fluctuating idle speed from 600-900 RPM- normal ??
10-30-2003, 02:04 AM
#1
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fluctuating idle speed from 600-900 RPM- normal ??
Thanks to everyone who has helped me get acquainted with my new 92 C4. I have another question about my idle speed that's been bugging me!
It seems that regardless of engine temp, the engine will cycle through an idle speed of about 700-900 RPM, especially when cold. When it is warmed up, the idle speed on the tach slightly moves but I can tell it's fluctuating by the noise and also the oil pressure gauge that goes up and down by almost 1 bar. Seems fine, but I am just curious if everyone else's idle bounces around a bit. My 65 911 has a solid idle even though it's almost 40 years old! Just wanted to be sure my C4 is healthy!
It seems that regardless of engine temp, the engine will cycle through an idle speed of about 700-900 RPM, especially when cold. When it is warmed up, the idle speed on the tach slightly moves but I can tell it's fluctuating by the noise and also the oil pressure gauge that goes up and down by almost 1 bar. Seems fine, but I am just curious if everyone else's idle bounces around a bit. My 65 911 has a solid idle even though it's almost 40 years old! Just wanted to be sure my C4 is healthy!
10-30-2003, 04:06 AM
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Dear Garrett,
First thing to do is to disconnect the battery. Leave disconnected for at least 20 mins if you have airbags. Then reconnect battery. Start engine (keep your foot away from the accelerator pedal). Allow to idle for at least 2 mins and then without shutting down go for a drive using as many rpms in as many gears as you can. This is called a DME reset and this procedure allows the DME to learn how you drive the 964.
If this does not work the next thing you check is the oil contamination of the airflow sensor assembly. Overfilled of the oil which is very common with 964 owners results in oil being vented into the airflow sensor assembly and the idle speed control valve. The ISV may well need a clean out. You initially check for oil contamination by removing the airfilter and checking inside the airbox for oil residue.
There are many other causes but these two are the most common. I also recommend you check the voltage across the battery with the engine off, engine at idle and then at 2000 rpm and report your findings.
Ciao,
Adrian
964C4
First thing to do is to disconnect the battery. Leave disconnected for at least 20 mins if you have airbags. Then reconnect battery. Start engine (keep your foot away from the accelerator pedal). Allow to idle for at least 2 mins and then without shutting down go for a drive using as many rpms in as many gears as you can. This is called a DME reset and this procedure allows the DME to learn how you drive the 964.
If this does not work the next thing you check is the oil contamination of the airflow sensor assembly. Overfilled of the oil which is very common with 964 owners results in oil being vented into the airflow sensor assembly and the idle speed control valve. The ISV may well need a clean out. You initially check for oil contamination by removing the airfilter and checking inside the airbox for oil residue.
There are many other causes but these two are the most common. I also recommend you check the voltage across the battery with the engine off, engine at idle and then at 2000 rpm and report your findings.
Ciao,
Adrian
964C4
10-30-2003, 12:43 PM
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Adrian, thank you for your tips. I will look at the air cleaner box tonight since I am curious to see if it was ever overfilled. And I will also do the DME reset since I want my car to know "me" instead of the previous guy!!
Thanks for your input and time, I really appreciate it.
Thanks for your input and time, I really appreciate it.
10-30-2003, 01:05 PM
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[QUOTE]Originally posted by Adrian
Leave disconnected for at least 20 mins if you have airbags.
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I've printed this off, just in case I need to do the DME reset in the next month before I get my book. Just a quick one though Adrian, do you only have to wait 20 minutes if you have airbags? To do this reset on a non airbag car like mine can you re-connect the battery straight away?
Cheers
Leave disconnected for at least 20 mins if you have airbags.
-----------------------------------------------------
I've printed this off, just in case I need to do the DME reset in the next month before I get my book. Just a quick one though Adrian, do you only have to wait 20 minutes if you have airbags? To do this reset on a non airbag car like mine can you re-connect the battery straight away?
Cheers
10-30-2003, 01:35 PM
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Dear Dave,
This only actually applies to airbag equipped 964s. However I like to allow all to stand for 20 mins though because it ensures ALL capacitive circuits have been discharged. These circuits are found in the DME and in the aircon and heating control unit. Leave at least 5 mins for non airbag equipped you must ensure the adaptive memory is completely lost,
Ciao,
Adrian
964C4
This only actually applies to airbag equipped 964s. However I like to allow all to stand for 20 mins though because it ensures ALL capacitive circuits have been discharged. These circuits are found in the DME and in the aircon and heating control unit. Leave at least 5 mins for non airbag equipped you must ensure the adaptive memory is completely lost,
Ciao,
Adrian
964C4
