It is there because with all load on the engine, lights, heater, and wipers, TPS can reach 6% at idle, normal idle TPS 4 to 5%
On cold start and warm up TPS is about 8% If i set idle threshold to 8% there is no leeway and idle control is not in effect, resulting in a frozen stepper above the threshold, this is with follow TPS enabled. If you dissable follow TPS, on starting the engine the stepper freezes above threshold and engine sits at around 2500rpm.
No matter where the threshold is (As long as its higher than idle TPS)TPS always drops to well below idle TPS when on over run out of over run fuel cut, not above.
If I were to set Idle threshold to 2 or 3 % as you suggest, I would have no idle control and the stepper would freeze, considering that idle TPS is on average 4%. Its confusing, the PID refference table has an effect
Normal cruse TPS is around 12 to 14% TPS
Think about an over run situation without worrying about whatthe idle threshold is set to for a minuit. You lift off the throttle, throttle closes, TPS is below idle threshold, so idle control resumes, yet engine speed is above idle set point. Idle control reduces steps, thus TPS, to try and bring engine speed down to idle set point. Problem is the engine is in over run, not idle. Throttle is totaly closed, deep vacuum is registered, 5kpa ( bad for the 50 year old designe A series oil consumption), engine speed aproaches idle set point, overshoots, yet stepper does not respond quick enough, not enough air in the engine and the engine stalls.
Stepper and idle control works well, espetialy with a high ignition advance in the very low rpm load sites. You can keep your foot on the brake, bring the clutch in and watch the stepper open up the throttle, advance increase, and feel the torque of the engine build up, I could not stall the engine easily this way.
If I recall correctly how rover prevented this situation. As the throttle is released on over run, the stepper would catch the throttle and return to a predetermined set point of roughly 35 steps as the engine speed aproaches idle set point, then if required at this point would adjust from there. With this OEM system you tune the throttle stop to achieve idle speed at this 35 steps, so in theory the stepper should return to idle set point every time. This is one reaon i set the minimum PID refference bin to 40 steps, but unable to see what steps is current, its not easy.
I have tried all sorts of figures in the last bin of the PID stepper reference table, which i would have thought would have been the idle steps set point, yet this situation still exists. I have looked around but cannot find anywhere that reports back the number of steps, again making it difficult to see what is realy going on. A Megatune Gauge would be nice, showing the max number of configured steps on the scale and the current stepper position in relation, % would confuse things. What also would be nice is a warning light at the bottom of Megatune to show when idle control is actualy on, much like the one for EGO and Stepper. though you could assume that if stepper is on that you are in idle control? While Im at it ( again) whats wrong with having a status light for the misc outputs to show its current state, whether its on or off, cant be that demanding on software
There needs to be a configurable point in idle control for steps at idle set point and an idle enrty speed thus preventing the stepper clossing off the throttle at high over run engine speeds
Rover originaly used a switch on the throttle pedal to determine idle condition. The problem was the switch would fail. I recently fixed one of these after A very well known and renowned Mini specialist couldnt fix the problem, the car would backfire, hesitate and run badly, so much so it melted the cat. The cat was replaced for it to melt again within two days!! a complete injection manifold was fitted which included all sensors, the problem still existed. I looked at it and found the problem within 10 minuits, now im not being big headed, but it really does show the skill level of these so called experts. when you moved the throttle the stepper moved to zero and the advance retarded to the point of inlet backfire, incomplete combustion in the exhaust melting the two cats. The owner had spent over £500 at the garage for what, in the end was only a £20 switch. I ripped out the old ECU and installed and rewired for a later version that did away with the switch, and it cost him no more than a pint afterwards. Point im getting at, i can see this as very similar to the problem im having, though i havent managed to get it to go pop yet, lol. Well i can when restarting it, ooh, now i wonder.
Sorry i do tend to ramble on a bit
