Thanks for your input...
By chance have you checked for a clogged cat or partially clogged cat?
I can check it, but I don't think this is it for a few reasons. I experienced the issue when downpipe had a rusted out hole in it, but I have since then replaced the downpipe. Also, the current motor has very, very little oil consumption, and the fuel economy has been better than ever, so I assume I am not running rich.
It wouldn't hurt to check though, if the bolts are not too corroded, I will take off the cat and check it out.
Same for injectors. inspect your spark plugs closely for any signs that something is off.
I plan on checking the injectors out, although when I removed the last set of plugs, they looked fine. Looking at the plugs at the time of symptoms is very unrealistic for me, so I will have to figure something else out.
Only other thing I could possibly think of off hand is maybe ECM.
I thought of this. Having multiple random issues seems similar to a Ford truck I owned a while back.
I had a bad ECU on an old Ford. It started out with occasional random CELs looking like sensors were bad, I would test them and they would be fine. Most of them I replaced because they were so cheap on the Ford. After a few months of this, I started getting multiple CELs, many of them not making sense. I suspected the ECU, but many people in the forums said stuff like they never go bad. I got a refurb for really cheap on Ebay, swapped it, and it ran better than ever.
For the P5, I am not sure where to start with the ECU, maybe I will take it out and check to see if there is any obvious issues.
Hell, it could just be a loose or corroded ground wire somewhere that's killing injectors or ECM or something and causing it to stall even.
I double checked the grounding strap to the motor over the weekend, it was there, I check for continuity and had it. Maybe I will test for the resistance.
I thought of possible grounding issues due to the motor swap from a few years ago. But, I guess it could be another ground somewhere... Most of the grounding points are corroded, so this could be a problem.
On another forum I use, people talk about grounding issues a lot. On the MR2, grounding issues often lead to fires. Many times grounds are forgotten during motor swaps, and it sometimes causes fires. I think due to the battery location.
I'd personally ignore everything you've done up to this point and start from a clean slate.
I kind of been doing this all ready, although everything else I have done seem to make the P5 run better. The new fuel pressure regulator got rid of the CEL I was getting, but didn't fix the stalling and power loss issue. I feel like the P5 generally runs smoother and doesn't have the hesitation since the fuel pump/filter change. Changing the pump/filter was a huge pain, but only because the screws on the retaining plate on the filter assembly were so corroded that I had to drill every one out. But, @ 150k, I think it needed to be changed.
Some of the stuff that has been done so far had little to no positive effect that I have noticed, but it also was little cost and effort from me.
As for the compression, I have a kit, I might check it this weekend if I have time.
Thanks for all your input.