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I always start by blocking the EGR. It often sticks open and the idle gets rough or even dies. Other than that the car will run fine.

I usually cut up a soda can to temporarily block the EGR off.

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The idle on my (departed) gen II got rough and slow. It was a gunked up idle circuit in the TB... apparently a common problem fixed by the dealer with some carb clean. My gen I (still running) never had that problem.

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has it idled rough since the timing belt change? it may be off a tooth.

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I had the same thought, but from what I have read, one tooth off is enough to throw a code. It still has good "power" (by Neon's standard), starts quickly without a fuss, etc.

It had a little shake before, but the motor mounts were shot, so I probably wasn't feeling it....

I can live with it.....it's just one of those little things I wish I had the answer to...

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Did other Chrysler engines have fuel rails that would internally rust, maybe early 3.9/5.2/5.9 Magnum v8s?

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Did they ever idle dead smooth?

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Did they ever idle dead smooth?

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Did you compare the old mounts vs. the new? I ran into the same situation with my Daytona. Side mount was completely torn, engine mount ripped and trans. mount twisted badly. Replaced them all.

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Yea, was going to mention that but was focused on the vibration. I have to clean my IAC about once a year. I usually just doing it when I clean my K&N since I am in there anyway. I know the autos are a little rougher and could be the tranny mount or even the torque converter causing. Just as a follow up, if you are using a lot more fuel then it is probably learning. I dropped about 5mpg, it was like running e-85 mileage.

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One of the things we ran into at the dealer was rust from inside the fuel rail crapping up the injectors causing a rough idle.

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Usually we would replace the rail, if it was under warranty we would just replace all of it since Mopar was paying the bill.

Once the rail starts going it isn't going to stop.

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Hmm....sounds expensive since I don't have a warranty.

Today I will try cleaning the IAC first and cleaning the throttle body with TB friendly cleaner.

The next step after that I will take the rail off and start poking around there to see what I find. I will post pics if anything looks weird.

Could you actually see rust particles in the injector? Or were they just to small and wedged down there?

Any other thoughts of where I could try looking?

Thanks again! It would be sweet if I had the only complete answer on the internet how to fix this problem. It is a challenge now!

eightlitermopar

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Just spray everything including the TB side. I have connected power to actuate the valve but it doesn't seem needed if it seems to be working, just spray both sides. Not sure on that cap. It could be a problem but I would think it would be more noticeable of a stumble if it had a vacuum leak.

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Could you actually see rust particles in the injector? Or were they just to small and wedged down there?

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You might check to see if you have plenty of clearance between the core support and the engine and trans. I have seen alot of neons that have bottomed out at some time or another and pushed the core support back into the engine of trans. Especially the second gen cars. The The PCM and rad fans like to come in contact with the trans causing the issue you describe. One other thing, Have you ever done a compression test on your engine? Later 2.0s had horrible valve jobs and are common for the valves not to seat well and cause miss or shake without setting a MIL.

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I have not checked the compression yet, mostly because I am afraid I am going to find a low cylinder. I have heard that about these cars as well. Also, the car drives great (other than the idle, which isn't horrible) and it gets great mileage, so even if I have a dead cylinder....I probably wouldn't do anything about it anyway

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In my experience, when the IAC is dirty the idle is slow to respond or unresponsive. As in idles too high or the engine dies at idle because it is too low. The IAC is just a tapered plunger that plugs and unplugs a by-pass hole in the throttle body that allows more or less air into the engine.

It doesn't usually cause a rough running idle condition, unless it causes an extremely low idle that causes the engine to shake.

I usually spray carb cleaner in it and let it soak for awhile and then spray it again. Be sure to remove the gasket/seal first.

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I did the timing belt, crank seal, and cam seal and was very careful on getting the timing marks correct. The car ran perfect for a few thousand miles and then the misfire codes came up.

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I have heard over the years the only thing a Dodge likes is Champions. I found that out too with 360 Magnum: tried NGK's and wound up going back to Champions.

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...........I'll have to check my coil pack too, and I still have to check the resistance on my injectors.

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I had 12.4 to 12.7 Ohm all the way across on mine.

Injector Testing

Also, in that troubleshooting series I used their method for testing the coil:

Coil Test

Had a nice, fat spark.

I pulled all the plugs last night and tightened the gap to .30: run it again for awhile and see what happens.

Good luck.

I'm still thinking about drilling the hole in the throttle plate....

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...........I'll have to check my coil pack too, and I still have to check the resistance on my injectors.

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I had 12.4 to 12.7 Ohm all the way across on mine.

Injector Testing

Also, in that troubleshooting series I used their method for testing the coil:

Coil Test

Had a nice, fat spark.

I pulled all the plugs last night and tightened the gap to .30: run it again for awhile and see what happens.

Good luck.

I'm still thinking about drilling the hole in the throttle plate....

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I have an 04 Neon with 95,000. miles
I am the original owner. This car had a rough idle since day 1. Dealer told me it's normal.
Recently it has a bad stumble, almost like it cuts out. In the past I have put 2 MSD coils on it and changed plugs and wires. Recently replaced
the solenoid on the fire wall for emissions but that didn't help.

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Have the timing belt rechecked. It is off a tooth on the can sprockets

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I thought of this, but I understand that if it is off 1 tooth it will throw a code

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You might try directing some propane from an unlit torch into the intake to the air filter after the engine is fully warmed up.
(when started cold the air fuel ratio is very rich anyway)

If one or more of your fuel injector tips have deposit build ups interfering with the short solenoid plunger up down at idle, the extra propane should smooth out the idle.

If the IAC is working correctly it should adjust while this is happening and RPM should keep returning to spec as the propane is quickly added or taken away.

While you have the propane torch out check for air leaking past gaskets or o- rings.r

Carbon deposits on the backsides of intake valves can also cause a rough idle.

If you are going to keep driving it
add a bottle of Chevron Techron Plus to your next tank,
a bottle of Gumout Regane to the 2nd tank,
then a bottle of Redline SI-1 to the third tank.

This is about the cheapest thing you can do
considering the cost of man-hrs
and based on the idea that:
"what one cleaner cannot dissolve, another one might".

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