If the engine spins up too high RPM after cranking and takes too much time for iac-dc (check your logs in spreadsheet or logviewer!!!) to start to decrease, your iac_integral_inc_limit is too high.
If that does not lower the idling speed, then check that the 'TPS value for idle threshold (%)' -> (menu Extras -> Idle Settings General -> Idle Settings page in Megatune) has higher value than the actual Throttle Position value when throttle is closed.
If the engine has tendency to stall, than maybe the iac_integral_dec_limit is too high. But remember there can be MANY other reasons for this to happen.
The MembersPage/MarcellGal/EngineSwap is a weak 1.6L engine. It often stalled with air-conditioner. The solution was to make the control authority as narrow as possible, with smallest iac_integral_dec_limit and iac_integral_inc_limit values.
Tuning warm engine first (the iac coolant dependent reference positions for lower coolant temp can only be tuned afterwards). This car has stepper iac, but same applies for PWM iac. Eg. the engine needed
- iac position=29 when AC and lights were off (without load)
- iac position=41 when AC and lights were on (max load)
- the AC is much more significant load, the lights is only 1 iac position or less
I set the iac reference position (at max coolant temp) to decimal 38.
- I decreased iac_integral_dec_limit until the engine cannot regulate without load, that is iac position=30 resulted in slightly raised idle (iac_integral_dec_limit was appr 24 decimal in my case, but this also depends on integral value)
- I decreased iac_integral_inc_limit until the engine cannot regulate at max load, => iac_position=40 cannot maintain the idle target (iac_integral_inc_limit was appr 6 decimal, but this also depends on integral value)
Obviously, I increased the limits slightly (from 24,6 in the example to 25,7 or maybe add some more margin and 27,8).
- narrow iac authority-range
- and setting the reference position a bit higher than the middle, as 38 is higher than (29+41)/2
I have suggestion for little change regarding IAC follows tps when not idle. Now IAC position jumps to reference table value when not idle. It cause some transitional jerk if real IAC position is some % or steps less than reference.
There can be two solutions:
- follow from current position
- stay at current position
Choosing to disable did not help much.
In addition if turbo used and intake end of valve is not connected post turbo, there is no way to close 2-wire BOSCH PWM valve. It opens in "limp home" mode and cause boost leak.
- move to definite position. Slow if little throttle, fast if more.
Just try 1.1.41 on real car: Jaguar with 4.2 6cyl inline. Target is smooth drivebility and nothing else. My basic reason to try new code was iacref_matslope - feature what allows rise up PWM valve reference position in traffic jams, where IAT goes rocket high. I try two extremely different circumstances: simulate traffic jam (IAT around 60degC) and idle after extended highway driving(IAT 20degC). Looks like maximal 3%PWM slope @70degC still not enough. I think maximal must be around 10%DC - it must be more than enough. I use BOSCH valve from OPEL. Idle 700Rpm.
Also baffle for smooth driving is my previously described issue with IAC follows tps when not idle from ref position whitch is allways little higher tahn real idle DC.
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