I am fighting with an issue with a Flyin' Miata Turbo'd '99 Miata running a DIYPNP. I am getting random return to idle issues. Does not seem to matter hot or cold engine. If you just unload the engine, just push the clutch in, while coming to a stop, it will do one of three things. It will sometimes drop into a very nice idle, running 14.8-15.2 AFR's. Sometimes it will drop into a rough idle and running at 10.0 AFR and stumble. Most times however, it will go super lean, stumble and die. If you keep load on the engine, slow down without pressing the clutch until the engine almost dies, then push in the clutch, the engine will some times idle like normal. This is not my first time tuning idle as I have set-up multiple Megasquirts to idle with Miata idle valves, including this DIYPNP in my own '99 prior to upgrading to a MS3 Pro, but this has me scratching my head, big time.

I have replaced the cam sensor already in diagnosis, but no improvement.

Here is the MSQ and two data logs.
2019-06-24_20.19.42.msl
2019-06-25_17.47.57.csv
New Throttle Body 6-3-19.msq

Any help would be gladly appreciated. I am also chasing a boost control issue, I cannot get the Mac-valve to respond, but I need the car to idle correctly before I can begin to worry about making more boost.

 

No one has any ideas? This is driving me crazy.

I am thinking I might try swapping out the injectors. Maybe the injectors are getting sticky at low flow rates, sticking open causing rich, sticking closed causing lean, etc. The car owner tells me this was doing this before we put the Megasquirt in the car.

 

Which throttle body are you running? I’ve noticed with my skunk 2 about 1 in every 20 times I go to idle and let off the gas the throttle body slightly sticks and keeps it ever so slightly open leading to a higher idle. I’m planning to use an additional spring to make sure it’s closed.

Also check the slack in the throttle cable to the throttle body

 

Stock '99 throttle body. TPS values show the TPS fully closing in all the data logs. Thanks for the suggestions.