Sudden decrease in VE and increase in IAC output needed to idle.to idle

I have an evo 8 running on haltech elite 1500. Built bottom end, gsc s3 cams, custom exhaust manifold, 6466, dual wastegates, 2150cc fic injectors, surge tank with deatschwerks 300 and a 420 on flexfuel. Also has ign1a coils. Out of nowhere, it will not idle anymore. Its been idling at 30% iac output and I'm using the zero demand ignition table at about 6° of timing and it loved to idle with those settings. About 2 years ago, I go to start it to leave a parking lot and it would bot run or idle without throttle. Kept the car running with throttle and it came out of it. Didnt happen again until a month ago. Same thing all over again. It did clean itself up though. But now, it won't start without throttle and throttle is needed to keep it running. It goes super rich and the stft will max out trying to pull fuel out of it. I first started with new plugs and flow tested and cleaned the injectors but nothing changed. I then noticed the map sensor would read .6 psi with engine off. I had it running and idling perfectly. Stft's were around 1%. I was looking around trying to get it to act up. After about 15 minutes I bumped the haltech to evo 8 adapter harness and it immediately started to choke and struggle. With engine off, I moved the harness again and the map sensor started jumping around. Okay so I thought an obvious wiring issue. So I cut out the adapter harness and wired the engine harness directly to the ecu. Map sensor reads .1 to -.1 psi with engine off now (it will constantly fluctuate but it's more steady than before). That didn't fix the issue either. I then probed every sensor and checked continuity and voltage. I could not find anything wrong. I then verified cam and crank timing. I switched IAC's but no change. The only way I can get it to idle is pulling 15% fuel out of the whole table and added 40% IAC output. Has anyone ever seen an issue like this? I really doubt its a mechanical issue like timing or a rocker arm that fell off since it doesn't always act up. Im leaning more towards a wiring issue. I apologize for the essay. I tried contacting haltech but they told me contact my tuner (i am the tuner) lol.

My first guess is a fuel pressure regulator issue -- if the regulator is good, is the hose with the reference pressure kinked, pinched or clogged.

Next verify no other mechanical issues -- compression / leakdown good; Cam hasn't skipped timing; trigger still aligned so commanded ignition timing equals delivered timing; send injectors out for cleaning / testing (verify spray pattern is ok on all).

Since you mentioned that it changed behavior when you touched the wiring. I would be looking for a splice issue with sensor power supplies or grounds.

Take advantage of your ECU -- log all the sensors, battery voltage, etc while you wiggle the wiring and try to reproduce the problem. A log showing what changes or doesn't look right can be just the clue you need to fix the root cause. If have an oscilloscope (or know someone that does), that can be helpful for verifying voltage and signals are as expected.

Good Luck!

Not 100 percent sure but it could be about idle stepper motor set wrongly. Considering 2l displacement and very aggressive camshafts the idle RPM should be around 950-1000 RPM I guess for stable idle. Usually 75 percent of that figure should be achieved with idle stepper motor deactivated. So without idle stepper motor the engine should be idleing at 730-750 RPM. If the engine stalls idle target RPM should be raised to 1000-1050 RPM and without idle stepper motor the engine should be idleing at 750-780 RPM without stalling (that is done by turning idle screw bolt in the throttle body). Once the engine isn't stalling the idle stepper motor can be activated and it will provide additional 25 percent of target idle rpm. If Haltech has the same feature of idle stepper motor trim learning like stock system you will need to disconnect battery (when the engine is warm), reconnect it again, start the engine and let it idle for some time without any electrical devices turned on (music, lights, heater fans etc)...

Since you didn't describe otherwise I assume that the problem of decreased VE appears only at idle. If that the case it could be caused by clogged idle stepper motor channel inside of the throttle body.

It is possible you have contamination in the map sensor line contributing to the problem?

Does it still make good power up top? Definitely not a collapsed catylist.