Car hesitates and sometimes stalls after reach operating temperature. on 1993 Oldsmobile 98

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After the car has reached operating temperature, the care will hesitate and sometimes stall when accelerate hard, stomp on the pedal. It doesn't do it if accelerate slowly, less then halfish throttle. It also will try to stall when braking heavily. These problems do not generally occur until after the engine is above about 180 degrees. It is the 3.8l non-turbo engine. I have replaced fuel pump, TPS, computer, mass air flow sensor, all vacuum leaks, spark plugs, and checked the wires. The only other thing I can think of to check is the actual fuel pressure, no gauge of my own, and the fuel injectors. I also have pinned out the diagnostic port to check codes and only ones I got were fixed with TPS and computer switch replacement. It also gets worse the lower the gas is. Any thoughts or suggestions are greatly appreciated!
(2) Answers
(4) Comments
Check for water in gas!..... Pull fuel filter and check..... Water should be in it ... IF present!
Sorry. I forgot to mention that replaced the fuel filter, air filter, oil change and filter, and pcv valve with no change. This problem has been going on for about 4 or 5 months now and was still driving it, just made sure was going to be sitting someplace for awhile after got there so the engine could cool off before heading back home so has been thru lots of gas. I also have added fuel injector stuff to tank along with octane booster, different tanks of gas, to try to make sure wasn't water in the fuel.
Hit gas...hesitates ....hit brakes...stalls...damn sure sounds like water 'sloshing' in tank and pump picking it up to me!!.... Throw an ignition module and crank sensor on it too.... You've replaced everything else!!.... IF problem still persist... Have the computer SCANNED!!!
I have a 1991 Olds 98 with the exact same symptoms! I found this site while researching my problem. I was going to check the TPS, but it looks like that may not solve the problem. My car never feels like it's going to stall while at idle, although the idle is slightly rough. Like you, if I accelerate smoothly, things are OK, but if I push down on the pedal around 45 mph or so, I get a hesitation and can actually hear a small backfire if I push really hard. After I slow back down, I'll do it again and it seems OK. About 2 years ago I replaced ICM, coil, plugs and wires, so I figure I have the spark side of the equation covered. I'm close to giving up and taking it to my mechanic and paying $115 to get it diagnosed. If I do, I'll report back. I'm figuring a fuel problem this go 'round.
I am about to the point of taking it and getting it checked out myself. I got a loan-a-tool fuel gauge and checked and pressure is good, as well as checked the plugs and coils and they were all fine. Is there any chance the transmission could be causing it? I checked the fluid level but haven't changed it myself and owned it for about 3 years now. I only even think about this because noticed the other day when was trying to duplicate the problem and wouldn't happen until after drove on the road. I let it run sitting until the fans kicked on and the temp gauge was just below 200 and still wouldn't duplicate if gave it throttle without it in gear. Just wondering if I might be looking in the wrong area for a problem. I am planning on changing the fluid and filter in the transmission on my next check and seeing if that helps any.
I have an appointment tomorrow at 8 a.m., so I'll let you know what I find out.

Update: 8 July 2014, 1245 pm

Took the car to my mechanic and was told that my spark plugs were finger tight. They recommended replacing all the plugs with AC/Delco platinum and replacing the wires with a premium set. Also recommended the carbon flush, which I did a few years ago with no appreciable difference. They did check the fuel pressure and it was fine. I came home and figured I'd tighten the plugs and in doing so, I broke off the end of one of them. I got a ride and bought one plug, came back and promptly dropped it. Spent 30 minutes looking for it and never did find it. It will be on the road one of these days. After gapping and replacing it finally, it does seem to idle a bit more smoothly, but still has a hesitation when I get on the gas. Not as bad as before however. I tightened only the 3 plugs toward the front of the car as they were a lot easier to get to, plus I have a doctor's app't this afternoon at 2 so I need to shower and shave. My plan is to get some premium plugs and wires and replace all 6 and see if there is improvement. FWIW, when I was having problems before, the mechanic had to replace the wires that come out of the Ignition Control Module. I tried an after-market ICM, but it caused a Service Engine Soon light to come on, but an AC/Delco ICM fixed that problem.

Update: July 11,2014

I replaced the plugs and wires and it appears to have done the trick. Idle has smoothed out and there is no hesitation when I get on the throttle. I used NGK Iridium IX which came pre-gapped to 0.060". I carefully checked the gap on each one and used anti-seize on the spark plug threads and some di-electric grease inside the spark plug boots. As you know, the plugs on the firewall side are a bear, so I don't want to have to change them again for a while so that's why I went with the iridium. From the research I did, they are a lot harder and thus won't erode as quickly as copper. Sure enough, though, I was able to remove some of the plugs with just my fingers. I'm quite certain I torqued them pretty good when I put them in. I am hesitant to over-torque so I wouldn't break the porcelain portion or mess up the threads in the engine. I don't recall if I used anti-seize last time, but if I didn't, I don't see how the plugs would be so loose. Maybe I didn't let the engine cool down enough last time, but I don't recall burning myself. I have never heard of having to re-tighten plugs after so many miles. The mechanic did tell me that the Champions I had put in weren't the ones called for, but that's what the guy at the auto parts store gave me. I had already blown my budget on the ICM, coil, and the re-wiring of the harness to the ICM so I had to go cheap with the plugs and wires. The wires, after removal, looked OK, but I replaced them anyway. I had only one boot stick to a plug this time and tore out the wire, but figured new wires would eliminate any problem with one that I just couldn't see upon inspection. Seems like my problem has been solved (fingers crossed) for now, but it looks like you've already done plugs and wires. If you ever figure it out, please post as I may be going down the same road one day.

Update: 13 July 2014

My car is still running fine. After looking at your original post, I didn't see that you did anything with your Ignition Control Module. As I said earlier, my mechanic spliced new wires that come out of the ICM which helped for a while, but then the problems with stalling returned. A new AC/Delco ICM did the trick. As I said, I tried another brand at first which caused the SES light to come on. I'm told that GMs love AC/Delco parts. Try the ICM and I hope that does the trick.