Disconnect the negative side of the battery for a good 30 mins. I remeber my car did something similar when I changed my plugs. Sometimes when I would stop at lights, the revvs would bounce from 500 to 1500. I think your car is just trying to learn the new plugs. What is the part number on the new plugs?

 

If you did disconnect the battery cable, that is what caused it. When you reset the ECU, it takes a little bit of driving for it to learn its idle settings again. Perfectly normal and should go away after a bit of driving. It will drive pretty much normal, but when you stop its idle will be low and will hunt a lot.

The car doesnt need to learn anything regarding the plugs.

If it doesnt go away, then make sure your plugs had the right gap for the car.

 

Thanks guys. I figured that is what it might be and makes sense to me since I'm an engineer hehe. I don't want to mess with the MAF which I found out meant the Mass Air Flow sensor. Last night it was idling a little better at 600-700. I guess I am used to it idling at 1000+. Maybe because battery or spark plugs were bad?

Guy above, I replaced them with the same stock Densos - exact model and everything.

 

It should only ever idle at over 1000 RPM when you first start it. Normal idle after it runs for a bit should be around 700 rpm. So it sounds like it was just the reset that you were seeing.

 

If one were to be into saving gas, would the lower the idle be better? Is there a reason why cars idle at 500+ rpm? Why not idle at 100 rpm or less? Maybe this is a dumb question? hehe.

 

the 2az-fe (scion tc motor) idles between 690-710rpms with slight drops down to the 500rpms depending on engin load at idle(lights on,heater fan running rear defroster even cooling fans ect.....) all can play a part on low idle at times. iv watch this happen on my digital rpm shift light controller i have installed in my glove box

and about differnt idle speeds all motors are not the same some need higher idle speed and some need lower speeds. old 60's big blocks idle around 400-450rpms and top fule dragster idle around 2200-2500rpms. every motor and setup is differnt.

 

A 4 banger idling too much lower would stall out as well.

 

my car idles at almost exactly 0725rpms. thanks digi tach!