modded engine behavior
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
modded engine behavior
I have one issue I can't seem to overcome so I thought I'd ask around to see if I am wasting my time. My car runs great, everything with the idle is good as long as it is warmed up. When I start it cold it will fire immediately but will not stay running without help from the throttle. Once it gets a few degrees warmth in it, it will idle by itself but real low, down around 500. The tune is programmed for a 950 idle and as I said, it is perfect as long as it is warm. Is this common with a modded efi engine? If not, what can be done?
Melting Slicks
Joined: Mar 2008
Posts: 2,141
Likes: 76
From: Santa Maria, CA
I have one issue I can't seem to overcome so I thought I'd ask around to see if I am wasting my time. My car runs great, everything with the idle is good as long as it is warmed up. When I start it cold it will fire immediately but will not stay running without help from the throttle. Once it gets a few degrees warmth in it, it will idle by itself but real low, down around 500. The tune is programmed for a 950 idle and as I said, it is perfect as long as it is warm. Is this common with a modded efi engine? If not, what can be done?
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
The fan comes on at 185, off at 175 if I recall. If there is a specific temp programmed in the tune, I am unaware of it. I have noticed that my idle does come up immediately on reaching 125 degrees if this helps.
Burning Brakes
Joined: Mar 2013
Posts: 1,131
Likes: 5
From: Illinois/Wisconsin Line
Doesn't sound like a problem and only operator error
Just buzz it up to 1500 rpm for 1 min then hold it at 2000 to 2200 rpm for another 2 mins. Then it should idle fine. Otherwize start playing and looking at anything with closed loop crap on start up. High o2 cross counts/throttle body r&r and soak and cleanup of small carbon ledge behind throttle blades. IAC/TPS Base Idle
Or just hook up a electric sol to the vac line to fuel reg on a switch for u to throw and bleed off all the vac to richen up mixture. Should help a lot on start up
Just buzz it up to 1500 rpm for 1 min then hold it at 2000 to 2200 rpm for another 2 mins. Then it should idle fine. Otherwize start playing and looking at anything with closed loop crap on start up. High o2 cross counts/throttle body r&r and soak and cleanup of small carbon ledge behind throttle blades. IAC/TPS Base Idle
Or just hook up a electric sol to the vac line to fuel reg on a switch for u to throw and bleed off all the vac to richen up mixture. Should help a lot on start up
Safety Car
Joined: Sep 2001
Posts: 4,134
Likes: 531
From: Glenbeulah Wi
I have one issue I can't seem to overcome so I thought I'd ask around to see if I am wasting my time. My car runs great, everything with the idle is good as long as it is warmed up. When I start it cold it will fire immediately but will not stay running without help from the throttle. Once it gets a few degrees warmth in it, it will idle by itself but real low, down around 500. The tune is programmed for a 950 idle and as I said, it is perfect as long as it is warm. Is this common with a modded efi engine? If not, what can be done?
-Open loop too lean or rich, if you can check with a WB sensor that would help, make tune adjustments
-IAC position out of range due to the throttle blades being closed too far. Scan the car and see where your warm IAC position is at idle in park, should be around 10 counts.
-Cold idle spark adder may be too low
There could be other issues but I would look at these.
Team Owner
Joined: Sep 2001
Posts: 62,067
Likes: 1,723
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
First thing I'd be checking was above, IAC position. Then the lean/rich in open loop condition.
Then I'd think its in the chip settings.
Then I'd think its in the chip settings.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
It may very well be in the IAC position. I cannot for the life of me seem to get that damn thing set right. I'll check it out one more time, I have used the standard method and I have tried to get it set by scanning but I cannot got the counts right no matter what I do and what I am doing is probably wrong. IAC seems to work good though when it is warmed up, keeps the idle right up there when I put it in gear and/or turn on the a/c. My main problem may or may not be in the fact that I am running an LS style throttle body with the corresponding IAC. but I was told they set the same way.
Burning Brakes
Joined: Mar 2013
Posts: 1,131
Likes: 5
From: Illinois/Wisconsin Line
There ya Go. Something u left out but anything really thats not in closed loop, really is not a problem. I'd say play with the numbers not varying to much to screw it up in closed loop or just trick the system with a diverter sol on a switch for the fuel pump reg to get it a little rich when cold by tricking the system into full fuel output pressure by thinking its at full throttle/wot or maybe a real small hole in the throttle body butterfly to get the throttle more closer to its closed position and lowering o2 cross counts and also at the same time allowing more air to pass through and richening it up to where it needs to be with ur set up
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