I'm finding myself with more time in the evenings because, well, you all know why. I've been using some of it to resolve my 1993 Miata's intermittent rough idle at startup. It's been an issue the entire time I've owned the car. Worse on hot days and/or when the engine is heat soaked (ie: I park to pick up a few groceries, letting the car sit for ~15 minutes).
This seemingly minor issue has taken me on a magical mystery tour through the entire air/fuel delivery system. I've cleaned the mass-air flow sensor, throttle body, and idle-speed control valve; checked the purge solenoid for the charcoal canister and fuel pressure regulator; changed air and fuel filters. Next up: fuel-pump pressure checks and, perhaps, fuel-injector replacement. And a bottle of Techron because why not?
What gremlins are you all chasing? Am I the only one who both loves and hates the challenge of hard-to-diagnose problems such as these?
Much like you, I am interested in tackling these troublesome issues since I shouldn't be going anywhere after work. I bet your issue are worn out/clogged injectors, definitely check your fuel pressure (when the motor is cold and hot) but don't bother with the magic bottles of fuel cleaning.
My current crop of problems are electrical, I found one of them to be because of a bad ground. I could never find the place where the ground wire failed, and I'm not removing a dashboard to find it, so I added two extra ground wires (going to a shifter bolt that goes into the chassis) and it solved my problem. Now I think I will do that same thing to another car with a seemingly impossible to fix ground wire issue: sometimes it just takes a victory to motivate you to tackle more projects.
Oh, yes. I've been inspecting/cleaning/tightening grounds, too. Probably has nothing to do with my issue, but can't hurt. It's odd: I probably spent just as much time wrenching previous years, but it seems now I have more patience for nagging, thankless tasks whereas usually I'm just bolting on something that will (theoretically) make the car faster.
Any do-at-home test for the injectors, aside from making sure they're indeed ticking? Replacements are relatively cheap, so assuming the fuel pump pressure is in-spec, I'll try that next.
Aside from taking a stethoscope at each injector and waiting for the click sound, I don't know if any of the injector tests will help with your issue (mostly for check engine lights). I assume there is a fuel pressure or spray issue that only happens when things get hot, and at this point (and considering rebuilt ones are CHEAP) I suspect the injectors are just running poorly. I have changed injectors for this reason twice and been happy with the results. One time I gained 2-3 MPG, which was an added perk.
Have you done a voltage check on your tps at closed and wot? You should also be able to get a resistance spec as well which would allow you to unplug the harness and adjust it if out of spec. with the key off.
I have had more than one car with an out of spec tps send me down a troubleshooting rabbit hole.