RPM dip on startup?

BAK613 · 10-30-2010, 05:15 PM

Quote:

Originally Posted by RickC

One thing worth a try (works for me) is to turn the key to the point just prior to the engine cranking but allowing the fuel pump to start and prime for about 5-10 seconds then turn to start. Having the fuel pump started and primed gets rid of most of the dip for me

I haven't driven the car since last week. So this afternoon I followed your recommendation. Turned the key to on, did a slow "five count". and the engine started with out any dip. Went up to about 1200 and then settled nicely at about 1000 RPM.

Bruce

Diesel_d66 · 03-25-2018, 09:10 PM

I just got a 07 MR and this morning after a few days of sitting the car started and the revs dropped and stalled. After restarting the revs dipped and rebounded to around 1200.

Also is normal idle at operating temp around 1k?

StickMon · 03-25-2018, 11:18 PM

Yes and mostly yes.
Worse when it's chilly.
You learn to give it a tiny bit of gas 1 second after starting to help it thought the dip.
(Thanks to Salty for this tip. I always cover the gas pedal now after starting in case it needs a little help.)
Nominal idle when everything is up to temp is 870.
I get anything from 850 to 950, but most often 870-900.

Diesel_d66 · 03-26-2018, 01:14 PM

Thanks Stick, I'm actually more concerned about normal temp idle. Mine seems to be around 1k. Anyone else around the 1k point? or are most M zeds around 800-900?

elerner61 · 03-27-2018, 09:56 AM

My idle definitely settles below 1K once warming/warmed up.

Diesel_d66 · 03-28-2018, 03:57 PM

Quote:

Originally Posted by elerner61

My idle definitely settles below 1K once warming/warmed up.

I took it for a spin and wash last night and give the idle a closer look and looks like mine is also below the 1k line.

Clearancediver · 03-30-2018, 11:25 AM

Has anyone considered that the start up dip issue indicates a fuel filter needing to be changed. Possible explanation for having to wait for fuel pump to pressurize the fuel system... once I changed mine the pressurization cycle was near instantaneous compared to prior filter change pressurization cycle.

Dirty filter causes a number of issues with startup in a car...

Given that the filter is internal to fuel tank it's not something that gets changed in routine maintenance. The saddle fuel tank containing the fuel pump/filter needs to be drained to do the change...

schwank · 03-30-2018, 12:27 PM

Mine has done this since 2006

ried · 03-30-2018, 12:34 PM

This happened on my previous M Coupe. I'm not saying this is the cause, but it coincided with the dealer accidentally leaving the crankcase breather valve disconnected from the valve cover after a service appointment. This resulted in a little oil splashing up onto the hood, of course, but the most noticeable side effect was the RPM dip upon cold start. I reconnected the crankcase breather valve, cleaned up the oil, and didn't have the issue again.

Correlation does not equal causation, of course, and your mileage may vary.

03-25-2018, 09:10 PM	#46
Diesel_d66 Private 8 Rep 71 Posts Drives: '07 MR Join Date: Oct 2013 Location: Baltimore iTrader: (0)	I just got a 07 MR and this morning after a few days of sitting the car started and the revs dropped and stalled. After restarting the revs dipped and rebounded to around 1200. Also is normal idle at operating temp around 1k?
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03-25-2018, 11:18 PM	#47
StickMon My other car is on Mars 636 Rep 3,124 Posts Drives: 2006 MR Join Date: Feb 2011 Location: Lo-Cal iTrader: (1)	Yes and mostly yes. Worse when it's chilly. You learn to give it a tiny bit of gas 1 second after starting to help it thought the dip. (Thanks to Salty for this tip. I always cover the gas pedal now after starting in case it needs a little help.) Nominal idle when everything is up to temp is 870. I get anything from 850 to 950, but most often 870-900. __________________ Warning: May contain traces of nuts.
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03-26-2018, 01:14 PM	#48
Diesel_d66 Private 8 Rep 71 Posts Drives: '07 MR Join Date: Oct 2013 Location: Baltimore iTrader: (0)	Thanks Stick, I'm actually more concerned about normal temp idle. Mine seems to be around 1k. Anyone else around the 1k point? or are most M zeds around 800-900?
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03-27-2018, 09:56 AM	#49
elerner61 Major 157 Rep 1,107 Posts Drives: '07 Z4M Roadster Join Date: May 2011 Location: Mount Kisco, NY iTrader: (0)	My idle definitely settles below 1K once warming/warmed up.
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03-30-2018, 11:25 AM	#51
Clearancediver Lieutenant 90 Rep 406 Posts Drives: 2004 Z4 Join Date: Oct 2012 Location: Victoria, BC Canada iTrader: (0)	Has anyone considered that the start up dip issue indicates a fuel filter needing to be changed. Possible explanation for having to wait for fuel pump to pressurize the fuel system... once I changed mine the pressurization cycle was near instantaneous compared to prior filter change pressurization cycle. Dirty filter causes a number of issues with startup in a car... Given that the filter is internal to fuel tank it's not something that gets changed in routine maintenance. The saddle fuel tank containing the fuel pump/filter needs to be drained to do the change... __________________ Sent from my smart phone...
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03-30-2018, 12:27 PM	#52
schwank First Lieutenant 30 Rep 317 Posts Drives: 06 z4 m coupe Join Date: Nov 2006 Location: cincinnati iTrader: (0)	Mine has done this since 2006 __________________ K&W v3, APR splitter, magnaflow axle back35% tint, stubby antenna, Jet black, and interlagos blue stock wheels, clutch delay delete, illuminated ZHP shift knob, Leather Z m shift boot, and arm rest.
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03-30-2018, 12:34 PM	#53
ried Captain 792 Rep 817 Posts Drives: F31, F80 Join Date: Feb 2013 Location: SoCal iTrader: (2)	This happened on my previous M Coupe. I'm not saying this is the cause, but it coincided with the dealer accidentally leaving the crankcase breather valve disconnected from the valve cover after a service appointment. This resulted in a little oil splashing up onto the hood, of course, but the most noticeable side effect was the RPM dip upon cold start. I reconnected the crankcase breather valve, cleaned up the oil, and didn't have the issue again. Correlation does not equal causation, of course, and your mileage may vary.
	Appreciate 0 Quote