The car: 89 Sidekick with a 94 Tracker, 1.6 L 16 valve engine installed three years ago. The "old" auto tranny was swapped out for a standard 5 speed too.
When cold and coming up to a normal operating temperature it idles fine, but once it gets thoroughly warmed up the idle drops down to 200 RPM or even zero (on the tach) and it will die out. Sometimes if I use the go pedal to keep it running for a minute or so it will then idle OK on it's own (sometimes!).
A friend in another state said he had a similar problem and he replaced the fuel pressure regulator. Is that maybe what I should be looking at ?

You might check the throttle cable for wear as it goes thru the
firewall and if that checks out OK, see if you can just turn up the
idle with the throttle stop screw.

Before changing the FPR, check your pressure, should be about 36 PSI

Wild

Check your timing too, if it's retarded at all your idle will drop as well. The standard tune up stuff should be checked as well, especially the air filter, old dirty filters make it harder for the engine to breath, and old fuel filters can make your pressure drop.