high idle after spark plug change
 

Hi everyone, I just changed my spark plugs on my 99 gs300 to denso iridium and now the car idles at around 1200 rpm. Why is this happening, someone please help.

I just changed my plugs this weekend. Is there a possiblity that something dropped into the throttle drum area and worked its way down beneath it... the one that your throttle cable connects to??? I suggest you take the plastic cover off, take a flashlight, and hand operate the throttle by pushing down on the throttle cable... did I mention "with the engine off". Carefully look around this drum and see if anything is causing it to bind. My spark plug change did not affect the idle at all..... it just improved performance :o)

Whoops..... I thought you had a gs400, thats what I have. Although the 300 has a similar setup. I wonder if when you removed the read shield over the plugs, something.. dirt, etc, worked it's way south of the throttle spring????

When you removed the intake to replace the plugs, you might have forgot to connect a vacumn hose.
Did you use new gaskets?

I forgot to mention that I also cleaned the throttle body b/c it was pretty gunky and I used the same gasket.

You might have an air leak. Get a can of brake clean and spray it around throttlebody gasket area. If the idle changes, you know the gasket is bad. :)
JPI