Revs high then stumbles upon start; hpfp?

MountainStone · 05-19-2014, 10:47 PM

Every second or third cold start, my car will rev up to 2k or so then drop into a protracted stumble lasting five to ten seconds before settling into a normal idle. I am not experiencing extended cranks, just the weird rev-then-stumble. Is this a symptom of a failing high pressure fuel pump?

If not, does anybody have any ideas what it could be? I have a jb4 running map 1 (stock otherwise) but this is a recent development and I've been running the jb4 since December.

Thanx!

Give_Em_The_DD · 05-19-2014, 11:15 PM

Could be a few things. "Stumbling" as it goes to idle could be: plugs, coils, injectors, carbon buildup, hpf...

MountainStone · 05-20-2014, 08:12 PM

Quote:

Originally Posted by Give_Em_The_DD

Could be a few things. "Stumbling" as it goes to idle could be: plugs, coils, injectors, carbon buildup, hpf...

Thank you for the response. I'm surprised at the lack of opinions here. When I installed my JB4 it threw a code, so I changed the plugs and haven't had any codes since. This makes me think the plugs, coils and injectors are all good. To my knowledge my car has never had the carbon removed, but there are no other symptoms of carbon buildup. I'm puzzled at this odd idle situation...

e92_enthusiast_1 · 05-20-2014, 08:55 PM

After a tune I've heard that besides plugs, coils and injectors will degrade a lot sooner than normal so don't discount it just cause you did the plugs. Have you pulled codes?

05-19-2014, 10:47 PM	#1
MountainStone Private First Class 23 Rep 105 Posts Drives: 08 335i Sedan Join Date: Sep 2010 Location: Tejas iTrader: (0)	Revs high then stumbles upon start; hpfp? Every second or third cold start, my car will rev up to 2k or so then drop into a protracted stumble lasting five to ten seconds before settling into a normal idle. I am not experiencing extended cranks, just the weird rev-then-stumble. Is this a symptom of a failing high pressure fuel pump? If not, does anybody have any ideas what it could be? I have a jb4 running map 1 (stock otherwise) but this is a recent development and I've been running the jb4 since December. Thanx! __________________
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05-19-2014, 11:15 PM	#2
Give_Em_The_DD Banned 258 Rep 1,084 Posts Drives: 2010 black 335xi coupe Join Date: Sep 2013 Location: IL iTrader: (2)	Could be a few things. "Stumbling" as it goes to idle could be: plugs, coils, injectors, carbon buildup, hpf...
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05-20-2014, 08:55 PM	#4
e92_enthusiast_1 Lieutenant Colonel 35 Rep 1,652 Posts Drives: '10 AW/CR e92 6mt 335i Join Date: Mar 2012 Location: Chandler, AZ iTrader: (1) Garage List 2010 BMW 335i [0.00]	After a tune I've heard that besides plugs, coils and injectors will degrade a lot sooner than normal so don't discount it just cause you did the plugs. Have you pulled codes? __________________ COBB AP Stg 2+ FMIC Aggressive \| VRSF 3" Catless DP \| COBB FMIC \| BMS DCI \| CP-e Metal Charge Pipe \| 370+ whp/435+ lb.ft torque
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