rpms when idling

I have a 1991 gmc 4x4 with the 350 and 400,000kms. When I am in drive it idles at 200 - 300 rpm. Is that low? Now my question is that when in drive and sitting at a light or in park when the engine is hot my rpms drop to 150 and goes to 350 up and down as if it is surging( for a lack of a better word). When i am driving the rpms are fine, about 1100 - 1200. Any ideas as to what my problem could be? I read another thread about someones throttle body sticking, could this be my problem? If it is are theyhard to clean yourself? Thanks in advance!

I suggest getting a second tachometer and checking the accuracy of your tach. 200-300 is VERY low, and I wonder if what you are getting is an accurate reading. Your engine is computer controlled, if I recall correctly, and idle speed is controlled by the computer via the air bypass solenoid. It and the throttle body can be cleaned with Gumout, etc. Be careful, there is a mass airflow (MAF) sensor among the hardware, and possible other sensors, that you need to be gentle with.

I'm having the exact same problems with my 1990 305. It idles very low and surges. I am going today to check the egr valve.
I would suggest to you to look for vacuum leaks, run some injector cleaner through, check all ignition parts, change fuel filter?, check timing, may need valve adj. or have a bad cam lobe...just some ideas. Good luck.

the 91 gmc it surged every once and a while. I changed the plugs to a racing plugs worked good,6 months later it happened again. I figured it worked once try again checked the plugs two where misfiring the I when the bosch plugs worked fine.Then about a 6 to7 months later did it again, same problem as the first one. Then I went and got factory plugs not a problem.

Well I changed the EGR valve and WOW!!! what a differance. The truck now idles at the proper rpm, it runs smoother and is all in all much nicer to drive(smooth).