(Car is a '05 Neon SXT w/ automatic)
Haven't had any issues with the Neon I got about 500 miles ago. Though in that whole time I've noticed it getting quite awful MPG, about 15 on average the last two times I filled it up and went to empty. Funny thing is, the car runs pretty fine. Doesn't sound like it's running rich at all and performs as it should, yet gas mileage has been the same as a 350cui V8 in the city.

Now, one thing I noticed ever since getting it was on some occasions the idle drops to around 550rpm. Heard it was something to do with updating a part I forget the name of, but supposedly it's harmless. Not 100% sure on that.

Anyone got a good clue of what could be causing this? I can try replacing the plugs and wires when I get a chance, which I've seen can help sometimes.

 

I am curious as well as to what to look for. My neon runs good I am not sure of the the mpg yet but the idle gets rough when stopped and in drive or when I turn on the ac. I have read about drilling an extra hole in the throttle but I don't know it that is the correct answer.

 

I had a problem with the drivers side radiator fan was not coming on, the fan motor was dead. If the a/c is on when coming to a stop it ran bad. Just a thought. So no trouble codes, or some stored in memory.?

 

My experience with neons is they get crap milage for what they are anyway. Dodge decided to tune them "sporty" instead of tuning for efficiency. I have mine and a couple friends have one though they claim 29mpg on the sticker they are more like 20-22 in real life (the way i drive i usually beat the sticker) that is pretty much the same as a V6 F150. If you want to relearn to drive you can do better but i just dont have it in me to run the engine at 2500-3000 rpms at 35mph it just seems wrong but it is where these engines are efficient. If you are down around 15 how does your air filter look? Spark plugs? Plug wires? Vacuum leak?

 

Sounds like it might need a tuneup? I got 23ish around town (I live in the mountains, so plenty of hills) and I'd get about 30-31 on the highway.

 

I still say you need to check your air filter, plug wires, and plugs (use cheap copper plugs neons hate Platinum) first. However I was looking online for why my car wouldn't idle and the IAC valve kept coming up. Many places said that if the IAC or your Mass Air Flow sensor were dirty that they could cause crap milage. A can of Mass Air Flow sensor cleaner (I recently found out that there is actually such a thing) and a quick search on YouTube (many videos) may give you what you need to improve your milage. Oh and a can of Seafoam in the fuel tank couldn't hurt. I have no idea what it actually is but as far as cleaning an engine goes it seems to be a bottle of miracle.
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Almost forgot to reply to this thread, whoops.
Replaced the front tires not too long ago because apparently the tread was coming apart slowly on the driver's side front tire. I checked a week before this happened and it still looked "okay" at most, not as bad as it did then. All the tires needed a balancing, too.

I first noticed when I was heading 70-80mph down the interstate and the car kinda shook and started wobbling a bunch. Grabbed the equally as old spare in the trunk and took it easy on the way home. Could have been a lot worse of a scenario because I was being an idiot and riding around on ancient rubber. Learned my lesson for sure.

The tires were seven years old and cracking so I knew I had to replace them pretty soon after getting the car. The rears are still the old tires because I'm low on money aha, but those will get replaced soon as I can get to it. With the new front tires I've noticed the gas mileage being a fair bit better than before, but where I live is mostly intersections and merging onto the highway, my MPG is roughly 25-ish at best.

 

Doesn't sound like anything a good tune up won't help, but I've noticed Neons aren't as great on gas as you'd think. My average is probably low to mid 20s, while it seems to do pretty good on the highway with the cruise on, I've noticed it's a pig in town with stop and go traffic (my v8 Trailblazer and v6 Bravada both get better mileage in town!).
And running the AC in town is even worse, my compressor went out recently and for now I just bypassed it with a non AC belt and noticed a large improvement, even over having it hooked up but not running.