Evo 4 Idle Issue, Misfire/Sputter, and Hesitation
 

So as title states, been dealing with these issues for a bit now and have been trying to narrow it down for a while and before i throw any more parts at it, id like to get some opinions and maybe some insight from someone that has experienced similar issues.

The car is a 1997 Lancer Evo IV GSR and is nearly stock. Only mods are turbo back exhaust, boost gauge, and turbo timer.


Problems all started with one day going out to the car and starting it and could hear a slight misfire when idling cold until it got up to temperature and then it was fine and no issues driving once warm. Even if i drove it a little cold it wouldn't really be noticeable and just misfire slightly. Its progressively got worse since then though. Now the misfire is much more noticeable and if i try to drive it cold the car will misfire and sputter like crazy and hesitate until about 3-4 grand and then it will rev fine passed that but the car is barely driveable until its up to operating temperature. Once up to operating temperature though, the car will run a lot better but still has a slight misfire and at idle and a little hesitation when revving before 3-4 grand and then pulls great in rpms passed that.

Unfortunately its not suffisticated enough to throw any codes as ive checked and no engine light.

Since, i've replaced spark plugs with BPR7ES gapped to 6.5mm, cleaned off MAF sensor, cleaned throttle body, replaced coolant temp sender, boost leak test ( No leaks ), and replaced fuel filter.

Been thinking of replacing coil packs, leads, and replacing spark plugs with the original OEM spark plugs from JAPAN. Was thinking that the IACV could be giving me issues as well but wouldn't it be hard starting warm as well? cause it starts great when its warm. I did try disconnecting the IACV when idling cold and while its misfiring and no change happened but it doesn;t make sense to me that it would misfire because of the IACV when its not idling but hoping someone will prove me wrong. Other parts im thinking of replacing is the MAF sensor as well as i heard they can be pretty tempermental.

But anyway, if anybody could give me a few pointer or shed some insight on my problem thatd be great and much appreciated! I've ran out of idea and things to check and am at the point of just throwing parts at it until its fixed so before i spend a bunch of money doing so i figured id ask.

Thanks

first make sure you have a good fuel. then tighten the gap. You meant .65mm right? make it .5mm or .02 inch. if that doesn't fix it i'd change the coils and wires. I would also suggest getting a wideband to make sure you are getting the correct amount of fuel.

Re-gap the plug (to about 0.020") and try again as the guy above said. :}

Oops, yes of course i meant .65mm lol, my bad. But alright i will try tightening the gap then go from there and order coils and wires if no change. And yes ive gone through a couple tanks of fuel from a few different places and no change. Even ran some fuel injector cleaner and what not through it.

And wideband would be great but im not looking at keeping this evo for long term. I just imported it this year and have been just tinkering with it and enjoying it until school is done and then probably selling and getting an evo 6 or something.

Thanks for the tips though. Ill keep you updated.

Hope you get the Evo IV fixed. That is personally my favorite Evo. I am planning on converting my mirage into an Evo IV one day.

How many miles are on your stocker Evo? The reason I ask is I'm wondering if the stock fuel injectors are operating correctly. If they are partially clogged, they could possibly put out a weak stream instead of a mist and would definitely cause rough running when cold. When the engine warms up, it more easily atomizes the fuel, causing the better running. Also, revving the engine moves the incoming air faster, aiding the atomization. It may not be the issue, but if your plug repair isn't getting it, you could try some fuel injector cleaner (preferably the kind that gets run INSTEAD of fuel that you might get done at a repair shop) and see how it goes, or maybe the stock injectors are the same as more current models. I'm sure there are quite a few stock injectors for Evo 8 and 9 that you get cheaply here on the forum. Good luck to you!

Hey, get fixsed your car ? what was the problem ? i have same issue with evo 4

Try closing down the gap. I never run more than .028