Alright, I'm not too keen when it comes to diagnosing engine issues, so, I figure I'll ask around for some insight from others.

So, I have a 1994 Corsica with the 3100, car has 76K on it and it sat for a few years before I bought it (it was an elderly couples car).

The issue I'm having is that now when the car is started, it runs a little rough and produces some slight backfires every so often. When the accelerator is pressed, the roughness smooths out quite a bit. Driving the car around in town there seems to be no real noticeable issues, but when one tries to reach highway speeds, the car will begin to buck as though the engine is not getting proper fuel/air. The faster over 50MPH, the worse it seems to get.

I haven't done much to the car in terms of trying to figure out the issue and addressing it, but I have replaced the fuel filter, plugs, air filter, and changed the oil with no signs of any improvement. I figured all these were good to replace regardless, but I'm not about to go throwing money at the car randomly replacing anything that comes to mind.

There is no check engine light and no codes being thrown.

Potentially, I feel it could be an O2 sensor, EGR, coil/coil pack issue, but could easily be a number of other things I'm sure. For example, perhaps a blown intake gasket?

I have another car I'm driving, so the Corsica has now sat in my garage for half a year and now with Spring coming around, I'd like to continue to attempting to get the car on the road.

So, any ideas?

Can't say as I smelled any sweetness in the exhaust, though I must admit I didn't really want to bend down and start huffing my car'* exhaust. (lol) Nor did I see any signs for white smoke or anything from the exhaust.

Still, I know the intake is notorious for failing on these cars and with the age of the car as well as having sat for so long before being ran again, I'm wondering if it may have actually caused the intake manifold gasket to go.

Brandon Welcome to the forum!
Ill take a stab at this..Got a fuel pressure gauge? If so what is it at rail?
FPR fuel pressure regulator.. any wet fuel from nipple or in hose after running a while?
Ignition, how old are the wires? Check for corrosion at coil ends or consider replacing.
BAd fuel? try adding an ethanol stabilizer/water remover.
Hope something here is helpful.

Don't even bother with fuel treatment. If its been several years, dump what you can out of the tank and put fresh gas in it along with 2 bottles of injector cleaner OR half a bottle of Seafoam.

Next, replace those plug wires.

Alright, I see I may have left a little out.

After buying the car, it was soon involved in a fairly minor fender bender (just days after purchase), hit someone that pulled out in front of me at about 20MPH (estimated as I was doing 30 and hit the brake just a couple seconds before impact). Air bag was deployed, front right headlight assembly was relocated about 2.5-3" inwards and the hood, fender, and bumper got messed up. I drove the car home from the accident site, roughly two miles, and noticed no signs of severe damage. Radiator was intact, fans worked, car didn't seem to pull one way or the other. Still, couldn't drive the car legally with a busted headlight and the hood was next to impossible to open and close. So, it sat for a nearly a year until I began fixing the body damage and replacing the air bag. Well, after doing most of this, I then went to start the car. She cranked for a few seconds longer than what I remember it taking, but fired up and then immediately died. Cranked it again and she fired up instantly, but ran quite rough. Figured it was bad fuel. So, given it was sitting on less than 1/4 tank, I decided to dump some seafoam and Heat with fuel injector cleaner into the tank and dive it until it can to empty. I then filled the tank and continued to drive the car. Over a weeks time, I put maybe 20 miles on the car and the roughness of the car running hadn't changed much. So, I figured it was time to take her on the interstate to clean out the cobwebs. This is when I found out the car didn't like going over 50MPH. Still, I figured it just needed a little more time. So, I dove it at 45MPH to a nearby town and back, putting about 60 miles on the car. for this 60 miles, she seems to suck down about 1/4 tank of fuel. I was like, "What the *?!"

So, this is when I began doing the tune up and changing of the oil, spark plugs, air filter, and fuel filter. After these were done, all in the same day, i noticed next to no change in the performance of the car. She still ran as though it had bad fuel, improper fuel/air mixture, etc.

