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OK I am messing with my friends t/a and its an auto, never really did much with them. When you put the thing in reverse to back up and give it some gas then let off and hit the brake the rpms dip down a good bit, I am going to mess with it some but I just watned to see what you guys had to say, its stock pretty much except for a lid, vig 3200 and a shift kit.
from the looks of it the IAC motor is closing abruptly and its only in reverse, p/n its ok as well as in drive, but reverse it wants to act up.
Sounds like a Q: for Chris.
EC
the PCM only knows p/n and in gear. shifting from P/N to D or P/N to R the IAC behaves the same way.
Chris...
What is your throttle cracker enable/disable speed set at?
Just bump the gear airflow up a bit, worked just fine on my 4l60e.
Chris
this is happening at like 1 mph max maybe. it is in neutral if you give it a quick tap of the gas then the brakes or jsut a quick tap of the gas just as the car barely starts to move.
i dont want to bump up the idle air becuase its already pretty damn high, but i will check it out. the issue is only reverse as well, doesnt do it if it is in drive
oh ok, see mine did it in both. So scratch my idea.
Chris
See what your spark advance is doing compared to the g/cyl air going from P/N to D and then P/N to Reverse.
Spark may drop more as there is more line pressure in reverse than in forward gears at idle.
That function is called Garage Shift. It's been in the 4L60E since the beginning. Not a table that we have access to though. (Not usually needed either except in extreme cases)
EC
ok thanks, the tune is otherwise stcok except for gear changes and shift points