I just bought a 2003 Mitsubishi Eclipse gs 2.4L and this is my first car and it ran great when I first bought it. Got it cheap though so I was wondering what could be really wrong and why such a good deal... About 2 weeks later after buying it and getting new brake disks, the car turns into poop. The guy doing my breaks plugs a code reading and says "it's pulling up that there's a miss fire". The thing is, I walked into the the place with the car running fine. I didn't have issues till he told me. So I walked out of there thinking he's making it up, there's no way I can have problems with a new car.. but I leave the corner and I step on the gas to the floor to get a good feel and that's when I feel the car stutter and basically feels like the gas is breaks. When I pushed it down the car slowed down and the RPM's was struggling to go up, sounded like it was getting louder but wasn't going anywhere. So I pulled off to the side of the ride and was pissed and called everyone I knew that might have an idea. My first thoughts was that this guy messed my car up because I walked in there with a great car and left with a bad one.. but after that, I made it home. And I let the car sit for a day and the car ran better. The car runs okay when slightly putting your foot on the gas and slowly going faster but if u wanted to put ur foot down on the gas it would stutter a lot and then after a while maybe 3-5 seconds it will start to fully burst into a sports car mode haha. But the stuttering sounds horrible and feels like breaks for a bit. I was starting to get use to this issues and was deciding "okay the car runs okay as long as I slowly go on the gas and not to the floor". But then soon after I start the realize how bad it started to idle and it started to stall on me. And now it has a bad start up. Usually it's 1 miss fail and then I turn the key again and the 2nd time it works fine. But i don't know if that has to do with this. I took the car to my friends and tried cleaning the MAF and it got stuck at my friends house and the car wouldn't start, and if it did if I put gas on the car it would stall, and it would idle hard and give out shortly after. I had to get it towed haha. Sounds like fun. But my dad restarted the computer on the car somehow and the car ran okay after that, but not back to its normal state. Just back to its "slow gas peddle" state. I cleaned the throttle body and the MAF censor and it runs a little better after that incident but still hesitates when going on the gas hard and idles bad when at stop lights. Sometimes stalls but I can feel it going bad so I put it in park and it sounds better, I just put it back in drive as soon as the light is green and im fine. I have yet to clean the IAC valve because it's hard to reach to. But I plan to get there to see if that helps. I also want to mention, the car has a bad fuel neck. When I pump gas, it just leaks out at least 20% of it. I noticed that the neck is pretty rusted too so I plan on getting that replaced but I have no idea if that could lead to any of these issues, maybe having some rust stuck in some tubs. I have no idea. Also want to mention that there is no engine check light on as of the moment.
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Plain and simple, testing needs to be performed. Enough guessing. A misfire is usually related to a lack of spark in one or more cylinders or a fuel injection issue. Or, it could be a base engine issue. Guessing just doesn't cut it though. Seek the guidance of a technician that you can trust that has proper tooling and know-how.
I own the same exact car. Check Engine Light on. Idles bad, turns off sometimes at a red light, hesitates upon acceleration. Went to get an emission test done and the guy would not run the test until I got it fixed. So from there I went to AutoZone to see if I could get the codes. But while there I opened up the hood and immediately saw the problem. The vacuum hose that connects to the main air intake between the MAF Sensor and the throttle body had a broken connector. Someone had actually tried to fix it using silicone. The silicone had dried and plugged up the air flow. I cut the broken piece off with a knife and it plugged in perfectly. Fixed the problem 100%. Didn't cost me a dime. That may or may not be your problem, but just thought I would share my experience.
