My 04 LS Modern Lux has about 115k on it now. Replaced 8 spark plugs about 10k miles ago since my engine idle low at around 400rpm.
My engine idle is still low after the new spark plugs, any ideas on why it's low or is there a way to increase it?

 

Is it causing a problem? If not, I would leave it alone. Also, are you sure your tach is correct?

 

Only concern is if the rpm is around 300-400, engine is shaking the steering wheel a little. But the car drives fine.

 

Just to see if this is the famous low engine idle issue, does the problem fade away when you turn on the headlights and foglights? (or AC)

 

Going to give it a try. Never thought about it.

 

Nope, fog light or ac is not the issue. This is happening randomly. Maybe it's the cheap gas but I always use 93 premium from Shell.

 

I know they are not the issue, but does idle come back to normal when any of those two are operational?

 

Did the low idle really start at spark plug change? If so then it may be something was messed up during the process of installing the plugs. Go back and inspect all rubber fittings, vacuum hoses and electrical connections anywhere in the engine bay and particularly around areas that might have been touched/bumped during the spark plug work. Look for disconnected items or just loose or partial or torn connections in any of the air/vacuum hoses and or electrical connections. its worth a shot to double check if the low idle actually started right after the plugs were replaced. I assume the plugs are right type and were installed properly.

 

The happens before the plugs was changed also. I think it's the cheap gas.

"I know they are not the issue, but does idle come back to normal when any of those two are operational?"

Nope, seems like it would stay around 400rpm. I think it's the gas.
GRAND_LS_4, where are you located in NOVA? I've lived up there for 20 years.
Currently reside in Richmond VA

 

Did you fix your problem?

 

Dirty throttle body can also cause this. its not a good thing for your car to idle too low. Oil circulation and power to the accessories is important.

 

Disconnect your battery for 24 hours. The RPM will return back to it's normal place. That's what worked for me.

Good luck!

 

clean you t/b then disconnect your battery for 15 minutes then take it for a drive.it may run a little rough for a couple of minutes as it burns the cleaning compound out.

 

I cant fix this problem, I did so many things but the RPM stays the same low, I did clean the throttle body, change spark plugs for ngk iridium, clean MAF, put lucas fuel igector cleaner, 2times disconnect battery, look for the air leak in intake, no luck.
Actually the problem appears, after I disconnect the battery, for 1 time after I bought the car.
Cant get after 200 mile run, evap system monitor ready.

 

you could go to the dealer and have the ecu reflashed.