I’d say maybe bad gas? Clogged injectors? Definently sounds like a fuel delivery issue if it bogs under acceleration

Maybe try some fuel injector cleaner, and pull your plugs, a new set of ngks gapped properly, I know this is a bad comparison but every spring my lawnmower gets a new plug, new gas and I clean the carb, sure it could be any number of things but I like to start with the simple stuff

Sounds like a bad maf to me. Large throttle inputs causing stumbling or stalling is classic maf failure on alot of cars. You can get rpm by doing just what you did, small throttle inputs. Try swapping in a known good maf, and if not that, test the maf circuit itself.

Might also look at the MDP sensor.

I'm guessing your running a GM MAF if you're saying "MAF". Otherwise the stock Karmen-vortex style MAS??? either way get the service info to check the MAF/MAS you're running either with a scope or DMM if you can get access. If your reading a constant at 5mV on you're o2 sensor that means your're stuck slightly rich as the tech at that shop indicated, 450mV would equal a stoichiometric mixture (14.7ish on gasoline) the sensor should be cycling from about 300mV to 850Mv during closed loop steady state operation for emissions/cat purposes).
check fuel pressure when the car is running with any vacuum reference to the regulator disconnected., I think the stock 2G is target 43.5 psi. Also turn the car off and watch the gauge. it should hold pressure for several minutes. if it does not, you could suspect a few things, one being a possible leaking/stuck injector, which would explain your stuck rich condition. you could also ohm out your injectors to get an idea of the condition of the coil.
Do you still have your EGR equipment? A stuck open EGR valve can cause a stuck rich condition because it is recirculating gasses that all the oxygen has been burned already.
If you can find someone with a scope, checking the MAF is easy,
backprobe the mas connector , its a 7 pin connector, PIN 3 is the mas signal. The signal frequency should be 30hz to 50hz at idle depending on idle speed. The frequency should increase smoothly without any glitches or dropouts as RPM is raised. This is a known good Mitsubishi MAS scope pattern for a 97 GSX.

also check the IAT circuit of the MAS as you stated your having cold drivability issues. You could do that on a scantool. just check the temp the sensor is seeing when the engine is cold and compare it to the ambient temperature.
You might as well go right to the PCM if you get a hold of a scope too and check your CKP sensor, CAS sensor, ECT sensor, since you replaced all of that. I've heard its easy to screw up the installation of the CKP sensor. I can send you pics of the scope patterns for all those as well. If you verify proper inputs and outputs to the PCM, that's when it comes time to question the PCM itself. If its got proper inputs/outputs, and power and ground, and everything mechanical is in check, then you got issues

I second @tametalon92, start with the maf:

http://www.dsmtuners.com/threads/maf-or-mas-test-check.279488/#post151385215

Can swap in another MDP sensor to be sure but I would go to the o2 sensor after that since it was not cycling.

tametalon92 said:

Sounds like a bad maf to me. Large throttle inputs causing stumbling or stalling is classic maf failure on alot of cars. You can get rpm by doing just what you did, small throttle inputs. Try swapping in a known good maf, and if not that, test the maf circuit itself.

Might also look at the MDP sensor.

Click to expand...

Thank you, seems like the group consensus is to start with the Mass Airflow Sensor. I'm going to see if I can pick one up from a buddy. Hopefully I can get it done this weekend. I hate knowing the car is inoperable.

let us know how it goes, so many threads end without a follow up on the solution.

Unplug the mass air sensor and try it and see if it changes.

motomattx said:

Unplug the mass air sensor and try it and see if it changes.

Click to expand...

If I unplug it, the idle dips and it feels like its going to die. It idles smooth with it plugged in, but can't accelerate at all. I didn't attempt to drive it with the mass airflow sensor unplugged.

I didn't have any luck sourcing a replacement sensor locally to swap mine with, I'm going to look through the classifieds on here and FB Marketplace and hopefully find a known working one. Even if it doesn't correct the issue, its nice to have spares.

