QuestionIn an attempt to try to sort out the continual rough (or variable) idle (while engaged in gear, but not while in park or neutral) on a dear freind's 2002 Dodge Neon with the 2.0 liter engine and automatic transmission, I initially suggested several "clean up" potentials, as I came in contact with the car with approximately 40,000 miles on it...
Change oil (5/30 - SJ grade) several times over 2,000 miles with 1 qt Rislone and/or 1 pint of Marvel Mystery oil to clean all internals, as well, run quality brand gas with recommended injector and upper cylinder cleaner, such as about three cans of BG 444. Between these two non invasive "remedy's", things might get better.
So far, no measurable improvement... The air filter is super clean, by the way.
So, at this point, possibly changing spark plugs might be in order... I cannot say.
Given some of the aforementioned information I've offered, perhpas with your insight, experience and expertise you might be able to shed additional light on this continuing rough idle situation.
I've read where a host of other things such as O2 sensor, valve springs or timing belt might contribute. All I can say is that either at idle in neutral/park, or, once under way such as the open road the engine appears to be "just fine".
Your response would be an honor to receive.
Thank you.
AnswerHello John,
Thank you for the kind and generous accolade, and the detailed question. I believe that the 2002 Neon (and probably other Neons as well) does not have an option available to query the engine controller as to whether it has observed any faults in the system that might help diagnose the problem. So that means one either buys a code reader or pays a shop to read out the stored codes. Up through the mid to late '90s (and even in other model lines there still is) the codes could be accessed via the ignition switch. So we are left with the options of the pre-computer age.
I would certainly ask the owner how long it has been since the spark plugs were changed. In my experience when they reach the 25,000 mile point you certainly can experience miss and variable idle due to wear out of the plugs. Another possibility is that a vacuum leak, a PCV valve that is cruddy, or a slightly ajar exhaust gas recirculation valve is leaning out the mixture at idle. I would do the plugs if warranted and look around for those other possibilities. If that didn't prove helpful, then either buying a code reader (around $50-100) for the Neon or paying for a readout would be the next step. If you do have to get the codes, let me know the result. I have a '98 shop manual for that 2.0L engine and it has an approach given for each of the fault codes. You can learn about code readout at:
www.allpar.com/fix/codes.html
and they also have a list of the codes.
Roland
