RPM dips at idle
#1
RPM dips at idle
Occasionally my car's idle will dip to about 600 RPMs at idle (like when I pull up to a red light and stick it in neutral) and slowly creep back up to normal RPM. Never stalls, etc.
I also notice that the Air/Fuel spikes to around 16.5+.
Car is tuned by STM with Walbro 255, STM full intake and intercooler hoses and MBC, so pretty much stock.
Is this normal? Why would there be so much air in the fuel?
I also notice that the Air/Fuel spikes to around 16.5+.
Car is tuned by STM with Walbro 255, STM full intake and intercooler hoses and MBC, so pretty much stock.
Is this normal? Why would there be so much air in the fuel?
#4
EvoM Community Team Leader
iTrader: (60)
anyway, could be a lot of things.
fuel pump
injectors
relay
wiring to fuel pump or injectors
alternator
BISS out of adjustment
IACV
error in the tune
and more.
start with the simple/free stuff and go from there. good luck, dude!
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#5
It's great, isn't it? ![lol](https://www.evolutionm.net/forums/images/smilies/lol.gif)
Thanks, I will start with plugs and go from there. If plugs are fine I will continue driving it, and if it gets worse I will take it to STM and have them diagnose. Like I said, never stalls out or anything major like that, but I have noticed that it is happening more often.
![lol](https://www.evolutionm.net/forums/images/smilies/lol.gif)
Thanks, I will start with plugs and go from there. If plugs are fine I will continue driving it, and if it gets worse I will take it to STM and have them diagnose. Like I said, never stalls out or anything major like that, but I have noticed that it is happening more often.
#11
EvoM Guru
iTrader: (1)
Yea. Sound alike the BISS is adjusted wrong. When is the "test mode" to set the BISS, the engine should idle roughly 100rpm higher than your target idle.
#12
EvoM Community Team Leader
iTrader: (60)
i haven't decided which method i like best, but adjusting the trim seems to work a bit better for me.
#13
I'll have to schedule a time to get STM to look at the BISS screw. I am new to the Evo community and have never even heard of BISS before, so I think I'll leave that adjustment to the professionals.
What is the worst case scenario if I don't take the car in right away?
What is the worst case scenario if I don't take the car in right away?
#14
EvoM Guru
iTrader: (1)
Worst case, it just continues to do what it's doing. You're not going to hurt it.
The BISS is the Base Idle Screw Setting or something. It sets the idle speed to a "base" setting, then the IACV makes fine adjustments to maintain idle. If you search around there are threads explaining how to adjust.
The BISS is the Base Idle Screw Setting or something. It sets the idle speed to a "base" setting, then the IACV makes fine adjustments to maintain idle. If you search around there are threads explaining how to adjust.