I'd hoped replacing the lazy, upstream O2 sensor would have eliminated the hesitations, but no joy. Immediately after replacement, starting and idling for 2.5 minutes per drive cycle requirements, I'm still getting hesitations every 3-5 seconds while idling and cold. Yes I'm still waiting for the P0410 code to clear itself.

So I may have had some confirmation bias on the brain in the replacement of the plug wires making the engine run wonderful again.

Subjectively the acceleration seems snappier. I'm not getting hesitations on quick acceleration. The acceleration is responsive whether AC is on or off.

 

I'm still getting hesitations similar to what I might equate to real time engine ping adjustments—BUT IT'S HAPPENING WHILE IDLING! So it can't be pinging.

I'm running premium fuel. I had run a bottle of fuel injector cleaner through the last tank of gas, but that's been driven to empty and refilled, so I have fresh fuel in the tank. The P0410 code is not clearing itself. I'm also still showing an EVAP failure on my emissions tests. It's the only remaining emissions test failure.

New upstream O2 sensor. New plug wires. NGK plugs from 2 years ago. New throttle position sensor TPS. New idle air controller IAC. New crankshaft position sensor CKP. Secondary air flow confirmed working and air pathway confirmed open up to where it enters the exhaust manifold. When I watch the real time data on my OBD Android bluetooth app, I'm not seeing anything yet that would identify the hesitation coming from something I'm looking at at the moment. I can customize the screen to display other sensors.

Could it be a ping sensor adjustment, even though it's hesitating while idling which makes pinging be an unlikely cause?
Does the exhaust manifold need to be removed to confirm the four air intake paths are not clogged? I can dig up the
Do I bite the bullet and say, “Come on… it's a 25 year-old car. There's going to be a hiccup here 'n' there…”?

Seeking some ideas for direction or things I may not have checked that need checking. Thanks.

 

I guess it's a stupid question since I'm NOT a mechanic, but could this be related to the EGR?

 

P0410 is still your secondary air system. There is a diagnostic tree on charm.li that explains how your car determines this failure. It looks for a lean condition while the air injection is running to verify proper function.

Your evap monitor not completing is unrelated. I would diagnose separately.

Your running issue may be part of the P0410 trying to self diagnose or not.

I am not much help with this, sorry.

@grcauto8453 ?