BMW Repair: Overheating / Idle Problems, losing coolant, piston rings

Question
I drive a 1988 320i bmw, the engine was recently been overhauled due to its overheating problems, piston rings has been changed and same with the gaskets and the cylinder head had been resurfaced as they call it. water pump is replaced aswel, for the first two weeks it went well and temp had not gone up but after those weeks it again started to emit white smoke and starts to overheat and during the cruise there are times that the temp gauge will suddenly be going to a normal reading and sometimes moves unstable. I'm not losing water and no leaks either. and with the idle, it is stuck in 1100 rpm on a normal start up. can you give me any ideas what to check into? do i need a high scan for the computer box? thanks and hope to hear from you soon.

Answer
The temperature needs to be checked with another gauge.The car is twenty years old and being in a hot climate it does tend to dry and make gauges weak and read incorrectly.Another issue is the body ground.Besides the one at the battery the grounds under the dash.Ground wires are brown in color.
Clean the Idle control valve,throttle plate and adjust them.If the valve cleaning doesn't cure it you may have to replace the idle control unit/idle control valve as well.
If your not losing coolant the gauge needs attention,the smoke you see maybe condensation from the exhaust.