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1993 Miata with early version of PNP2. 2005 VVT normally aspirated engine and VVTuner. Also has a Innovate MTX-L air fuel gauge. Track only trailered car.
Car has been together like this for 2 years. PNP2 in car for 4 years with another previous engine.
Recently had a dyno tune to address idle and driveability issues. Shop changed from previous open loop to closed loop. I drove one session on track, loaded onto trailer. Got home and with cold engine started right up and idled good and put the car on jack stands for suspension work.
Did not mess with any wiring of MS or any wiring anywhere, just suspension and brakes.
As part of suspension work had to pull radiator, so when refilled I started it up and it idled fine so got to temp and shut off. Refilled radiator next day and started it up. Idle zoomed to 4000 rpm.
Been emailing with Matt Cramer who has been extremely patient and helpful for a novice like me but so far no solution
Took off IAC and bench tested and all was good. Solenoid worked and 10 ohms across terminals. Got another loaner IAC and tested and got same results. Installed loaner and 4000 rpm.
Test across IAC wiring connecter and always 12 or more volts
A friend who knows a lot more than me offered to help diagnose. We installed a 2 year old open loop tune and got same 4000 rpm
My friend took a video of him changing settings while I measured across IAC connector. Nothing he did resulted in any change of voltage – 13.9 to 14v with car running and IAC disconnected.
With the IAC unplugged will it idle normally or go to 4000?
Every time I've had a crazy high idle like that it's a big leak on the intake manifold. For 4000rpms it's going to be big, like the brake booster line or something. Obviously that's not the issue if it idles low with the IAC unplugged, but just wanted to clarify since it wasn't clear in the post.
and I should have said I disconnected the brake booster vacuum line and plugged it at the manifold and no joy there either
with IAC plugged in, I manually covered the inlet port with rubber gasket material held in place with fingers, had someone else start the engine, idled normally
relaxed the tension on my finger and big sucking sound and 4000 revs
have you done the iacv test and determined the actual valve range?
many older Miata's the valve flips out if you're far out of it's range and starts pegging open or closed
also make sure you're using the right frequency because different units and valves use different ones
I read thru that and not sure it is applicable for my application
it discusses stepper valves 4-wire and 6-wire that can move in two directions
the Miata is a PWM 2-wire and is not a stepper per DIY --- "To determine if it’s a stepper or PWM valve, find the valve on your engine, it will be attached to the intake manifold, either directly or via a hose. How many wires does it have? Generally a PWM valve will have 2 wires, sometimes 3, and a stepper motor IAC will have 4 wires, sometimes 6. The MS2/MS3 stepper circuit was designed with GM/Jeep valves in mind, however it works great on many different stepper IAC systems, including most all USDM, Euro, and Japanese vehicles that use steppers, among others."
Under Idle Control, in my early release PNP2, I have the Algorithim options:
On/Off valve
IAC Stepper Moving Only
IAC Stepper Always on
PWM Warmup
15 minute IAC
PWM Closed Loop
IAC Closed loop moving only
IAC Closed loop always on
And to test the IAC circuit,the link says to turn the "Idle valve type" to "none" but I don't have that option. Only to set Algorithm to "none" Is that the same thing?
And the link shows a Programmable On/Off Outputs as having Stepper Out 1 and Stepper Out 2. I don't have those options but do have "PTC6 - IAC1" and "PTC7 - IAC2" Are those equivalent?
For your purposes, ignore everything but the instructions on finding the range, the low and high numbers, the screenshot of the menu you already posted. Once you figure that out, input it into the closed loop screen. Make sure none of your other settings (like initial valve duty table) are outside this range.
That will be a good start.