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Lightning will accelerate on its own

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#21 ·
Leaky fuel injector ? They could get Debra’s that stick them open perhaps 🤷🏻‍♂️
 
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#23 ·
Most likely the truck is ingesting too much air to meet commanded. The throttle blade may very well need to be set lower regardless of what TPS says. The truck when first keyed on always "Ratches" and uses the lowest TP value to determine TP relative from there on. As far as the IAC if it is at 31% at hot idle in park that too me says the throttle blade is not open enough as I always shoot for mid to low 20%... 21% usually is the lowest value possible and means the IAC is doing absolutely nothing. Again, throttle blade needs to be set in park with the truck hot... Ideally at operating temp for several minutes. Now if in gear the truck wants to take off under it's own power, your ISC multiplier tables most likely need to be scaled back at that temp range. You need to see how much error there is in the IAC... I don't use SCT anymore but I believe they call it idle air integrator. This is essentially like a fuel trim for the IAC as it is in closed loop just like the O2 sensors. If you disconnect the IAC and all the problems still exist then you have a vacuum leak, a suspect throttle blade, or a bad IAC.
 
#24 ·
Dusten said:
You shouldnt adjust the throttle screw and your tps is already right based on your data log.
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Not necessarily... If it were my truck I would get it absolutely hot idling in park and back off the throttle blade. If he can get it down to where the truck is reaching commanded idle then the throttle blade was most likely the issue. If he can't then the truck is ingesting air elsewhere..
 
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Discussion starter · #25 ·
slow94 said:
Not necessarily... If it were my truck I would get it absolutely hot idling in park and back off the throttle blade. If he can get it down to where the truck is reaching commanded idle then the throttle blade was most likely the issue. If he can't then the truck is ingesting air elsewhere..
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Appreciate all the feed back. I've been triple checking any where I could possibly be getting air in after the MAF. If all else fails I will end up messing with the TB / set screw. Again I appreciate all the feedback as Im not ruling out any suggestions at this point.
 
Discussion starter · #26 ·
Just for refrence. When hot if I disconnect the IAC should I see a significant drop in rpms (almost stalling) or should it drop maybe a couple hundred rpm? Would like to officially cross this off the list.
 
#27 ·
04letsgo said:
Just for refrence. When hot if I disconnect the IAC should I see a significant drop in rpms (almost stalling) or should it drop maybe a couple hundred rpm? Would like to officially cross this off the list.
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It should only drop if the IAC is being used currently to control idle speed. The trucks that I tune, I shoot for no IAC being used at hot idle in park and only let timing control idle speed. That gives me the most range possible for the IAC for when it's cold or have large load swings. However if your truck is idling hot in park and you unplug your IAC and it doesn't fall some then you have too much air entering the engine via the throttle blade or somewhere else entirely. The smallest leak can cause quite a noticeable jump sometimes. Also, sometimes a bad IAC or a cheap replacement IAC can cause issues as well. I have seen them get partially stuck in positions or not be "linear" in airflow compared to their duty cycle.
 
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Discussion starter · #28 ·
slow94 said:
It should only drop if the IAC is being used currently to control idle speed. The trucks that I tune, I shoot for no IAC being used at hot idle in park and only let timing control idle speed. That gives me the most range possible for the IAC for when it's cold or have large load swings. However if your truck is idling hot in park and you unplug your IAC and it doesn't fall some then you have too much air entering the engine via the throttle blade or somewhere else entirely. The smallest leak can cause quite a noticeable jump sometimes. Also, sometimes a bad IAC or a cheap replacement IAC can cause issues as well. I have seen them get partially stuck in positions or not be "linear" in airflow compared to their duty cycle.
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I had a cheap jobber IAC that I replaced with a Hitachi brand IAC because of a hang in the return to idle. It did seem to correct that but now I am having this issue. I did notice 2 spots on my JLT air intake tube (between MAF / TB ) where the grommets might be sucking air in. Sealed them better last night and will put it back on and try it again.
 
Discussion starter · #29 ·
Well not sure I'm making any progress. Haven't touched the TB set screw at all but just made sure I had stuff sealed.
900-920rpm is what it will come down to while the commanded is 750rpm on the SCT engine warm.
Shut engine off, unhook IAC, start it and it would idle around 900-940rpm
I keep hearing a whistle on the driver side once it warmed up. I backed it out of the garage to get a better listen. Once I get to the driver side front wheel / lean in and listen around the wheel well it definitely sounds like it is coming from there.
Took driver wheel off and while listening it seems to be coming from around the front of the engine area near/around the coolant tank / air filter. I think. Started losing my mind trying to pin point it with stethoscope.

Possible intake manifold leak???

I can't seem to get the engine to react to any sort of spray searching for vac leaks.
 
Discussion starter · #32 ·
I may have made some progress.
Warmed truck up.
Unplugged IAC
Adjusted TB set screw (closed a bit) so it was idling just below desired RPM on SCT handheld
Plugged IAC back in, RPMs shot up briefly and came back down and was idling nicely around the desired RPM.
IAC valve % was .28
Shut truck off and reset TPS 199.89 absolute.
Started truck and it came back to desired idle right away.
The whistle has definitely calmed down.
AFR is reading nicely and Short term fuel is still .99% give or take.

Will try to get out for a drive this evening and see if this has solved my problems or not.
 
Discussion starter · #33 ·
Follow up - waited until this morning to go for a drive as I wanted to see if there was any issues with a cold start.
Fired right up, figured itself out quickly and away I went.
Drove around for about 2 hrs and I can confidently say its fixed. Idles perfect, shifts a little nicer and even throttle response has gotten better.

I very much appreciate the suggestions and advice from this group. Going to hop in and go run some more errands today.

Thanks guys!!!!!
 
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04letsgo
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