My code list says: 186 = CM = injector pulse width too long or MAF too low. Quick primer (might read Glacier's primer on computer engine controls at the top of the computers, chips, tuners forum to get a basic feel for how the engine manages fuel:air mixture). The computer calculates how long to leave the injectors open based on input from several sensors (MAF, O2, TPS, and so on). A CM 186 means that, sometime during the last 80 drive cycles, the computer's calculations resulted in the computer wanting to leave the injectors open too long.
There a lot of possible causes. 1st thing I would do is perform the KOER test. These kinds of things are often easier to diagnose if they show up in the KOER test. Can I assume you got a pass 111 from the KOEO test?
A few other thoughts from reading the whole thread:
1) Automotive convention is to refer to "left" or "right" as viewed from the driver's perspective. So the "right" side of the engine refers to the passenger side with cylinders 1,2,3. The left side refers to the driver's side and cylinders 4, 5,6. Not a big deal, because you know what you meant. Just so you know, when I refer to left I mean cylinders 4,5,6; right refers to 1,2,3.
2) I find it interesting that your timing light is triggered by the left side, but not the right. The spark plugs are fired in pairs: 1 from the left side and 1 from the right side. I don't remember the exact pairings. Baiscally, if your timing light can see the spark on 5, it should also be able to see the spark on the cylinder paired with 5 (I think it's 1). Are you certain you had the timing light hooked up correctly? Are you certain of the engine ground? It's hard to predict exactly what will happen when a ground goes bad. Perhaps you have a situation where the current to the left side can find a ground, but the right side can't.
3) I wonder if a cylinder balance test would show anything. Your '94 is capable fo performing a cylinder balance test as part of the KOER test (see my notes on pulling EEC-IV codes). It would be interesting to see if the computer flags 1,2, and/or 3 as non contributing cylinders.
4) You might check base timing and timing advance. There's no provision for adjustment, but it might be interesting to see if the computer is advancing the timing correctly. Since #1 doesn't trigger the timing light, you could hook it up to #1's pair (I thnink it's 5) and see the same thing.
5) Even in this age of computer's, sometimes the best indication of what's going on in an engine is to inspect the spark plugs. Do these 6 mo old spark plugs show any funny deposits? Any differences between the right and left sides? A compression test might be interesting to see if there is anything wrong in that respect.
6) I would perhaps also suggest a fuel pressure test (see Glaciers fuel pressure mini-diary in Under the Hood). A lot of the time, one of the first tests with a fuel control code (like your CM 186) is to make certain fuel delivery is working within specs. As part of this, check for fuel in the vacuum line to the FPR. Fuel in that line=bad FPR.
That should give you a few things to look at. Let us know what you find.
