Toyota Repair: coolant lose & irractict idle&varing heat, combustion chamber, internal combustion

Question
1994 toyota p/u,4x4,4 cyl.. when i bought it used i was told the headgasket had been done and it may have a leaking rear main seal.this was at 115,000 miles.125,000 miles my truck started to act up so i did a tune up. cap,button,plugs,wires,air filter, thermostat. since having done this it will run fine at times but then it will start to idle irractically. 500-2000 rpm, no heat will blow . then just as quick it will come out of "it" and run right. however it will loose anti-freeze but it is not showing in the oil like a normal head leak. any ideas would begreatly appreciated.

Answer
A blown headgasket does not always leak into the engine oil, it can leak into the combustion chamber and be burned by the combustion process, this is probably the cause of the erratic idle, I would recommend having the engine checked for an internal combustion leak, this can be done with a chemical test or with an emission control analizer(more accurate)so before doing anything else have it tested.
I realize that you were told that the gasket had been replaced but the cylinder heads on these engine are also prone to cracking, so the gasket may be ok but the head may have a crack in either the intake or exhaust port.