This
https://www.murata-ps.com/en/dms-eb2.html is an accessory to their line of panel meters. I have nothing but high praise for the company. I used on of their models so that mass flow controllers in the semiconductor industry would read in engineering units. I did something cute. I had a switch that placed 5V at the meter and then you adjusted a pot until you read the FS value. Set the decimal point and you were good to go.
Aside: There was one time I had to also calibrate stuff, but there were fixed output voltages of say 5V or 200 mV. I used a secondary number, initially 1.000 to tweek FS.
So, you set the nominal FS and the nominal output and then had tweek number. It was better than 0.956 V/milli-Torr or whatever. Not applicable here.
What would typically do, is divide the not quite 5V (span) to 100 mV (100 mV=100%) for display and set the decimal point accordingly and without loading the source appreciably. 200 mV is usually the "base range".
The TPS is typically ratiometric (my understanding), so you might want to consider that. It's not strictly 5V = 100%. It, whatever the power supply is makes it 100%,
So, if the supply is 5.1V, 100% is 5.1V
To make the meter ratio-metric, you would have to supply a likely buffered and divided new reference from the 5V source you are using.
Many times, the meter requires an isolated supply.
Right now, my head (migraine) isn't capable of figuring out what you actually need.
==
Quick favor. Can you measure the output voltage at 0% throttle and the actual power supply voltage at the TPS and at the ECM?