2004 Neon SXT - Rough idle when in drive

Solo2GS · Post by **Solo2GS** » Mon Oct 25, 2010 8:54 pm

I have a problem that the shop can't seem to resolve. The car has run great up to this point with all the standard maintenance done (oil changes, transmission fluid changes, timing belt... over its lifetime). Changed out plugs & wires with no affect.

Recently the car developed a very rough idle / rattle while in gear. Once the RPM rises slightly while going down the road it is gone. The shop replaced all 3 engine mounts. The center one was broken and the 2 torque struts extremely worn out. Yet the problem still exists... They have adjusted them several times with no luck in improving the vibration. The car was put on a Vac system to test air flow and such with no problems found...

No resolution has been found for the vibration yet. The longer you sit the more obnoxious it seems to get and you feel it in the steering wheel rather well! Idle speed appears normal. Drives down the road and shifts just fine. Can rev the engine in park with no vibration...

Suggestions? Thanks for any help...

2004 Dodge Neon SXT 2.0L
Automatic | 110K

Post by **occasional demons** » Mon Oct 25, 2010 9:07 pm

Do you know if they cleaned the IAC valve?

Solo2GS · Post by **Solo2GS** » Mon Oct 25, 2010 9:35 pm

I'll have to ask tomorrow.

What would the cleaning process be? Where is it located at?

Post by **occasional demons** » Mon Oct 25, 2010 10:12 pm

viewtopic.php?t=52803

It just needs removed, and soaked in Seafoam overnight, or sprayed with Carb cleaner.

If soaking it, just prop it so the holes are up, and fill them, vs dunking the whole thing.

Solo2GS · Post by **Solo2GS** » Tue Oct 26, 2010 10:53 pm

I sprayed out and let soak for 4 hours the housing. It wasn't very dirty. Had no affect.

I cannot seem to find what the spec is for idle RPMs. In Park it idles at 730 RPM (+-10) and when in Drive it bumps up to 775 RPM (+-10) on my Sun multimeter.

Add about 100 RPM and the vibration you feel in the steering wheel goes away! Anyone know what it is supposed to idle at?

Post by **occasional demons** » Wed Oct 27, 2010 7:24 am

800ish. You could try drilling a small hole in the throttle plate, but depending on how close the IAC is to seating at the current RPM, will depend on whether that is effective or not. It it can still hit it's target rpm, it will. You could plug the IAC hole with your finger to check to see if it is even working. Idle should drop, then raise when your finger is removed, and settle back to where it was.

esteinmaier · Post by **esteinmaier** » Wed Oct 27, 2010 12:05 pm

Sounds more to me like you need spark plugs.

Solo2GS · Post by **Solo2GS** » Fri Oct 29, 2010 11:27 am

Changed out the plugs and wires. Cleaned/soaked the IAC. Cleaned the MAP sensor in the intake manifold. Ran a big container of Tecron cleaner through a tank of gas this week. No changes...

Going to get an auto part store to check if there are any codes.

esteinmaier · Post by **esteinmaier** » Fri Oct 29, 2010 11:34 am

Exhaust leak or o2 sensor?

Post by **occasional demons** » Fri Oct 29, 2010 12:31 pm

Solo2GS wrote:
Going to get an auto part store to check if there are any codes.

Just shut the engine off, then turn the key on three times. Codes, if any, will display on the odometer. If you have anything besides 1684, or "done" then we can work from there.

Exhaust leak or o2 sensor?

Eric brings up a god point.
Any cracks in the exhaust manifold will do all kinds of weird stuff, since the o2 sensor is seeing more oxygen in the exhaust. The pcm will try in vain to correct it.

Solo2GS · Post by **Solo2GS** » Mon Nov 01, 2010 12:07 am

No exhaust leaks that I can hear cold or warm.

I did check the codes and it lists one.

P0627 - Open or shorted condition detected in fuel pump relay control circuit.

Drove it almost 200 miles today. Seem to cruise down the highway great. Only the rough idle issue. You come to a stop and the idle seems fine at first then in a few seconds it drops slightly and that is where you get a vibration. Obviously from a low idle... Idle video

chessmasterscds · Post by **chessmasterscds** » Sat Feb 18, 2012 5:35 pm

Hi, I was wondering if you have found your neon's problem 'cause I have been experiencing this very same problem for over 3 years now and no shop have been able to figure it out. I've done everything you said you did.... And the rough idle persists... I'm kind of used to it now but I still want to fix it..., mine is an 04 dodge neon SXT just like yours by the way.

Public Disturbance · Post by **Public Disturbance** » Sat Feb 18, 2012 7:39 pm

Completely off topic but I had no clue about the code thing that is so cool I just went and did it and im assuming that if it just say "done" and goes to -----------that means no codes

Post by **occasional demons** » Sat Feb 18, 2012 7:40 pm

I doubt they will respond...

Last Visited: Sun Oct 31, 2010 9:07 pm

Post by **occasional demons** » Sat Feb 18, 2012 7:42 pm

Public Disturbance wrote:l I just went and did it and im assuming that if it just say "done" and goes to -----------that means no codes

It means your neon is done. Take it out of the oven already!

But yeah there is nothing to report, move along!

gcretro · Post by **gcretro** » Fri Mar 16, 2012 11:32 pm

I have a bit of low/erratic idle when in gear.

Look at this software update. dealer said about $85 to do it. I said to hell with it... since my idle issue is not bad and I was able to adjust idle with the screw on the TB

http://www.ertyu.org/steven_nikkel/neon ... 025-04.pdf

00neonlv · Post by **00neonlv** » Thu Mar 29, 2012 4:48 pm

Hey guys my 00 neon is the same way i did new mounts and spark plug and new head when i did headgasket but idles bad and now it spudders like when i hit the gas some times it will hesitate to move????
and a code saying running too lean bank 1