Erratic idle speed

[gtorick]

My 92 Geo seems to run fine at highway speed.... but at idle with a/c off the engine surges constantly...i can find NO loose vacuum hoses. Any ideas?
Thanks
Rick

[SchlockRod]

1. Check Codes from ECM
2. Check your throttle body gasket for leaks. Spray Gumout at the seam between t.b. & manifold at idle; if the idle changes when you spray, it is getting sucked in (along with a lot of air).
3. If Test 2 is positive for leak, replace the t.b. gasket.
I changed my gasket and the problem went away immediately.
To get the old gasket off, take a piece of copper tubing and flatten it in a vise, then grind the flat end to an angle and wire wheel it. This makes a great gasket scraper for aluminum surfaces - won't gouge them.
I put a thin coat of Permatex Form-a-Gasket sealant on both sides of the new gasket and let it get tacky before installing, but some will probably say it makes things a bear to clean up at disassembly. I say that's what the copper scraper is for.