Computer diagnostic?

[MoreMayhem]

I've been chasing a couple engine problems with my car: low idle, off the line stumbling, WOT hesitation.
I've read many threads here and on the wilds of the interweb, followed the procedures provided by Robert Bentley, replaced 90% of the items with a wire that are attached to the engine, home-made smoke tested and repaired leaks, and have just lived with it for months.
I stopped by an independent european shop today, and they suggested a computer diagnostic. I asked if it would show any more info than what is stored in the dme and displayed during a stomp test. Guy said it would. I have my doubts, so wanted to ask here if there is any validity to doing this procedure? Don't want to part with my hard earned dollars if it isn't worth it.
Apologies if this has been discussed previously, my feeble search attempts revealed nothing.
Oh, forgot to say: 1988 with stock M20B25.

[jlevie]

The DME on these car is pretty primitive and all a diagnostic scan can to is to return any stored fault codes. But you can do that yourself with a stop test. I have my suspicions that your "home-made smoke test" was inadequate as most of the symptoms described are consistent with intake leaks. The WOT hesitation probably isn't from intake leaks and could be from a bad WOT switch in the TPS or a bad AFM.

A proper smoke test consists of plugging the exhaust, replacing the AFM with an adapter for smoke injection, and holding a smoke pressure of 2-4psi for at least 5 minutes. The smoke must be a long persistence oil fog that will last long enough to reach leaks distant from the intake.

[James Crivellone]

DIS/GT1 can read the factory DME without any issues, not sure about other options

[MoreMayhem]

Thank you for the responses. I didn't plug the exhaust any of the times I did my diy smoke test. I did remove the AFM and made an adapter to seal the rubber intake elbow and introduce the pressurized smoke. What I'd the best/easiest way to plug the exhaust? That will be my next step.
Also: last night I pulled the plug wires 1 at a time while the engine was idling, and it seemed I didn't get any noticeable change in the engine running condition on 1,3,5. Disconnecting 2 and 4 made it run worse, 6 killed it.
I used an inductive timing light on each spark plug lead at idle and got a flashing light for each one, tested continuity and resistance on each spark plug lead, and listened for tapping noise in each injector with a long screwdriver. Everything seemed okay. Feeling kinda lost.

James, DIS/GT1 can read the dme, but does that mean it can read more data than what a stomp test can show?

[MoreMayhem]

Upon further investigation, my last observation about unplugging 1,3,5 not having an effect on idle speed was not correct. Maybe I didn't pull the spark plug boot far enough away to stop the plugs from firing.
I narrowed it down to cylinder #5 being the possible problem.
I pulled all the plugs and 5 was definitely more fouled than the others.
Next I did compression test. Lowest was 175, highest was 185. Pretty good, I think for 241xxx miles.
I cleaned and gapped the plugs on the tighter side of the range listed in the Bentley. I had previously gone on the wider side of the range. It seemed to run much better, without any off idle hesitation, or WOT hesitation.
It was fun to drive again!
I think I may still have some underperforming injectors, which is disappointing as I bought what was supposed to be a refurbished and flow-matched set.

Also: mods feel free to move this to the M20 section, where it probably should have been in the first place