XFI cold start low idle problem
- Thread starter CS99
- Start date
NY Twin Turbo
All the good stuff.....Times 2.
- Joined
- Dec 10, 2014
If it's showing a high IAC position in the throttle follower, and it's not maintaining a higher warm-up idle as commanded in your "idle speed vs coolant temperature" graph, then maybe your IAC isn't working. Or at least not during cold conditions.
Don't jump to conclusions just yet that the IAC is bad though. Look around a little more. If all else fails......Change the IAC.
Don't jump to conclusions just yet that the IAC is bad though. Look around a little more. If all else fails......Change the IAC.
You cut on Key and wait a few seconds before cranking?
I think the XFI will cycle the IAC motor open or closed at least once to make sure it has correct starting point. To find home position.
You have the XFI dash display thingy? I love that!
I can see when I have started car maybe too fast and I have strange IAC position values that are not normal for me.
I just power down the XFI.....turn key on and wait 4-5 seconds and then start again.
Or, could be One or more of a whole list of things? lol
I think the XFI will cycle the IAC motor open or closed at least once to make sure it has correct starting point. To find home position.
You have the XFI dash display thingy? I love that!
I can see when I have started car maybe too fast and I have strange IAC position values that are not normal for me.
I just power down the XFI.....turn key on and wait 4-5 seconds and then start again.
Or, could be One or more of a whole list of things? lol
Its weird, I think I may have to much cranking fuel when cold, the autolite 103 plugs are fouled. Switching to 104. I have GN1 aluminum heads. I think motor is loading up on fuel and not giving me a high idle. Afr is dropping to low 10's and even high,9's right after the engine fires.
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Sent from my VS986 using Tapatalk
OK. I logged startup. IAC is opening to 135. but car doesnt high rev when starting. I can control the idle in the throttle follower table, so I know the IAC is working. The iac works flawless other than at startup. on Idle parametersI have 33 for the P Gain and 5 for the D Gain.
I just started the car with coolant temp at 150 deg. It started and did not rev up when it first fired, I shut car off and when I restarted it, The Idle went high then slowly came down to 950 rpm like it supposed to. This always happens after the car has been sitting. I can go restart it again 50 times and everything is ok. I did replace the IAC and that didnt make any difference
Im not getting the engine to rev up at initial startup. My AFR is 14.0. I think that is my problem. When cold the engine should idle at 12.5 afr. My IAC is all the way open when cold but engine idle wont increase because its to lean. I will try an give it more fuel vs coolant temp.
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You mean rev-up when you play with accelerator pedal? Or, just the ECU trying to rev using IAC?
Your FAST shows that it thinks it is all the way open, but is it really?
That is what I was trying to tell you I think is happening sometimes with starting too quickly using FAST.
The process of homing the closed position may not have completed by the time you start to crack.
So...the IAC values of position are wrong. (Just an idea, because I have seen same thing on my car)
Turn ON ignition but no crank yet.....count to 5....then crank it up
Your FAST shows that it thinks it is all the way open, but is it really?
That is what I was trying to tell you I think is happening sometimes with starting too quickly using FAST.
The process of homing the closed position may not have completed by the time you start to crack.
So...the IAC values of position are wrong. (Just an idea, because I have seen same thing on my car)
Turn ON ignition but no crank yet.....count to 5....then crank it up
The ecu says iac all the way open but idle not increasing. My afr is 14 when starting. I am going to add fuel in the coolant temp table. I think car just cannot idle faster add startup because it to lean. i think I need AFR of 12.5 when cold
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Sent from my VS986 using Tapatalk
The O2 sensor is not 100% correct right at start-up man.
It need a little time to heat up, and to burn off humidity that forms to read accurately.
I think my car ignores the o2 sensor for a certain duration after start-up....then it begins to use it in closed-loop after a while. I bet yours does too.
Ignore the O2 for the first 10-30 seconds of running, maybe even longer?
Yes, I understand you....but I think you are not understanding me.
The ECU only thinks the IAC is fully open. But it may not physically be fully open due to starting too fast.
How is this possible you may ask??
Because the FAST cycles the IAC motor to find a good known position....a "home position" to start counting from.
If you start car too fast, then you mess up this process and the value you are looking at on your PC may not actually be correct. Got it?
I fix CNC machines and 3d printers and work a lot with motion-control system and motors and 5hit like that for a living.
Of course, if your VE tables are way off around idle or other parameters/tables then you need to address that first
It need a little time to heat up, and to burn off humidity that forms to read accurately.
I think my car ignores the o2 sensor for a certain duration after start-up....then it begins to use it in closed-loop after a while. I bet yours does too.
Ignore the O2 for the first 10-30 seconds of running, maybe even longer?
Yes, I understand you....but I think you are not understanding me.
The ECU only thinks the IAC is fully open. But it may not physically be fully open due to starting too fast.
How is this possible you may ask??
Because the FAST cycles the IAC motor to find a good known position....a "home position" to start counting from.
If you start car too fast, then you mess up this process and the value you are looking at on your PC may not actually be correct. Got it?
I fix CNC machines and 3d printers and work a lot with motion-control system and motors and 5hit like that for a living.
Of course, if your VE tables are way off around idle or other parameters/tables then you need to address that first
Ok, i see. I have always turn the key on for a few seconds to let the fuel pump prime before I start it. You are correct about the O2 sensor delay. I will check and see if and where I can change that. I know I got closed loop set to 90 degrees.
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Crack your throttle blade a little more open with the set screw if you constantly have iac numbers above 120. The 70 position is meaningless.
Probably just what you have start upbiac position set to in the fast software
You can set the start up iac position to anything within its range....but you want it to start of course! Lol
If you find a good number then it should start without playing with the pedal.
Maybe extreme cold or heat requires a little tweeking of something
If you find a good number then it should start without playing with the pedal.
Maybe extreme cold or heat requires a little tweeking of something
