Thread: Bad missing, very low power, almost undriveable

Here it goes (1994 Pontiac Grand Prix standard 3100 SE V6 motor)

History: Car ran fine, but we had three vehicles and I let it sit from about 4-6 months with a battery tender on it. Lost a vehicle since, so we had to start driving it again. Cranked it up and running like garbage (missing, almost no power on acceleration, no service engine light). Crazy side note - A/C is cold but on the very weak acceleration, the plenum doors for A/C will cycle down to floor and then to defrost on their own. Let up acceleration goes back to where it was set - dash vents. It seems tied to engine problem which started me down the vacuum route.

Steps already taken, numbering, in chronological order (I am now somewhat at a loss as to what this could be):

Air/Vacuum:
2. No noticeable leaks audibly or visually in or around top of engine. Plenum has pretty descent vacuum at all ports.
3. Changed air filter - cuz it needed it and was time
4. Whole can of carb cleaner sprayed in at throttle body
8. Finally, was able to clean completely clogged EGR port on plenum that was throwing intermittent EGR code for about 3 years, LOL. EGR valve was replaced about 50,000 miles ago for this and didn't fix that.

Ignition:
5. Changed spark plugs (needed it - posts worn to .080+ now at .060 - didn't fix main problem)
6. Changed plug wires
Note: Inductive timing light seemingly indicates some missing, but doesn't appear drastic

Fuel:
1. Two bottles of fuel injector cleaner in full tank of gas
7. Pulled fuel injectors, manually cleaned using pressurized kerosene and carb cleaner with injectors open on home made test bench with a switchable 12V battery. Spray pattern improved to what looked like acceptable to me. All solenoids worked. Forgot to ohm them out - shame on me.
9. Removed and cleaned throttle body thoroughly
10. Reinstalled injectors with new o-rings on both ends of injectors
11. Replaced fuel pressure regulator with new o-ring
12. Replaced o-ring on fuel rail return line
13. Reinstalled plenum with new gasket
14. Reinstalled throttle body with new gasket
15. Replaced PCV valve, intake grommet, and purge valve fitting on hose
16. Replaced rear valve cover grommet that snorkle hose fits in
17. Replaced MAF sensor
18. Replaced fuel filter
19. Took fuel pressure reading from rail fitting while engine was struggling 40 PSI on the money! Fuel pump seems OK, plus I can hear it prime when key is turned
NOTE: When I got done the fuel steps, now the idle sits around 2k, new added problem it seems.

I am pretty frustrated at this point, can't afford dealer repair costs. Only things left that I know of would be:

-O2 sensor - I don't believe it can cause an engine to run this bad and was changed about 80,000 miles ago
-IAC
-TPS
-Coil packs (gonna try the ones in our '98 Intrigue running well)
-Elec ignition module
-Fuel injection signals
-Possible vacuum leak in dash - A/C?
-Knock sensor?
-EGR Purge valve?
-ECM/fusebox/wiring?

The engine/car is worth getting running well again without dumping tons of money back into where I could get a newer vehicle for 4-5k. It is just so weird that it was running perfect, sat for a little while, and now barely runs! UGH! at wits end, please help!

NONE OF THE ABOVE! Turns out I did a fine job cleaning injectors that were partially to fully clogged, and doing preventive maintenance on much needed components. However, when I replaced the spark plug wires I crossed #3 with #5!!!!! ROFL, I even changed them out one whole wire at a time to prevent that, but then I went back and re-routed a couple due to the varied lengths of the new set of wires, and that must be when I crossed them. Talk about trying to chase that down when you are that confident you didn't cross any of them! The only motive to go back and check my work was a friend told me a neat way of checking the coil packs - remove two wires off a pack (making sure not to cross them - had to throw this in here), and crank engine to see the spark arc between the two posts, and then repeat for the other two coils! What clued me in was when I tested the outter two coil packs this way the engine was able to stay running, but when I tested the middle pack, the engine fired, but would stay running without starter engaged. This was suspect to me that 4 firing pistons are enough to keep engine running except the middle pack combo??? Just didn't add up, so I checked wires, and wala, it all made sense.

Crazy other observation is that the vents for the A/C system were starving for vacuum with clogged injectors first, and then later the crossed plug wires causing the cycling of the air to the floor and defrost vents on acceleration only, and then back to dash vents when coasting. The engine was not running efficient enough either time to provide enough vacuum to keep the vents in dash position. Vacuum charts confirmed this, because that combination of vent postions requires the most demand for vacuum! CRAZY!!!

Oh well, it was all worth it in the end!