Whats the cure for this?
Whats the cure for this?
one thing you run into with TBI is that the fuel pools on the plates then dribbles into the throttle body. this means any adjustments your ECM makes to fuel or IAC or whatever can be really delayed so it's really fighting with itself
to minimize this, the first thing to try is to make sure most of the fuel is actually spraying through the throttle plates rather than puddling up on them. this usually means you start cracking the idle stop screw until your IAC counts get very low (but not zero ideally) at HOT idle.
most people find that the lower the iac count the better the idle on TBI engines.
other than that give it a bit more (or less?) timing and a bit more fuel
a lean condition or incorrect timing advance can give you a really unstable idle, and the ECM will just make it worse trying to correct for it.
THANKS !! I did open the throttle plates some but I was not sure how much I can go with out disturbing something else in the process..I will take if further and see what happens…
Anyone try to drill a small hole in the plates? We did this in carbs with big cams to still have a handle on the T-slot opening and let enough air in to get the idle constant…
i'd try to open the plates until your hot IAC counts are around 10 or so
i know that some ecms get complainy when you move the throttle plates around (as it thinks you have your foot on the gas) so sometimes TPS readjustment/relearn or power cycling the ECM would be necessary before it'll go back into 'idle mode'
This .pdf may help, it shows how to set your min idle and then calibrate your TPS.
Explain how the IAC works.. I know it opens to allow idle but does it completely close with the throttle open wile driving? Will there be an issue with it with the counts that low? Dumb question I guess as I’m sure you have done it and it works..
Gotta give that I try..So if the TPS is above ? At idle where is it acceptable and think is should be at.50 volts…
Thanks
When the engine is cold, the IAC opens to maintain RPMs until it warms up. Attached is an explanation from TunerPro RT on IAC vs CTS.Originally Posted by C2500
Once warm, as @Steveo suggested, you can play with the throttle blade to get IAC counts down to ~10. Looking at a couple logs mine runs ~15 at 650 RPM. When you accelerate the IAC opens up, sometimes over 150 counts. Then, if you let off the pedal and slow down, the IAC will close slowly until you reach targeted idle speed.
On my TPS, it's ~.45V which shows -1%. If the ECM/PCM sees a certain voltage above the threshold set in the calibration, it thinks you're no longer idling and have the pedal depressed so, AFAIK it doesn't look to control your idle.
Edit: the ECM may also cut off fuel when cranking thinking you're in a flooded condition.
Last edited by PlayingWithTBI; 07-10-2021 at 06:38 PM.
How do you have your stall saver set ? This can make it surge.
Stall saver??? I have set the IAC counts to 10ish hot in park and I adjusted the tps at .50volts. It’s better but still have its moments of surging sitting at a traffic light.. I did notice that the cruse in high (OD) with the RPM at about 1600 that surge is gone..
I cleared the ECM and going to give it a good drive to see if that helps as It did in the past..
It’s got a stroker 383 in it with a hyd roller cam and a 454 TBI unit on it…
play in throttle shaft?
In Tuner Pro, XDF, 0D_TPV5_V250. "Stall Saver Activation Threshholds" These are Scalars you can mess with. These definetely caused mine to surge. my ADX is A217_0D_V250
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