So i recently bought my 04 TSX with 46k miles and I have noticed my first problem. After the car is warm, usually driving for 15 minutes or so on the freeway, I get off the freeway and stop at a traffic light Thats when the problem starts, as I am sitting there I notice the RPMs starts to oscillate. It usually oscillates from about 500 to 600 RPM but I have seen it jump as high as 800. Also I noticed that when the RPMs are around 500 the car will vibrate, enough to where the change in the cupholder starts to rattle. When the light turns green, the car seems a little laggy and will take more pressure on the accelrator to get it moving again.
I was curious if anyone else has had a similar problem or if anyone might know whats wrong. Please let me know if you need any more information.

 

500 is too low for idle. The first cheap and easy step I would take is to have the battery tested at an auto parts store. It's free.

Any check engine light(CEL) flashing?

 

I have an 07 and the lowest I've seen it idle is 600rpm. If it's idling below that, something is probably wrong.

 

I would suggest buying a scan tool. You can pick up an Actron 9145 off amazon for $99.00 and if your car is throwing a pending code (one that has not set off the mil or the check engine light) you will be able to tell what is wrong. If I had to guess at your problem I would say it could be the idle air control valve, upstream o2 sensor, or any number of vacuum hoses that may have a pinhole in them. Do yourself the favor and buy the scan tool it costs no more then an hour at the shop and it will work on all your cars.

 

Took the car in and they said it was an O2 Sensor problem.
Luckily i didn't have to pay anything to get it diagnosed.

 

FYI, there is no Idle Air Control solenoid on the TSX. It just uses to drive by wire throttle to control idle.

Glad you found the problem. Did you get it fixed yet?