Diagnosing rough idle

[steppinthrax]

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.

 

[Demon-Xanth]

Does it have a cap and rotor or a DIS?

 

[steppinthrax]

Originally posted by: Demon-Xanth
Does it have a cap and rotor or a DIS?

All coil pack. No cap rotor mechanical ignition system b.s.

 

[programmer]

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.

 

[olds]

Vacuum leak?

 

[helpme]

Bad throttle position sensor and/or wiring?
Bad Idle air controller and/or wiring?

 

[Fenixgoon]

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.

 

[steppinthrax]

Originally posted by: Fenixgoon
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.

No SES or CELs.

 

[steppinthrax]

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.