My 2.0 D-jet has problem : Idles smoothly at start up and cold. As it warms up, it "spits" and cuts out and gets progressively worse the warmer it gets. Is this a CHTS problem maybe? I will test the ohms today and repost.

I thought this would be an ignition system fault such as a bad rotor / distributor or plug wire, but I noticed it gets twice as bad when I put the air box on.

I can only increase the idle at the throttle body and not decrease and I believe the ECU knob is at the center (there's a mark on mine?) :

1) what would the default setting for ECU knob be and how to find it;
2) what is likely causing the "spitting"

I don't see any vacuum leaks at all , and all my injectors are brand new, timing seems right as rain, and dwell and points are spot on, and my air temperature sensor is showing 195ohms, my CHTS is new. The AAR valve is working.

Starts smoothly and idles low around 400 rpm not spitting at all , but after about 20-30 seconds idle jumps to 1100 rpm and starts "spitting" and so checked AARV it is closed

Thanks in advance

I experienced similar issues with dirty trigger points.

Default setting for the ECU knob somewhere near the center. Does the condition change when you turn the knob in either direction? (CW= richen mixture, CCW = leaner)

Are you getting enough fuel to the injectors? (bad pump, clogged filter, etc.)
Vacuum hoses hooked up correctly?
Vacuum leak will cause a high idle, but shouldn't cause the engine to run rough, unless the MPS doesn't hold vacuum.

new MPS
no vacuum leaks, all new hoses, all hooked up this isn't the problem
the ECU seems to have no impact
All that stuff in the fuel system is brand new and the pressure on the fuel regulator is correct

I did note that the car starts idles very smoothly but seems a little low, then after about thirty seconds idle jumps to 1100 and it starts spitting.

thanks I can take those out and look at them although I completely rebuilt the dizzy and cleaned those, unless maybe I got some lube on them at some point

New MPS?
If the issue started immediately after installing the MPS, have you vacuum tested it and calibrated it for your engine?

If the ECU knob doesn't have any affect then you are way too lean or too way rich. If it was rich enough to make the ECU knob useless, then you'd probably be flooding your engine and you'd smell gas, so I'm guessing you're way lean, in which case I'd suspect the MPS.

I put the car from dual carbs back to Fuel injection and never have touched the brand new MPS. The idle was super high and turned out the dizzy shaft was frozen, and the AAR was stuck open. After fixing both those issues that’s the first time I noticed the “spitting”

So, in short answer I have never touched the MPS at all and never calibrated it or done anything to it because it’s straight out of the box

How do I check it and “calibrate” it?

You have to open it up to calibrate it, but I wouldn't recommend it until you know for sure all of your other parts are in good working order and you have a way to read the AFR.

For now, see if it holds vacuum. Put a vacuum gauge on it and pull 20 in. Hg. of vacuum, It shouldn't drop below 15 in. Hg in 5 minutes.
All info you need is here: 914 D-Jetronic Parts and Troubleshooting

I can do that but why couldn’t Injust send it back to the rebuilder and tell them to send me one that is properly calibrated?

Bad capacitor can cause some funky stuff...

Unless they also have your car, they won't be able to get the AFR right.
Don't worry about that now. First get a vacuum gauge and see if it leaks.

which capacitor and where

Click to view attachment

That capacitor was just replaced brand new two days ago. Thank you

this was solved: slight leak in vac advance side of DVDA, and slight leak under throttle body because either the plenum was warped or throttle body, fixed with black gasket glue. Also, disconnected air temperature sensor and seems to run better as well

I did not touch the MPS

Unplugging the air temp sensor will richen the AFR mixture.
If it’s running better with the air temp sensor disconnected then it’s likely because your MPS is calibrated such that the AFR is too lean.