I have a 1991 240SX that developed a hesitation problem literally at a red light. Everything was fine until I stopped at a light and when I went to take off, it didn’t want to go. I had to feather the gas just to take off. After I got going I could floor it and RPM’s went up, but It acted like it was starving for gas. I changed out the fuel filter and also changed the plugs, no change. I then thought it might be a clogged injector and ran a couple of bottles of cleaner, but no change. All the injectors are working. Thought it might be the MAF, but that seems to be OK. I did clean it just because and no change. I had put on a TPS about a year ago because of another problem and I don’t suspect it, but I looked at it anyway, it checks out OK. I checked fuel pressure and it is within specs. I am wondering now if my spark is hot enough. I realize the answer is probably going to be, “Could be anything," but I thought I would see if anyone had any idea what could be causing this hesitation problem?

How did the plugs look when you pulled them? Usually that will point you in the direction you need to go.
Also, check your engine grounds. Weird stuff can happen when those corrode/break. The one on the driver's side rear of the head (above the exhaust) seems to be the most susceptible to letting go.

The plugs looked OK, nothing crazy, but since I had already bought new ones I replaced them. I haven't checked all grounds, but I know the one on the TPS is good. I could look at others. Thanks.

Didn't have much of a chance to look this weekend, but that ground is OK. Also there is another one beside the braided one that bolts to the block and goes wherever and that one is good also. I made sure there was continuity to the frame and also back to the battery. Not sure why that braided one has a push on connector instead of bolting directly to the firewall. Seems like bolting would be more secure.

I wonder if your secondary butterflies aren't opening or something. I think Nissan called it a "swirl control valve" or something that operates them. Supposed to increase turbulence at idle/low RPM for a better burn.
I removed mine and haven't had any issues. They are located in the intake manifold and controlled via a vacuum actuator IIRC.
Does the engine rev seemingly normally if its sitting in neutral? IIRC, you can manually open the valves by pulling on the lever from the actuator. You could try opening it and revving, or zip-tieing it open or something and going for a drive.
I don't suppose you have access to a wideband O2 sensor do you?

When in park it still hesitates when I punch the gas. RPM's will go to redline eventually, but it struggles. I don't have an O2 sensor. Years ago I had a 2004 Xterra. It developed a problem that I thought might be a stuck injector or something. Came on all of a sudden also. I was by the parts house and pulled in to get some injector cleaner. I then got on the highway to kind of blow it out. As I was going it was like turning the key off and it just quit. I had to call a tow truck to take it to the shop. Turns out it was the distributor. That was kind of making me think it could be spark related. I don't want to change distributor on a guess though.

Yeah you could check base timing, pop the cap off and just see if the contact points all look ok, but I would imagine your plugs would have looked terrible if that were the case, and it would also sound a good bit different/exhaust would smell.
The slow rise in RPMs is what's making me think its some kind of restriction somewhere... either intake or exhaust (like a clogged cat or something).

Where is that butterfly thing located? I looked over the intake and don't see anything like that. I know you aren't talking about the throttle body are you, since that valve connects to the pedal and I know it is working?

I started thinking I had a clogged cat. Started looking at some Youtube stuff. Engine light doesn't come on but could have the symptoms of a clogged cat. I saw one video that said a quick check would be to measure the temp before and after the cat. If it was higher in the front than the back that would suggest a clog. My temp is lower in the front compared to the back so based on that maybe not a clogged cat. Could it be the O2 sensor?

The secondary butterfly valves are located inside the intake manifold, but the rod/actuator comes out the back, near the firewall.

The actuator is 27655Z in that picture.
This doo dad right here: