security lock or just clean them with the cable still attached.
4. Use a torx to undo the two screws holding the MAF in place (careful, they're easy to drop and will never be found again). Put them somewhere safe.
5. Pull the MAF out of it's hole in the air intake. If still connected to the cable then rest safely on the engine or airbox, if not then remove somewhere safe for cleaning.
6. Get your can of MAF cleaner and spray that stuff in all the holes of your MAF, paying particular attention to the metallic looking bits (after all, they're the bits you're actually trying to clean).
7. WARNING: You'll be using the force of the MAF cleaner (and it's solvents) to clean the MAF. So, there's going to be LOTS of overspray. If you've removed your MAFs completely then no bother. If you're doing it in the engine bay then use LOTS of paper towels to cover everything first.
8. Spray like crazy. Spray every little spec of crud or film or whatever out of your MAF. You may want to do this a bunch of times until the metallic parts look brand new.
9. WARNING: Don't be tempted to touch any of the metallic parts, even with a cotton bud. If there's persistent crud then use more spray. It's not like you're going to need that can again for another 30k miles is it?
9. Leave the MAF somewhere very safe to air dry (turning occasionally). Takes about 15 minutes depending on the temperature - but the MAF cleaner evaporates pretty quickly. (probably the ideal time to make a brew)
10. Refit the MAF (steps 3, 4 & 5 in reverse) remembering to reconnect the cable if you disconnected.
11. Check the car starts okay and doesn't throw any alarms.
12. Do the other MAF on the other side of the engine
13. Start the car, again checking for any alarms. Take it for a blast!
14. Sit back, admire your lovely smooth idle and probably improved MPG too (also, enjoy knowing your two MAFs should last a lot longer and you've saved yourself 500 for replacements further down the line).

Hope this helps someone!
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      01-31-2016, 12:52 AM   #2
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Awesome!! I'm going to give this a shot. I have the same idle issue. It's not enough for anyone to notice but enough to bother me when at the light.
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      02-04-2016, 07:36 AM   #3
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Quote:
Originally Posted by 13M5F10 View Post
Awesome!! I'm going to give this a shot. I have the same idle issue. It's not enough for anyone to notice but enough to bother me when at the light.
Great! Glad someone found it useful. Let me know how you get on
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