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      01-08-2022, 11:19 PM   #1
M5_Raz
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How To Fix Surging Idle On F10 M5 & S63TU Engines

Hey Guys,

Over the past 6 months my idle when first starting the car in the morning was surging by a couple hundred rpm usually and even up to 500 rpm on colder days.

I was thinking that it must be the cold start delete acting up. However I remembered reading about cleaning the MAF sensors and it helping.

It's super easy. Each air intake has one that's being held in by two screws.

I first unplugged the sensor. You wanna pull the little grey tab first, then while holding that down, you can unplug it. Next you can remove the two screws.
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Once that's complete, you can pull out the sensor. As you can see, mine was very dirty with oil.
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I used CRC Mass Air Flow Sensor Cleaner to clean it.
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All you have to do is hold the sensor and spray it, don't wipe or touch it. I used quite a bit to get everything off. Here is the difference between a clean one and a dirty one.
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The car is MUCH smoother now. Cold starts have no more problems and even driving it is so much better, especially when the oil is still cold. I definitely feel more power in the lower end too.

Took me 20 mins in total. Just filled it up and will report back with any MPG improvements, if any. Thanks!
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      01-09-2022, 11:15 AM   #2
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Looks better. Do you have stock air filters or oiled aftermarket ones? Thanks!
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      01-09-2022, 11:24 AM   #3
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Great write up , I will do this next week.
Thanks
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      01-09-2022, 12:20 PM   #4
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Quote:
Originally Posted by ECB View Post
Looks better. Do you have stock air filters or oiled aftermarket ones? Thanks!
Thanks! Stock air boxes and filters with the charcoal filter removed.
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      02-01-2022, 02:13 PM   #5
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I ordered a pair of new sensors from FCP Euro and just use the lifetime warranty to swap on regular intervals.
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      02-05-2022, 10:53 AM   #6
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Quote:
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I ordered a pair of new sensors from FCP Euro and just use the lifetime warranty to swap on regular intervals.
That's a good idea too. But it's more work and initial investment. How often do you change them?
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      02-05-2022, 10:59 AM   #7
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Just wanted to report back for anyone that is curious. Drove about 1000 miles and I have noticed slight mpg gains, nothing too drastic to really make a difference (~0.5mpg). The car is still smooth at idle.

For 30 min and a few bucks, I recommend everyone to do it. Thanks!
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      02-05-2022, 06:57 PM   #8
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Quote:
Originally Posted by M5_Raz View Post
That's a good idea too. But it's more work and initial investment. How often do you change them?
So far I have only swapped them twice. I didn't check the mileage but was just over 12 months and really only did it because I was replacing coils.
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      02-22-2022, 10:47 AM   #9
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Do that every 8 or so months on mine though have no oil spray on them yo
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      05-17-2022, 11:00 AM   #10
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hope it will fix my problem with idle
also had cold start removed (was blaming on it but will check this week)
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      05-17-2022, 03:45 PM   #11
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Quote:
Originally Posted by BBHMM View Post
hope it will fix my problem with idle
also had cold start removed (was blaming on it but will check this week)
Yep, same thing happened with mine. Catless and cold start removed.
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      05-17-2022, 05:33 PM   #12
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Quote:
Originally Posted by M5_Raz View Post
Quote:
Originally Posted by BBHMM View Post
hope it will fix my problem with idle
also had cold start removed (was blaming on it but will check this week)
Yep, same thing happened with mine. Catless and cold start removed.
Quote:
Originally Posted by M5_Raz View Post
Quote:
Originally Posted by BBHMM View Post
hope it will fix my problem with idle
also had cold start removed (was blaming on it but will check this week)
Yep, same thing happened with mine. Catless and cold start removed.
Damm in my case it worsen the problem I guess have to buy 2 new sensors
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      05-17-2022, 06:04 PM   #13
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Did you wait for them to dry?
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      05-18-2022, 10:45 PM   #14
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Quote:
Originally Posted by M5_Raz View Post
Did you wait for them to dry?
Quote:
Originally Posted by M5_Raz View Post
Did you wait for them to dry?
Yes but I sprayed aloooot ) maybe that was my problem, also got check engine today (error code 102002), anyways Friday will know how good it runs with new sensors
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      06-15-2022, 02:13 PM   #15
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So far cold start is tuned back ON , new MAF sensors2x, litle surge, but now after car warm up no idle problem at all
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      03-29-2023, 08:31 PM   #16
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Thanks for the DIY Raz. $10 and 30 mins later, and my idle is buttery smooth again.
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