1995 Honda Prelude Engine Pinging

Hi, my 1995 Honda Prelude H22A JDM version is pinging. When I start the car in the morning, there is no pinging. But once it idles and comes to operating temperature it starts to ping in the following manner. The pinging can be noticed when I suddenly depress the gas pedal with A/C on even in parking mode. The pinging is getting worse and now a days I don't even have to suddenly depress the gas pedal. What all it needs is to switch on the A/C and put my car in drive mode once the car is warm. Initially, the above problems were just limited to warm days. But now they are obvious even at nights after taking my car around in my town for say 20 minutes or so. Once the car is in motion there is no pinging. But what is even more disappointing to note once I start to move is the obvious loss of power with the A/C on.

I recently got the engine overhauled. Changed timing belt, tensioner, balancer shaft belt, some piston rings (as they were broken in cylinder no.4), gaskets and skimmed the head. My mechanic says the timing is perfect. He says that he neither advanced it nor retarded it. He is suggesting to clean the injectors and see. He is suggesting to change fuel pressure regulator also. Already he changed the closed position volts of throttle position sensor from 0.47 to 0.492. I thought the pinging actually got worse since then. I don't know what to do. Spent lot of money on it. I always use the higher octane gasoline only. Please help. What do I do? Your inputs will be invaluable for this bankrupt, dejected fan of 4th generation Honda Prelude.