1990 2.3L automatic - real bad engine sputtering

My 1990 2.3L automatic with electronic(?) overdrive has just under 240,000 miles. I recently had problems with a spark plug constantly missing, and, I replaced the plugs, wires, and, air filter. Immediately after that, I started having really bad sputtering (not really sure if the problem existed before replacing the plugs). It happens both when the engine is hot or cold, rarely when idling in Park, and, about every 5 seconds otherwise. When it stops the sputtering while driving, it seems to be downshifting. I can eliminate the sputtering by flooring it, and, sometimes I can find a cruising sweetspot - but that only lasts for a few seconds. When idling in Drive, the RPM's go down to close to 500 and occasionally will stall because of the sputtering. When I rev it when in Park, I typically get plumes of black smoke (I do not have white smoke at all). I replaced the fuel filter, but, nothing changed. Even with this sputtering, I am able to get it up to 80MPH and the engine sounds great when not sputtering. Also, the "check engine" light is on, but, I cannot say for sure when it started lighting up (it is kinda behind the steering wheel and not very bright). The only thing I have added to the gas tank recently is something that is supposed to help burn off water in the gas tank. When I stop and get out of the car, I smell a lot of gasoline (and my allegies typically prevent me from smelling almost anything). I left it with a shop that advertises that it works on older cars, but, after 2 weeks they could not figure it out. I have been using 100% gas (ethanol-free) for at least 5 years now. I have used synthetic oil, filter, and, Lucus oil treatment for at least 10 years. My gas mileage has gone from 25 miles/gallon to 10 miles/gallon. I have owned the car for over 20 years and there has never been any work done on the engine.

After that shop couldn't figure it out, I went online looking for any ideas that might be causing it and I came up with this list of possible causes:
- fuel pump
- fuel pressure regulator
- O2 sensor
- TIF module - sputters when engine is hot, but, not when cold
- PIP sensor
- MAF sensor and vacuum hose
- fuel injector cleaner
- coolant sensor
- cooling fan module (E7ZB-8C609-AA)
- vacuum modulator on the transmission
- catalytic converter clogged
- ECU
- ignition coils
- leaks in the intake manifold gasket or vacuum hoses
- Exhaust Gas Recirculation (EGR) valve
- trottle position sensor (TPS)
- engine timing problems

I am no means a mechanic, but, I have worked on my cars for the past 40 years. So, I feel confident in being able to do some of the easier repairs that don't require special tools. Of the things listed above, I don't recall fixing/replacing any of them and I have never had this sputtering problem before. Some of those parts listed above exceed $50, so, I don't really just want to replace each of those parts without knowing that it is a good risk/try. Initially I am most interested in the "cooling fan module" because I don't think that my fan comes on at all (and the fan itself has been replaced). Also, this is my only car at the moment, so, I am not really keen on leaving it with a shop for 2 or more weeks again.

What type of experience have y'all had when encountering this problem? What are some other possible causes/solutions? If I were to take it to a shop, what would be a reasonable amount of time to expect them to be able to fix this problem or give it back to me?

Noobz347 said:

You need to pull codes.

Read the entire thing before trying any of it: https://stangnet.com/mustang-forums...des-from-eec-iv-in-86-95-5-0-mustangs.889006/

The [cheat] version is to just buy the damned code reader (kicks the podium). They're cheap and you should have one anyway.

Here's an Amazon link: https://www.amazon.com/INNOVA-3145-Ford-Digital-Reader/dp/B000EW0KHW

Click to expand...

I have that device but it is not showing any codes. This was the first time that I have used the device, so, I am not sure if the device or the car's plug is defective. Sorry, should have put that in the OP. And, I have not taken it to a parts store yet to see if their device shows anything.

Noobz347 said:

That's a pretty good indication that the EEC is bad.

Go through the instructions one more time and take a look at this video:

If it fails to test then I recommend this as your next step: https://www.theecuexchange.com/

It's only 34 years old

Click to expand...

Again, I have that device and it is not showing any codes. And, I have tried multiple times.

They are a 9 hour drive away from me. And, about 60 gallons of gas at 10 miles/gallon.

Noobz347 said:

That's a pretty good indication that the EEC is bad.

Click to expand...

In searching for that part, I came across a replacement for the EEC Test Plug Connector for around $25. I am guessing that it would be a good thing to replace that if I determine it and not the OBD device is defective.

General karthief said:

Wow, what a dance, pardon me, look you are getting advice from members here that have 'been there, done that' more than once, while there is a chance the scanner is bad, there is an alternate test using the check engine light. Regardless I send ALL the computers I have dealt with
to the ECUExchange

Home - ECU Exchange

ECU Exchange specializes in the re-manufacturing and repair of engine control modules.

www.theecuexchange.com

Only takes a week or two turnaround.
If the computer cannot process the given info it can't make things work in harmony. A poor running engine will seem to smooth out at higher RPMs because things happen faster.
Let me ask:
Did the shop check for codes? (That's the first thing done during a diagnostic exploration)
Vacuum readings?
Fuel pressure?
All these things are covered in the chacklist.
These cars are not that complicated. You don't have to be a certified technician to work on them.

Click to expand...

OK, I am a bit confused here. What do you mean by "there is an alternate test using the check engine light"? And, regarding sending a part to The ECU Exchange, basically I will be without my car for 1-2 weeks. That is not really different from leaving my car at a local shop, right? Plus, in that scenario, they are only testing the item(s) I ship to them. Wouldn't it be better to take it to a (good) shop that can test multiple items at a time?

Concerning the shop and checking for codes and those other items - they did not tell me and I did not ask. Of course, I expected them to do that since they promote that they work on older cars. Since I am assuming that my OBD device and the car are NOT communicating with each other, at this time my assumption is the connector is bad. I stopped by several shops today to see if they could hook up an OBD I device to prove whether or not the connector is bad - but they did not have that device. Clearly nobody can pull the codes if the connector isn't working and/or I can't find an OBD I device that works. Therefore, verifying that connector is now the highest priority.

Yes, I am disappointed in that shop's failure(s). And, that is why I am taking a more active role in figuring out the problem.