Anyways, out of frustration and not wanting to risk damaging the car any further, if damage was in fact the issue somehow, such as a blown gasket, I went back to driving my Cutlass Ceira.

Now I'm really to try to tackle the issues with the car again. Car has sat since I gave up on it last year in September and so the fuel in it "may" be going bad once again, but I feel that is likely the least of my worries.

I'm considering taking the car to a mechanic, but I'm just not so sure I want to pay $90/Hr for them to just look at the car, you know.

So on to answering your questions.

No, no fuel pressure gauge, I haven't but basic tools, for the most part. About the only specialty tools I have are ones I've bought for assisting in car audio installations. Still, O'Reilly Auto Parts here in town rents out tools, so one should be pretty easy to come by.

The fuel relief valve seemed to have some pressure after the car was shut off, I mean last year I did depress it once just after shutting the car off and it seemed to squirt the fuel about 5-6" (IIRC). Still, I should be able to check the fuel pressure sometime within the next couple weeks. Probably this next weekend.

Wires? Probably the OEMs from 94'. Or at least they probably are. After all, the car hasn't but 76K. It was the elderly lady'* car and after she passed, he sold it. If they were replaced, it was over 5 years ago.

Coil packs seem fine, they were robbed off the car when I first parked it to put on another 94' Corsica, which went to the crusher when I picked up the cutlass. Coil packs were taken back off the other Corsi and put back on this one.

So, I will check the fuel pressure and try replacing the plug wires.

Might see about doing a vacuum test as well. Some reason, I've been told by a couple people that I probably have a bad intake gasket. Not sure their reasoning, other than it being a common issue with the 3100.

Brandon, If before u stored the car it ran fine and then after storage it ran bad, The first thing I want to mention is about fuel and storage of it.
Fuel that is left unattended without a fuel stabilizer, will sour, turn to gel/varnish, and guess where it sits...bottom of the tank.
Even before u start it with some fresh fuel in tank, gunk can get through the system/into injectors++++
For the sake of a $10 bottle of ethanol stabil, when I store My Jeep for 3 months, the first thing I do is add STA-BIL, Fuel Stabilizer, Ethanol Treatment Products | Gold Eagle as it makes the fuel good for 1 entire year and relieves me of worrying about it. I also start the jeep once a week to normal op temps.
Since now ur car has been sitting for 4 months? without stabil..I would add a double dose of it now, (according to instruction on bottleX2) and then add 5 gal of fresh, highest octane fuel ASAP please, & your car will say "Thanks" I Needed That!
It also has a water remover, and believe me water can sit at bottom of tank as ethanol fuel does absorb moisture esp if car has been parked outside.
After adding the stabilizer, If I was with you, I would go though things with a fine tooth comb, new wires, pull one plug to look at running condition, Pull IAC, using throttle body cleaner same with MAF, look for cracked hoses/vacuum leaks, spray some carb cleaner around the intake base while its running to see if u have intake gasket problem. and take it for a solid 2 hour highway boogie adding to fuel:
2X http://www.techron.com/techron-concentrate-plus/
Pretty much did all of the above when I first bought the park ave & then some.
Well the good news is at least my beast is finally running right ( I Think) subject to change LOL..
I hope this may help you as well.

Checking the fuel pressure is certainly a good idea, but the first thing I would do is pull the vacuum hose off the fuel pressure regulator. If the inside of the hose smells like gas, you need a new FPR. There is a rubber diaphram inside the FPR that can dry out and get cracked from sitting too long (like any rubber can) that could be causing your problem.

had same issue with cavalier (4cyl) no back fire, just no speed turned out to be fuel pump. my 3.8 Buick had backfire and loss of speed, turned out to be a bad coil, spark was red instead of blue when I pulled wire off with it running. be careful using that method you can get zapped pretty good if you don't protect yourself.

A bad coil should light the CEL for a misfire. Did you find that when your'* failed?

no, it did not show any codes just ran like ***t.

Agree with checking the fuel pressure regulator and the fuel pressure.