Lexus Repair: 1992 Lexus Sc300 Low idle and rough drive, blown head gasket, 1992 lexus sc300

Question
Hi. About 6 months ago my car would not hold an idle all of the sudden, I would have to put it in neutral and keep the gas going when I stopped. I let it sit for about 6 months and took it to get repaired, they did a tune up and changed the front o2 sensors, also turned up the idle supposedly . Now the idle is really low, has a very rough idle at times and heavey white smoke when it rough idles (when stopped vibrates heavily). What do you think the problem is? THe mechanic said the fuel pump is fine.

Answer
BLown head gasket. Do a compression / leak-down test to confirm that on a warm engine.
Clean the throttle plate, idle valve & EGR valves to stabvilize the idle. You can turn the idle to wherever you want - but regardless of what you do the ECU will idle the engine at whatever it thinks is then applicable idle speed.