Its a '96 Corona with original 2.0li 3S-FE.

Work done:
Due to oil leaks and abnormal heat emanating from the engine, the not-so-good mechanic suggested changing the cylinder head gasket and cylinder head cover gasket. He said that the cylinder head (the block containing the valves) as well as the valves needed to be machined to correct imperfections.

Symptoms
Once he put it all back together, the car never felt or sounded like its old self. Sure, it did run smoother and better than before but the engine developed a shiver-like shake. This happens on idle and the tach dips down to 500 rpm from 1,000+rpm. This intense shiver only happens on idle and occurs infrequently. The car also sounded differently from the outside. It sounded its having an asthma or hard time breathing. The not-so-good says this caused by the newly machined having to seat themselves properly???

The not-so-good mechanic also says its the car's timing which is beyond him. So he suggests a shop in Banawe that quickly declared its the "TPS" that needed replacing. So they replaced it with one meant for an Altis since they don't have a specific one for the Corona. The car still shiver but not as intense as before.

What is the problem with the car? Is it repairable? If so, which repair shop that can be trusted can do the job?

Also, its worth noting that car emits white smoke (a sign its too rich in the fuel mixture) on start ups from a cold engine only. It also seem to consume more fuel (the shop increased the fuel consumption to minimize the shivering of the engine).

Is it possible that the intake camshafts and pulleys were not torqued and assembled (in correct screw order) which might be causing all these apparent "timing" and shivering problems? Because all the parts replaced except the gaskets were all in good working condition before the disassembly.

Thanks to anyone who replies to this long story.