Alright so I picked up an Evo x I'm the 4th owner it has a conservative tune pushing 330 block is past breaking point. Has bolt on cold pipes and full exhaust. When I picked it up began accelerating in 2nd gear onto freeway. noticed it made back fire or misfire and revs jumped I switched to next and same showed matinance engine light. Has gone on and off in the two weeks I've owned it switched sparks to ngk iridium and chained oil and filter. Did it again and light stays on. Only when I floor it on a 1st gear 20mph it does not do that acs is off. Auto parts obd2 can't read the ecu. Could it be coil packs? I calibrated sparks? Or need of retune it has 78xxxmiles

 

knock? incorrect gapped spark plugs (gapped too big)?

 

Find some way to pull the ecu codes. Another code checker or different parts store.

 

Did it drive ok when you took possession of it or did it start acting up later on?

I don't know the story behind your acquisition but if the previous owner removed any mods from the car without a re-tune, it's probably your issue. If that might be the case I would highly recommend you STOP driving it until you can get a re-tune.

If it started happening after you bought it, proceed with getting the codes pulled and troubleshoot accordingly.