Cranks but wont start

Here is the case. I have a corolla '96, AE101, 1.6L, MT, with 120K km. On it and im the 3rd owner. Its with me for about 2yrs now. Its a well maintained car in terms of all preventive maintenance is concerned since I bought it. The cars performance is great and runs very smoothly without any symptoms of any trouble. Suddenly one morning, Wednesday last week, when Im about to bring my kid to school, the car wont start. It have a strong crank but did not go through. After sending my kid to school by my motorbike, I passed through a mechanic and ask him to go with me to check the car. He made a series of test and found that no spark was coming out from the spark plugs. He suspected the distributor, so he took it out and asked me to bring it to a repair center for check up and necessary repair. As the repair center checks, it seems to be ok. Sparks are coming out though seems to be weak and parts were soaked in oil. He also found a part (condenser as he calls it) partially melted and need to be replaced. So he replaced that part plus the oil seal. The new oil seal doesn't fit too good with the shafting so he replaced the shafting too with his spare one free of charge. Cleaned everything, assemble, test and spark gets way better.

i get back home with my repaired distributor, called the mechanic and put back everything in place. We tried to start the engine, SAME RESULT. He then checked all the fuse and found nothing defective. Then he tried it himself to turn the ignition ON, then he noticed that the check engine light was off. Suspecting the computer box (ECM) and not too sure of the next step to check, he went back to his shop to get his manual and diagrams. Then gives me a ring to tell me that he got lots of stuff to check on the car and preferred to bring it to his shop. Since its already late, we decided to bring the car at morning the next day.

the morning as Im preparing the car to bring on the shop, I tried to start the engine. Suddenly the check engine light was on and it starts on one shot! Check engine lights turned off when the engine starts running. So I called the mechanic telling that it goes, he recommends to 1st observe the car performance and note everything. The following days were good. Running smoothly and everything seems to be okay.

then a week after, at Wednesday morning (Wednesday again!), Very same thing happened.. With my day was filled up with work that day, wasn't able to inform the mechanic. Instead I asked my dad to attempt to start the engine every now and then throughout the day. The day passed and it didn't start and check engine light didn't turned on.

then yesterday morning (Thursday! ), 1st I did off the bed is to try to start the engine! And yes it starts in one shot with the check engine lights off as it runs. I let the engine warms up 4 about 10 to 15 mins. Then went back to the car, turned off the engine and tried again. And as I turn the key, the check engine lights didn't comes on and fail to starts again.