Slightly Rough Idle

Hi everyone I got my spark plugs replaced at the local pep boys (1993 Chrysler Lebaron LE 3.0L) a few days ago and my car seems to be running a lot better but the idle is still a bit rought it is most apparent when the car is in park but is barley noticible if at all when the car is in drive while idle. Im not sure why this is, but could I just need a new rotor. Also they said that the automatic tentioner in my car is starting to make noise and should be replaced the guy said that it would cost about 150 dollers could that be why its rough in park but not in drive (probably not) anyway thanks for your opinions.

no, it is not the tensioner, that will only be annoying, and kick your belt off in the rain, and make annoying noises and possibly seize up and chew up your belt, its a good idea to replace it. Your rough idle could be caused from a little carbon build up, or it just needs a tune-up. Also, check your iac motor

did you check for trouble codes? easy w/ the key on-off-on-off-on w/out starting the engine & then you'll see the check engine light flash you some codes...

pepboys shoulda recommend anything else w/ your spark plug change... fuel filter for one

i dunno about the serpentine belt tensioner; it may be a contributing factor... once u select D, the engine's under load. P, means the engine's load will bump up/down along w/ the tensioner's bounce...

I checked the error codes I only get code 55 which if im reading the code sheet right means that its the end of the codes. Im planning on getting the tensioner and belts replaced this weekend so that will take care of that problem. Pep Boys did suggest a fuel system flush with spark plugs I might get that done too when I have the tensioner replaced.

Your rough idle could be caused from a little carbon build up, or it just needs a tune-up. Also, check your iac motor

well, if that's a 3-step process, which includes cleaning some of that carbon build-up from the throttle body area. May or may-not relieve the problem.

I'm guessing on their 3-step process:

add a concentrated fuel system cleaner to your gas tank (u can just buy a chevron/techron based product & do that yourself).

swab the throttle body valve area w/ similar cleaner (easy as well; u can get the throttle body cleaner & DIY).

Inject the cleaner via the fuel rail to clean out the injectors (they usually disconnect the fuel system & use a pressurized can to pump the cleaner/fuel mixture thru).
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To add, using Seafoam-type cleaner to decarbonize the combustion chamber-- may or may not help w/ that minute problem as well. GM top engine cleaner is also widely used as an alternative from what i've seen around the message boards.

I don't think pepboys does that service, because it's a hit-or-miss. Sometimes the plugs/o2 sensor would be covered to the point that they need replacement after the treatment. I mostly heard good stuff w/ doing that but dunno about older,hi-mileage engines...

U think that it also needs a rotor? hmm, they would have recommended it as part of their "tune up" since the technician shoulda inspected that/ cap/ wires/ vaccuum lines/ etc.
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I say do the serpentine belt/tensioner 1st cause that'll be a priority over the minor idling issue. U don't want that belt to be too loose & fly off as EnergyForce suggested.

Well I took my car into the local pep boys and I am glad I did turned out the tensioner was litterally falling apart and had to be replaced. Also had both my belts and the pully replaced (bad tensioner caused really odd wear on the pully). The mechanic there said I got it in just in time before the belt would have either A. Snapped or B. Fallen off the car O_o

Yay! u r lucky to have gotten it done... pepboys, like any other national retailer, are YMMV depending on the people who works @ each store...

I know of some pepboys shops that I don't trust, while others I'd definitely take to (know the ASE certified technicians there)...

so, how about that rough idle?

seems to have been reduced slightly with the new tensioner not much, when I bring my car back to my house in the summer my dad will replace the rotor since its like $5 for it at a local autozone =) Now I have some confusion now actually. What the heck does a v belt do on my car anyway I know its important =P and I know that the serpentine belt powers the alternator and a/c and probably does other stuff too hehe.

Tune up is;
1. plugs
2. wires
3. air filter
4. Fuel filter
5. motorvac (about 800% better then the stuff you put in the tank)
6. cap & rotor
7. Cooling flush
8. check pvc system

those are for factory set-up, mine is very different. Also for a rough idle, check your ais motor, tps, and map sensor. Also an injector may be plugged.

Tune up is;
1. plugs
2. wires
3. air filter
4. Fuel filter
5. motorvac (about 800% better then the stuff you put in the tank)
6. cap & rotor
7. Cooling flush
8. check pvc system

those are for factory set-up, mine is very different. Also for a rough idle, check your ais motor, tps, and map sensor. Also an injector may be plugged.

1. Got my plugs replaced not too long ago that took care of 90% of the problem from what it was before.
2. Wires im going to do myself when it finnally warms up I think I could probably handle those on my own =)
3. Air filter just got that done
4. On my to do list
5. I have no idea what this stuff is could you please describe.
6. Also on my to do list.
7. Did that last year
8. Again on my to do list =P

1. Got my plugs replaced not too long ago that took care of 90% of the problem from what it was before.
2. Wires im going to do myself when it finnally warms up I think I could probably handle those on my own =)
3. Air filter just got that done
4. On my to do list
5. I have no idea what this stuff is could you please describe.
6. Also on my to do list.
7. Did that last year
8. Again on my to do list =P


A motorvac is a machine that they hook up to your car, it flushes out the entire fuel system, lines(pressure and return), fuel rail, it also cleans injectors, and removes carbon from the engine. I have done this on my car and i noticed that i have a tad bit more power now. I did a before and an after with this, i checked the plugs before i did it, all fouled and worn out, just for poops and giggles i left them in and did a motorvac on it and then checked them again, they looked like new all shiny looking and sparkly, but they got changed anyway. Your local shop may be able to do it. it usually costs like 50-65 dollars to do. The injector cleaner that is used in here is soo strong that it cannot be put in the tank or it will kill the pump(eats up carbon, electric motors have carbon brushes)