ej swap idle issues

[turbosubarubrat]

My 86 obd1 ej22 swapped hatchback ran great all summer then towards the end of September it started to run on 3 cylinders at idle with codes 24(iac) and 33(vss). It's a 90 ej22 with all the electric components from the legacy i parted out including the C8 flasher bulb ecm, harness, ect. At first i tried to swap the iac out with a know good one after cleaning it really good. Same problem. Swapped out the ecm with one from a 91 that doesn't have a flasher bulb and both codes when away. Ran fine besides it would randomly run rough and get a check engine light(wired to ecs light) when slowing down so you would have to stop let the idle almost kill it then it would go back up to about 750. So i wired up the vss and my current problem i have right now is  that after the engine is warmed up for a little bit it starts to idle up and down from almost dieing to idle with no codes. I don't have the neutral switch wired up and i've heard about people adding a clutch switch. Would any of theses help or does any have any ideas. If i plug the 90 ecm back in it still has the code 24(iac).