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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Tue, Jul-17-2018, 10:13:14 PM   #11
mrgizmo04
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Default Re: Idle jumps up and down after hot restart

The point I was coming from...
If the car starts fine and runs fine from cold but then has an issue after it warms up, with warm/hot restart, it is heat soaking and dependent on temperature (underhood temps actually rise after you shut the car off and stay elevated for 30mins or more).

When car is started from cold, it runs in open loop, depending on maf and coolant temp to get appropriate amount of fuel to run. After it warms up, it goes into closed loop, depending on o2 sensors to get the amount of fuel to run. When I say fuel, I mean afr.

Check your maf by simply unplugging it when it starts bouncing/hesitating to see if it smoothes out, it will tell you if it is causing the issue. The intake air temp sensor is in the maf.



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Old Tue, Jul-17-2018, 11:29:39 PM   #12
Texaz3
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Default Re: Idle jumps up and down after hot restart

Quote:
Originally Posted by mrgizmo04 View Post
The point I was coming from...
If the car starts fine and runs fine from cold but then has an issue after it warms up, with warm/hot restart, it is heat soaking and dependent on temperature (underhood temps actually rise after you shut the car off and stay elevated for 30mins or more).

When car is started from cold, it runs in open loop, depending on maf and coolant temp to get appropriate amount of fuel to run. After it warms up, it goes into closed loop, depending on o2 sensors to get the amount of fuel to run. When I say fuel, I mean afr.

Check your maf by simply unplugging it when it starts bouncing/hesitating to see if it smoothes out, it will tell you if it is causing the issue. The intake air temp sensor is in the maf.



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Thanks, that's a good diagnostic approach.
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Old Wed, Jul-18-2018, 02:28:36 AM   #13
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Default Re: Idle jumps up and down after hot restart

I noticed this last night on my M3, it was driven for about an hour then was parked at a restaurant, upon restarting the idle went up/down for about 10 seconds. However mine didn't jump more than say 100 rpm. Guess this is something I need to look into then? I am VERY new to BMW's...
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Old Wed, Jul-18-2018, 04:18:53 AM   #14
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Default Re: Idle jumps up and down after hot restart

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I noticed this last night on my M3, it was driven for about an hour then was parked at a restaurant, upon restarting the idle went up/down for about 10 seconds. However mine didn't jump more than say 100 rpm. Guess this is something I need to look into then? I am VERY new to BMW's...
Light fluctuations are normal. Unless this becomes noticeable, like when you say to yourself "WTF is that?" I wouldn't worry too much. I'll try to catch it and post a video so you could compare. Mine are pretty noticeable. But I have not had it since I started this thread, very intermittent.
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Old Wed, Jul-18-2018, 01:47:47 PM   #15
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Default Re: Idle jumps up and down after hot restart

Curious to see a video Texaz3. I'll try to get one of my issue as well, but also very intermittent. Sometimes it'll happen once a day, other times it can go for months without a hiccup. It definitely is temperature dependent, but nothing as reliable as saying "a hot day and a warm engine will guarantee a jumping idle"
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Old Wed, Jul-18-2018, 02:42:50 PM   #16
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Default Re: Idle jumps up and down after hot restart

New maf needed. Idle hunting is not normal. Even with no codes, ur maf can and would be not as true and accurate as it once were.
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Old Wed, Jul-18-2018, 04:33:06 PM   #17
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Default Re: Idle jumps up and down after hot restart

I use to think it was my timing. Like it's looking for the right rhythm. But I do need to change/ clean my maf, as well as my throttle sensors. So wether cold start or warm start, it shouldn't hunt?

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Old Wed, Jul-18-2018, 07:23:52 PM   #18
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Default Re: Idle jumps up and down after hot restart

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Originally Posted by andrewrivera141 View Post
I use to think it was my timing. Like it's looking for the right rhythm. But I do need to change/ clean my maf, as well as my throttle sensors. So wether cold start or warm start, it shouldn't hunt?

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Of course not
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368.4 whp 289.1 wtq

Custom exhaust thread and dyno http://m3forum.net/m3forum/showthread.php?t=569086
Cams thread and dyno http://m3forum.net/m3forum/showthread.php?t=554439
Custom cf airbox thread http://m3forum.net/m3forum/showthread.php?t=595180
Why not to use after market bearings with surfacetreatments and /or increased clearance
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Old Wed, Jul-18-2018, 08:29:44 PM   #19
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Default Re: Idle jumps up and down after hot restart

No, technically it shouldn't, but due to various reasons, one big one being the age of these cars and many little things that go out of whack over time, many cars do. As long as it is intermittent and does settle quickly, I wouldn't worry about it.
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Old Wed, Jul-18-2018, 09:14:12 PM   #20
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Default Re: Idle jumps up and down after hot restart

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Originally Posted by Texaz3 View Post
No, technically it shouldn't, but due to various reasons, one big one being the age of these cars and many little things that go out of whack over time, many cars do. As long as it is intermittent and does settle quickly, I wouldn't worry about it.
If it hunts,it aint running right. Your maf would be on its way out more likely than not. If no vaccum leaks and icv is ok, then its ur maf , no ifs buts or maybes about it
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-Custom dyno tune
-Tms pulleys and electric fan conversion
368.4 whp 289.1 wtq

Custom exhaust thread and dyno http://m3forum.net/m3forum/showthread.php?t=569086
Cams thread and dyno http://m3forum.net/m3forum/showthread.php?t=554439
Custom cf airbox thread http://m3forum.net/m3forum/showthread.php?t=595180
Why not to use after market bearings with surfacetreatments and /or increased clearance
http://www.m3forum.net/m3forum/showp...4&postcount=10
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Discussing Idle jumps up and down after hot restart in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)