I have started having problems with my 1994 convertible. I'm pretty sure it's the optispark dying, but i want to get ya'lls opinion before I start a repair that's going to cost so much.

Sequence of problems.

Car had been running great, then:
After three weeks away from the house (US Navy Submariner) I came back home and installed a CATBACK exhaust.

Another two weeks underway and I come back to the car having a rough idle. She would surge between 800-1600 RPM when idleing (meant I had to put it in neutral sitting at stoplights).
In responce I used some throttle body cleaner, which helped bring the idle down to 800-1000 RPM.
(Probably unrelated) left turn indicator has stopped blinking, changed the front turn indicator, whick seems to be the problem, and didn't fix it. That's another (less problematic) line of troubleshooting.

Yep, another week underway... That's when the problem really started.
Symtoms:
Hard start: 10-15 sec of cranking till it starts (wasn't even a problem when I had to leave her for a month and a half last year)
Very rough idle (500-2000 RPM surges)
Bad stuttering durring acceleration, WOT was horibble,
Durring acceleration to highway speeds (heavy stuttering), the tackometer dropped to zero, followed by a backfire (sounded like it was under the hood) and the service ASR light.
And that led to the early return to the garage at home.
Pulled codes (diagnostic mode) and got 4.H36 and 9.H62.
Followed the FSM for DTS 36, Code came back, 5.03V at the high resolution connector at both the test connector and at the distributer.

Seems to lead to the OptiSpark. This is especially disterbing given that the previous owner changed the water pump and optispark to get the car running again from the previous previous owner.
I don't see any indication of water pump leakage, or water under the hood.
Any suggestions for additional troubleshooting/things to look at?
The next question becomes, if it is the optispark, what did I do wrong?
Any suggestions for changing it out? As much as I would like to do the work myself, I will probably have to take it to a mechanic due to a lack of time away from work. This is an even more expensive prospect since I am in Hawaii, which means that everything is more expensive.

Thank you for your time, and any help in advance.

 

May be false air/leaking manifold or such. I would first spray a little starter fluid around the intake manifold while idling and see if rpm surges. Opti, in my experience, either works or it doesn't - no surging.

 

I had all the problems you are having except the hard starting. My problems started at 62000 miles on my 94. I replaced the coil, opti-spark, plugs, wires and the water pump.
It has run smooth thru 84000 miles.
Guys on this Forum say using water to clean the engine is not a thing to do.
I did the work myself with the help of the forum and the red repair manuals.

 

Have a look at the vacuum line for the FPR just to make sure it is not leaking.

Also have a look at the IAC. Clean the plunger and where it seats. Lub the assembly, make sure it is not sticky.

Make sure other problems are not compounding your initial symptoms.

 

check manifold vaccum with gauge. You did have a 36 alarm which is High Resolution on opti. I had a bad opti with a 36 alarm for way over a year though and the car ran fine under normal conditions until I finally got around to changing the opti.