Expert: Roland Finston - 7/2/2011

Question
QUESTION: only idles rough, otherwise runs great. it has 90,000 miles on it. 1st i replaces the motor mounts, didnt fix prob so i changed plugs. still not fixed, I took to a shop and they seen the pulley on the power steering had chunks missing and thought that would make it out of balance causing that. still didnt fix the rough idle! now they said its the belt tensioner because the bushing is out. i dont know what to do!! please help me

ANSWER: Hi Todd,
A bushing on the belt tensioner would be important to replace so as to not have it lock up and loose the belt action but I don't know about causing a miss. Have you tried to get a fault code read using the ignition switch: On-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. The mileage reading in the odometer window may change to show a 4 digit number. If so, let me know and we'll go from there. Or go to an Autozone parts store for a free readout using a plug-in reader.
Roland

---------- FOLLOW-UP ----------

QUESTION: the engine doesn't seem to have a miss at all. all cylinders were checked, all are firing. they checked for codes and there was none. steering wheel shakes at idle at times, and hood always shakes until you give a little gas. the shop is pretty sure its the belt tensioner. I have a problem replacing that when the part is $426 and 2hrs of labor without a guarantee it will fix it. before i replaced motor mounts you could make the vibration stop by putting the tranny in neutral and park. now it does it all the time unless you press the gas or are driving..

ANSWER: Have you checked for codes? Which engine do you have?  What evidence is there that the problem is the timing belt tensioner (which I now suspect is the tensioner they are speaking of based upon the price)?  I can't believe the part is $426, what is going on here? Let me know the answers to those questions and we'll go further.
Thanks for the rating and nomination.

---------- FOLLOW-UP ----------

QUESTION: we have checked for engine codes and there wasnt any. when they replaced the pully and belts they said the tensioner wasnt steady when belts were removed, he said it swayed back and forth about 4" which is caused by the bushing.. could a belt tensioner cause a rough idle?

Answer
Hi Todd,
I can believe at wobbly timing belt tension would produce a rougn timing IF the change in tension was great enough to affect the timing of the valves to the crankshaft/timing of the spark. But I can't understand a part at that price. I wonder about the advice you are getting. How about a second opinion.
The only other suggestion I would have is that you check whether the exhaust gas recirculation valve might not be closing tightly at idle due to a build-up of crud on the stem or at the valve/valve seat interface. If that were so it would cause a rough idle but not set a fault code. So look into that possiblity. You didn't tell me which engine you have so I can't offer direstions.
Roland
PS You are entitled to rate/nominate me again if you so-choose.