My 2002 Dodge Neon, Automatic transmission is idles rough and drops RPM's when parked or when shifted in reverse and when I come to a stop at a red light, it has poor gas mileage, it hesitates and cuts off when I start it in the mornings(cold). I have had to replace the selenoid, belts,computer, alternator, battery, spark plugs, IAC, TPS, timing belt, water pump, cat. converter, gas cap, radiator, it just had a tune-up and passed smog, all of the O2 sensors have been changed, new motor mounts on it, and now I am getting a code P1684 which states battery has been disconnected in the last 50 starts but it hasn't. Could it be that my camshaft sensor or crankshaft sensor are going bad? The car acts like it wants to cut off while idiling, it is sluggish especially when it hits between 3-4 RPM's. No other codes are pulling up, just the P1684. I have spent so much money on this crappy car and i'm about to drive this car over a cliff but I need it to hang in there another year. Please HELP!

 

Quite a shopping list there...
My first question would be "was the work done in a shop?"

If it was, many procedures start with disconnecting the battery at the negative terminal so unless you have actually started the car and run it 50 times, the code might be valid. Also, the Neons are prone to "idle overshoot" in which the idle drops to a ridiculously low point and you would swear the car is about to stall. Depending on who you talk to, this is part of the programming of the PCM to reduce fuel consumption during idle by lowering the idle when certain criteria are met. I have found that turning the steering wheel about 1/4 turn while idling will induce a power demand and the PCM will return the engine to a more suitable idle.

As I recall with my '01, the camshaft sensor going bad made many of the same symptoms as you describe, but I had some backfiring too.

Was all this work to stop the current symptoms or for other reasons?

 

Thank you for your quick response. The major things that were done was by a mechanic at a shop.Some of the sensors were done by a friend who rebuild cars. The work was done over the last 6 months and I have started the car more than 50 times since the last sensor was put on. I got a couple of new codes today....p0455 and p0442. For some reason my gas cap keeps coming loose. I have a new one on and it still keeps tripping and makes the codes and engine light appear.

 

The first thing I would do is get a locking gas cap. Self loosening caps usually don't just happen. I'm not saying you didn't tighten it, but repeatedly finding it loose and not going as far as you should makes me wonder if someone in the neighborhood has learned how to siphon gas from your tank.

I would start there.

The rough idle is probably idle undershoot. seems to be a trend with the Neon and similar cars with the same engine. Next time it idles rough, try turning the steering wheel 1/4 turn. If the idle speeds up, problem identified.

Joe

 

Well I tried turning the wheel 1/4 of the way and it still idles rough. The p1684 code is still there and that usually goes away when I tighten the gas cap? I'm hoping she starts in the morning. I guess I will be heading back to the shop. Do you know how much it will cost to fix an evap/emissions leak? I have already spent close to $3,000 fixing this car and I'm wondering if I should even bother.

Thank you again......

Chel

 

Are you sure you have the correct gas cap?

I have no idea what an exploratory evap would be. Depends on the shop rate I suppose.

Joe

 

I went on a wild goose chase too when I first got this 2005 neon and it was vibrating a lot. I changed the motor mounts and did a whole lot of other stuff to it. I haven't tried the turning the wheel a quarter of the way but will give it a shot. Now this is what I did to make it tolerable . I loosened the motor mounts a half a turn from the outside of the wheel well not the inside ! This is the only thing that has helped but I was told by many that you need to use the factory mount and adjust the torque struts . The factory mount is water filled and one mechanic told me here that is the reason it vibrates and he did one with a water filled (factory oem) mount and it ran smooth. If I keep this car long enough to do the timing belt I will give it a shot one day but I don't want to do it now because now it's tolerable by turning the motor mount from the outside wheel well out just a bit. Good luck guys.

 

Yeah, I changed the motor mounts twice because they keep cracking due to the vibration. I guess i should have the dealer put the factory ones on. I wonder how much that's going to cost? I'm going to take her in to check for hose leaks and any leaks near the gas can. We will see.....

Thank you for your response. Oh, and turning the wheel actually works or sometimes I put it into neutral and that stops the shaking too.