Put the original hoses back on from the throttle body to the EGR valve, left the replacement one in the back. Another thing I noticed, I can hear a distinct "suck" sound as I hit the throttle right before the engine revs, not sure if that the vacuum sucking for air or just the throttle plate opening and creating the demand for air. I also hear a air "let off" after it shuts down. The guy I talked to at the Autoparts store said he thinks it might be a vacuum leak as well and to him, me as well, it sounds like its coming from the top center of the engine. Not giving up, just getting frustrated, the joy of older cars.
FYI-I already replaced the IAC valve, was extra sure to make sure the o-ring was seated before completing the install.
Throttle position censor?
Actuation valve?
I am just having difficulty finding the issue at this point.
How about old fuel still in the system? Fuel filter? Fuel pump?
Is there a way to check the fuel pressure to make sure its OK?

 

OK, did the smoke machine vacuum leak check. used two different vacuum lines and the intake with no luck. I did not find a leak anywhere. It got worse after I revved the engine a few times afterwards, started stalling out and idling at 200RPM or lower. Going to go to the auto store and try to catch a freeze frame on the scanner. My question is.... what the hell am I looking for?!?!?!
Got another scan, still the same P0300, no relevant data on their scanner. It is stalling out now on a regular basis during driving. Before I go ordering more parts, I am wondering what else I can check. I feel like fuel filter is the next stop, followed by seafoam in the tank and intake. I need to know the methods for checking things like if plugs are firing, am I getting fuel pressure (the right fuel pressure), and I think I need someone to do a professional leak check on the vacuum system (not sure my halloween smoke check was legitimate).

 

The misfired (P0300) could be related to the stalling out you describe. You've got to figure out what caused that. The only real way to do it is to catch live stream data duribg the time stalling out happens. That may show you what causes the stall - fuel starvation, fuel over supply, or something entirely different. Same goes for whether you have proper spark waveform - not something an average tree shade mechanic will have on hand to test properly.
I dont think it's your coils. If one was bad, you'd have specific cylinder misfire, not random ones.

 

I replaced all three coils when Indid the plugs, wires, EGR valve, both upstream O2 sensors, IAC valve, and replaced two vacuum tubes. I also did the spark plug seals and valve cover gaskets because I was there already along with both idler pulleys, tensioner and serpentine belt. I made a lot of headway eliminating faults but this one I am stuck on and pretty sure I need to find a Mitsubishi specialist in the area, dealers aren’t always the best because stuff like this gets charged by the hour PLUS whatever it takes to fix it once they find the culprit.... which of course I would do the work.
anyone know of a depends Mitsubishi mechanic in the Fayetteville, NC area?
Thanks for the reply, this is confirming where I figured I was at

 

I have to ask even if it seems silly, did you thoroughly clean out the throttle body at any point? Doing this greatly increased engine power and brought my idles back up. If you haven't already done it, I suggest a can of brake parts cleaner, a pack of nitrile gloves, and an assortment of abrasives (wire brush, sandpaper, etc). Remove all the electronics from the TB and take apart anything that could have carbon build up inside and clean as best you can.

Another possibility (although unlikely) is the timing belt has stretched a tad over the years or its off half a tooth, not enough to throw a code but enough to affect performance.

EDIT: Before you remove the throttle position sensor, make a mark on both the sensor and throttle body so you know where it's supposed to be when you reinstall! Otherwise the TPS will require calibration with a multimeter.

 

So, I had budgeted around $2000 to make this bad boy work and be more comfortable to drive daily, the following is what I have done to address the engine codes and increase reliability:
plugs
wires
coils
spark plug seals
valve cover seals
Both left and right upstream O2 sensors
IAC vale
EGR valve
sepentine belt
idlers
tensioner
a few new vacuum hoses
new wipers all around
More recently, after all but the P0300 code was eliminated, I had the following done:
fuel pump
fuel filter
shocks
struts
bellows
bushings
After the last round of parts it was determined that cylinders 3/6 were not getting the signal to fire. Searching here led me to order an ICM (along with the expert advice from a wry good local shop, Brakes and Axles in Hope Mills, NC) and after the installation it is running like a top.
All in I am just under $2,000 in parts and labor. It’s runs like a top right now, headed to the DMV to get it registered Monday or Tuesday, very excited to start picking and pulling at the remainder of it, replacing little things here and there to improve reliability and comfort while having a bullet proof daily driver. Thanks to everyone here for thier help and advice. At only 130K miles I expect this hoopdie to be around for a hot minute!

 

You and I both have nearly similar stories , I grabbed an 01 xls that had been sitting and same thing , fist I had the egr code , then misfire cylinder 6 , now multiple misfire , I've replaced the plugs ,wires , VC gaskets with tube seals. Stoll running rough. I'm following for advice because I want mine running good