I noticed a problem when driving the car for long periods of time. The problem that I have is after driving for more than 20 miles consistently on the highway, the car starts to accelerate sluggish. I also noticed that if Im cruising at 40 and go wot and just back off throttle to 85-90%, the car accelerates faster. I've been dealing with this issue for about a year now. I've change wires, coils, injectors, spark plugs, did boost leak tests, changed o2 sensor, pvc valve, and egr ( need to just take that off eventually) compression test 165 across the board. My mpg varies 190 to 250 with regular driving. I'm lost. No check engine lights. It does idle lumpy at times. Acceleration over 100mph takes forever.

 

are you tuned on speed density? Have an omni 4 bar map sensor?

 

Are you on stock exhaust? If yes I'd say your cat .

 

This Evo is stock. Cat was dug out recently thinking it was that cat and was going full exuast at some point. The problem was happening before that. And it's still happening. Before I tune I want it to run good stock. This car has 128k miles.

 

Throttle body seals? Sometimes they only leak at part throttle. Do you have a wideband? Might be fuel related too.

 

Are you tuned and dont know it? It could be your just dumping fuel.
Are you the original owner?

 

I've changed the seals already. wb is in the works.

 

I'm not the original owner, I wish I didn't sell my evo back in 2008. But I know its stock. I changed the valve cover seal about a year ago and after 128k miles, it still looks brand new. I have a tactrix cable from my previous car and did look into the tune and it looked stock. But the car was fine at one point of me purchasing it. Is it possible to have the spring on the throttle body to not wound tight enough after the shaft seal install? In evo's scan it reads 100% at wot.

 

are you getting 160-180 miles per tank?

 

It varies 190-250 with regular driving.

 

Over 10 years of owning an EVO and i never reached 190 miles per tank.
250 would be impossible! Unless i had a 42r!!
Regular EVO driving i never went over 180.
it might mean your EVO's tuned very lean???

 

I hit 320 a handful of times many years ago while on stock turbo between 2006-2010, been running e85 after that and now a larger turbo.

 

Sounds to me like you have knock issues retarding timing or your running very rich for some reason--

 

You were running extra lean!!
Everyone kniws EVO's run oink rich from factory.

 

No, I wasn't running lean. I didn't modify the fueling until 2010 when I really began to change the fuel pump and injectors. Heck, the car was still on factory exhaust all the way up to end of 2010. I've owned this car for 10 years now and am the original owner.

The oink rich you speak of is only during full throttle, not when cruising around out of boost.