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I'm tuning a 3sgte mr2 turbo motor freshly rebuilt with 268 duration cams and a larger intake manifold(TVIS DELETED) and throttle body with and adapter plate that utilizes the factory iacv and factory TPS.
With the old engine(factory cams and factory intake manifold with TVIS)the car was already tuned and running well with the map that the previous tuner had made for it. Upon startup with this new motor, idle was erratic and close to stalling. I turned off closed loop idle and leaned the afr in the idle areas between 800 and 1300, but the issue is I cant seem to get the car to idle below 1200. As if the iacv won't close up enough to restrict airflow?
I haven't check for vacuum leaks yet, but I will. Shouldn't be any tho, as I was meticulous about the vacuum hose routing and connections.
As a general rule of thumb, when going from small cams larger cams, does the idle mixture get leaner or richer? Also, with ignition timing, do we typically advance or retard.
I turned off the closed loop wideband stoichiometric setting also to help prevent any swings or surges while I tried to dial in fuel table in idle area.
Any advice is appreciated. Thank you.
I'm realizing now hat haven't yet messed with the base position table. Would that need to be adjusted with different cams?
What is the main function of idle base position table vs idle target table? I think I assumed that all I needed to adjust was target table and afr, but after reading through forum I'm seeing I should be adjusting base position table?
As a quick test to confirm if it is idle valve settings or an air leak somewhere else you could just unplug the idle valve (or turn off the aux output). If the idle instantly drops then that would indicate you have a setting problem. If it doesnt drop then you have an air leak or the throttle blade is set open too far.
For tuning the base position table you switch the idle speed control to open loop mode and adjust that table until you have a roughly correct idle speed at all operating temperatures. Like most functions in the Link ECU, the idle speed control tuning procedure is fairly well documented in the help file.
Open loop setup:
Once you have open loop control setup and working reasonably well, then if you wish you can switch over to closed loop mode and tune that as per the closed loop setup guide below:
Just want to say I was able to get a very stable idle by adding more air to the base idle position and retarding the ignition timing to get the idle lower. Went from approximately 20 degrees of timing down to 13. It has a stable idle around 1050 which I think is a good idle considering the aggressiveness of the cams. Initially I was trying to advance the ignition close to 30 degrees with less base position idle air and it made the idle very unstable and inconsistent probably because motor was choking for air. Thanks for the help. Learning more every day.
How much .050" overlap on the cams? A 268 is not generally aggressive, particularly if it's a dedicated turbo grind
Generally speaking a little more ignition advance and fuel helps with hot cams but 30 degrees at idle is too much .
I am tuning a 3sgte with 264 cams and idle very well behind 900-1000 rpm with 15-18 degrees atdc and a/f ratio around 12.5
with the idle valve deleted.