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Diagnosing rough idle

S

steppinthrax

Diamond Member
Ok this is the deal. I have a 99 Camry with about 30K on it. I just bought it last week. I notice when the car is at idle the RPM needle vibrates a bit at idling RPMS in response to the engine's rough idle. You can't really feel it because the car dampens it a lot but you can feel it in the brake pedal as well as see it on the RPM needle that shakes.

I changed all 4 spark plugs and the situation seemed to impove a bit. But in this case the rough idle is intermitent. Sometimes when at a stop the neelde shakes and sometimes it dosen't. This is with the new spark plugs. So I'm trying to find out what else needs to be checked/changed. I don't just want to keep changing parts.
 
spark plug wires?
EGR-type valve?
Bad motor mount(s)?
Bad tranny mount?
Clogged injectors?

Just a few of the numerous possibilities. Personnaly, I've had both bad/old/cracked plug wires, and a bad motor mount cause rough idle. The former also caused a small loss of performance at speed.
 
do you get any CEL's or anything?

i had a rough idle on my passat that turned out ot be a bad coil pack + ignition control module, fwiw.
 
Thanks guys I will check those compoenets when I get home. The reason why I never changed the spark plug wires is because they are 54 dollars a set (cheapest) anywhere I go.
 
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