Sorry for the long post, just trying to be as descriptive as possible...

I have a 2000 Plymouth Neon that is stuttering when getting up to speed (about every 10 mph increase it stutters for a little bit before the engine kicks back in). During this stuttering the rpm's don't seem to increase (no rpm gauge, just going by engine noise). Also if I go above 50 mph for more than 10 or so miles it starts stuttering/losing power, in the same manner as getting up to speed, until it eventually dies.

Sometimes I can pull off to the side of the road and it will stay running. If it stays running I can usually start going again after 5-10 minutes, but it doesn't last long before acting up again. If it dies I have to wait anywhere from 10 minutes to 2.5 hours before I can start it up again and drive for another few miles. The longer I wait, the longer it will drive without breaking down again.

The first things we replaced were the spark plugs, wires, and valve cover gasket as there was a little oil in one of the plugs, also got an oil change. Then it was still acting up, so we took it to another mechanic and they replaced the water pump, timing belt, ignition coil, fuel injector #4, cam seal, front crank seal, and a fuel service (oil and fuel tank additives, and an engine induction service).

After getting it back it was still acting up, so we replaced the MAP sensor. We also put in octane booster and a full tank of gas. After this it ran fine for a few days, but it has since been acting up again.

The check engine light only flashes when stuttering, there have been a few occasions where it has stayed on. I just did a code diagnostic on it by turning the key to the on position, then back off 3 times, and the only code it pulled was P1684: Battery Was Disconnected.
Any help will be greatly appreciated, if you need more info I will do my best to get you what you need.

 

I would do a compression test.

 

Yeah I agree with doing a compression test. You may have a bad head gasket or something of the likes.

 

I forgot to mention the second shop I took it to (the one that replaced the water pump, ignition coil, etc) ran a compression test on all cylinders after finding code P0304 (cylinder 4 misfire) and found the compression to be ok. For the code they found spark plug #4 was fouled and injector #4 stuck open (hence why they replaced it). I was driving it today and the check engine light came on long enough for me to get a new code (P0171: 1/1 Fuel System Lean).

 

Lean either means 1 of 2 things. Not enough fuel or too much air. Could be a lot of stuff.

 

Might start by replacing O2 sensors.

 

Did you ever find out what the problem is. My 2005 neon does the same thing.

 

too much air check for a crack in the intake rubber boot that looks like a shock cover, sometimes it can have a crak and cause this.

 

My car does this exact same thing . Did you ever figure out tge exact problem