My evo IX has been having some acceleration issues at higher rpms (4k+) mostly between 4th and 6th under acceleration. It was happening pretty infrequently at first, and it felt like my motor would randomly sag in power when giving it gas. These sags would last for less than half a second and usually seemed to happen when the engine was a bit cold.

Over the past month, I started noticing a more pronounced power sag under the same conditions, but tonight it got pretty bad. My turbo would spin normally, but the acceleration my motor was producing felt extremely sluggish and sloppy (4th-6th). I also noticed tonight that if I kept the gas down during these (now longer) power sags a rattling sound would start somewhere near the rear of car. The frequency is no where near the rpms of my motor, though. Regardless, it kinda freaked me out a bit because I've had extremely little experience what what a knocking motor sounds and/or behaves like.

A few months ago my evo threw a p300 (multiple cylinder misfire). After looking around online a bit, I may have naively dismissed the code. Yesterday it threw three times, so I've been paying way more attention to how my car has been behaving. I'm taking it super easy on the acceleration at this point, but should I keep my evo parked until I can get it looked at?

Some other tidbits of information... The engine sags only happen when the car is actually under load. The motor revs as expected when in neutral. I got my car with a modified exhaust already installed. About a month after I got the car it starting throwing p420s, and I've just been resetting those until I can afford to resolve the issue. Also, my car seems to idle pretty roughly... are evos camed aggressively? It may been in my head but tonight my it seemed to idle worse than normal.

Anyway, would love to get an idea of what could possibly be wrong if any of you have guesses Thanks!

 

Someone suggested spark plugs. I am at ~56k miles on this evo, so I'll take a look at em in the morning.

 

Doesnt say type of evo (e.g. 8 or 9) or give any information about the vehicle... so i can only suggest new spark plugs and go with recommended gap (for specified boost).

 

Says ix in the first sentence. P0300 needs to be disabled in the rom, no biggie. P0420, if you have a stock exhaust then your cat needs replaced, if on test pipe you need the 02 sim patch added to your rom. The power sag could be caused by a clogged cat if you have one.

 

When is sags, does it suddenly pick back up like a bat out of hell? if so...it might just be your clutch slipping.

 

warm up your car... take it for like a 5 mile drive, come home and pop the hood and take off the oil cap... Is there light smoke coming out right after you drive it?

 

What would that mean?

 

Does the car have a full turbo back? High flow cat? test pipe? I'd do as the guy above suggested and get some new plugs put in at the correct gap. Also, if you have a cat, it may be clogged. Does it smell like rotten eggs at all?

 

You said 6 speed so Im guessing its a IX MR... so check plugs. Its super critical to get the right plugs. NGK IRIDIUMs, not BRK6es or whatever that people run on the VIIIs. Gap them around .022
Does it feel like fuel cut? Could be knock sensor pulling timing?