I wanted you to try and drive it with the maf unplugged.

check out the AES Wave Uscope. I used one many times before I had my snap on modis scantool. its a very good hobbyist level lab scope. Think its $180 if you search a little. Scope the MAS dude, don't just load the parts cannon. If the MAS waveform comes back ok at least you'd have a scope to check other stuff then, instead of being stuck with another MAS for no reason.
or unplug it and drive it like he said, but many times unplugging things will cause other drivability issues anyway and put you into a limp mode. It's more of a quick check.
Pinpoint and verify with a scope.

Sorry for the late reply, I got bogged down with the holidays and work. I had an opportunity to swap a known, good MAS and I still have the same issue. I put in new NGK plugs, the others may have been fouled (currently gapped at 0.028). I was thinking about swapping out some better plug wires (the ones on it are a year old, but they were super cheap RockAuto specials).

I did another BLT, there is a faint hissing behind the exhaust manifold heat shield, so I'm leaning towards a boost leak being the culprit. Does anyone know if there is a common leak point behind there (maybe manifold gasket or turbo seals)? I sprayed some PB Blaster on the heatshield bolts, but they are still really on there.

I also noticed the injector furthest to the right when facing the engine smells like fuel and appeared to be slightly wet. I was spraying water for boost leaks so that may explain the wetness, I dried it off so we will see what happens. If I unplug that injector from the harness while running, there is a noticeable change in the idle.

EDIT: No CEL currently

EDIT 2: I am going to check timing to see if I jumped a tooth

I bumped the ignition to attempt to see if the timing was correct. I am assuming this is not the appropriate way because it was too easy, but its about 20 degrees in NJ. I was able to eye-ball it pretty close. You can see the notch on the crank pulley vs the indicator thing. Please feel free to let me know if this rules out timing, or if I need to buck up and do it the appropriate way.

If you think its the timing, it needs to be checked properly. You don't have to keep buying parts and guessing at stuff. IF you think the wires are an issue check the resistance with a DMM, they should not exceed 22,000 ohms. If you can still start it, mist some water on the plug wires while its running and dark out. look for sparks to check for leaks, or a better way would be to have an insulated probe with a wire on it that you can ground to the engine. then drag the probe along the wires and see if there is a leak that way. It probably isn't the wires though.

you can do some quick checks of the coils as well with a DMM. I don't remember what the primary or secondary resistance is off hand, but im sure you can find them in here or with googles help.
I'd also pull the injectors and look at the nozzle. I had a stumble and misfires for a while and it ended up being build up on the injectors. ran cleaner through them and cleaned off the nozzles themselves and drove great after that.
You may want to retrace your steps in a lot of the parts you replaced also. do you know what your long and short term fuel trims are right now?

- Locate the source of that hissing sound.
- Visually inspect injector nozzles and use a DMM to measure resistance/check for opens & shorts.
- use a scan tool or PC to check data to the PCM (IAT sensor, ECT sensor)
- Check engine timing
- pull the fuel filter and see if you can blow through it easily.
- do a dynamic check of the fuel pressure if you can, see if it drops when you accelerate or raise RPM, if it does think about checking the fuel filter or fuel pump pre-filter.

Alright, I've had the chance to properly check timing, which is fine. My buddy helped me with some diagnostic also. The EGR valve was completely covered in crud and maybe stuck open. I installed another one and that resolved the majority of my issue. I can drive the car, even on the highway if I stay out of boost. Its still running lean, and if I floor it, it will fall flat on its face. I did another boost leak, it came back with no issues.

Also, while troubleshooting, I hand cleaned the injectors but I think the fuel rail is too dirty to salvage. I bought a used set of injectors (flow tested), fuel rail and fuel pressure regulator from a forum member. I'm thinking that will resolve the remainder of the issues. I think this is logical as the car sat in a garage untouched for 10 years. I've flushed the fluids and changed the fuel filter already, but the injectors, rail and fuel pressure regulator were never touched. Once received and installed, I will add a follow up.