I recently purchased an 05 evo 8 and it has developed a very weird problem. It idles perfectly and will cruise at highway speeds perfectly for the most part. But under acceleration it will cut out really bad but, this is where things get weird to me, only sometimes. It will be running perfect then i will shift, it will cut out, then if i let off the throttle and get back on (usually have to do this 2-4 times) it will run all the way through that gear just fine. Then it may run through the next gear perfect but cut out on the next. If i can get it to have full power, it will have full power until i let off the gas completely/shift. Even more weird is this has happened in 2 spirts. It ran like crap for about 2 days then ran perfect for 2 or 3 then has ran like **** for the past day again. I only have a boost gauge at the moment but gauges are on the list of things to get. My bov wasnt working when i bought the car apparently so i just replaced that (its a gfb vented to atmosphere currently bc the one in it was an atmospheric and i have to get some tubing to run it recirc.) I have also replaced the O2 sensor and that didnt help anything. My next step is going to be a walbro 255 unless you guys say something different. I have been thinking fuel pump but my buddy has been thinking otherwise bc of the intermittent part. The only code i have thrown, and only one time, is a p0300. Any help will be greatly appreciated!

 

I would try new spark plugs I chanced this problem down on mine. I checked for boost leaks,compression test and it was as simple as the plugs. Hope this helps. Make sure to gap them to spec.

 

I forgot to mention i did install new plugs. Now it wont idle either. I ordered a fuel pump and i will try that, if that's not it then i will keep searching. I really need to get some gauges to know what its really doing.

 

Start out with a boost leak test, but I would also suggest testing your sensors before you go throwing parts and money at the car. Cam sensors, crank sensor, IACV, TPS, MAP/MAF sensors are all worth looking into. An oscilloscope is great for the cam and crank sensors then the others you should be able to check with a multimeter.

 

If your on a mass air flow the bloe off valve needs to be recirced. That could be your issue. Its like having a big unmetered air leak

 

Used to happen to me all the time, what are you gapping your plugs at? What plugs?

Also, my stock BOV was a part of the problem and would always cause my car to sputter / choke while accelerating, I replaced it at the time with a "crushed" one instead and never had a problem again.

 

Alright first i want to say i appreciate all the help. I finally figured it out and it was something simple of course. First i tried putting my bov back to recirc but that gave me a high idle and seems to have a little run on when i let off the gas so im assuming whatever tune is on there does not want it to recirculate anymore. Next i noticed pieces of my air filter missing. It was a foam style hks filter so i started wondering if that may be collecting on my maf sensor. Sure as **** my maf was all gummed up with some oil/filter pieces so i bought maf cleaner and cleaned it really well and bought a cheap cone filter and my problem is gone. I have the fuel pump coming already so ill probably put that in anyways sense that's one of the next steps for me to make more power. From reading on here, i should be alright with putting that in and not getting a tune for awhile right??

 

Yea a 255 should be drop in.