ebnub

I have a very slight roughness at idle and no check engine light. I found instructions on checking the Idle Air Valve by jumping the TE1 and E1 terminals on the diagnostic port and the engine's idle increased and decreased within 5 seconds as it said so apparently the IAV is ok. I couldn't remove the IAV without stripping the screws so I sprayed a 1/2 can of carb cleaner into the port next to the throttle plate while the engine was running hoping to clean it a little bit anyway. The engine coils seem ok, there was noticeable engine change as I unplugged each one individually. Air filter is clean, no coolant or oil loss. Looking for more ideas. The issue is noticeable whenever the car is sitting at idle including sitting at a stoplight.

Heres where I found the instructions for checking IAV: http://www.autozone.com/repairinfo/r...00c1528009269b

PFB

Don't exclude motor mounts as a possible cause of your symptom.

ebnub

Thanks for the suggestion, I'll check them out. I can understand how this would give a feeling of a rough idle but would it also translate to the tachometer needle? I can see the RPM needle moving very slightly at idle.

vintagelex

If you see the rpm's going up and down a bit at idle, I would try replacing the fuel filter. They're pretty cheap and it can't hurt to have a new one on there anyway. Also maybe cleaning the throttle body would help. Any idea on when the spark plugs were last changed?

If there's no check engine light then I would try these things first, because they're relatively cheap and they should be done as maintenance once in a while anyway. Also a good idea to check the engine mounts, like PFB suggested, but I don't think that would cause the idle to fluctuate - it would just cause vibrations.

ebnub

I changed the plugs less than 10,000 miles ago with NGK iridium and cleaned the throttle body at the same time. Fuel filter was changed around 10 years and 120,000 miles ago so yeah I should probably do that.

ES300NZ

sounds like timing to me. perhaps the timing belt has stretched enough to put the engine out 5-10 degrees. Cos, if it's not spark, and not air, and not fuel (fuel pump?), then it's most likely timing. It could also be that the tensioner wasn't replaced when the belt was last done, (you can cheap out on that if you want), and it's cause the motor to be out of time.

EPayne42

I agree with ES300NZ, but also try spraying some carb cleaner around the engine. Spray around the intake manifold gasket area and around vac lines. If you hear any change in the engine rev, you got a leak. The carb spray test should help you pinpoint.