Solutions for engine pinging/detonation?
 

This isn't on a Honda, it's on my wife's 1996 Toyota Corolla, which has a 1.8L engine, pretty similar in technology to the early OBD-2 B18B engines, except it just rotates the opposite way

Anyway, it's been having a problem with pinging when lightly pressing the gas pedal for awhile now. I tried running some Seafoam through one of the vacuum hoses, but the problem still persists. I may try it again because I think I didn't use enough of it last time.

But is there anything else I can do short of pulling the head off and cleaning out the carbon? I even tried running some 89 octane fuel for a couple of months instead of regular 87, and even that didn't help.

I don't know about auto repair shops in Canada, but here in CA and elsewhere in the U.S. repair shops have a closed loop system that injects a solvent-based cleaner into the intake system that is supposed to remove carbon deposits from the combustion chamber. Carbon build-up shrinks the volume of the combustion chamber and raises the compression ratio. That CAN cause your ping, but you may have other causes as well- maybe problems in your ignition system that could be found in a diagnostic scan at the repair shop.

There isn't enough antiknock difference between 87 and 89 to be sure you don't have carbon compression increase.
Run a compression check first to see if your compression ratio is in spec.
All 4 cylinders. Try adding gumout or injector cleaner to your fuel or fill it with real high test (high octane) gas. If the pinging is still there you may have a spark plug problem or a ignition advance too far. That means first adjusting the advance to spec or perhaps 2 degrees retarded. Then R&R the plugs.
If the knock goes away you probably do have carbon buildup to the extent that compression is too high for regular.
If it doesn't, you either have a lot of carbon buildup or...

If that doesn't do it then you need to check for leaking head gasket. Water or oil into the cylinder will reduce your octane rating. Especially if carbon buildup is enough to raise your compression beyond help.
Try those first... After that it gets tougher.
good luck.

Seafoam it again. Run 93 octane? If you do the math it's only a couple bucks more each fillup.

According to the Haynes Repair manual for Corolla years 1993-2002 that I kept when I had the 2000 corolla...

Trouble shooting #16 : Pinging or knocking enging sounds during acceration or uphill

Possible causes:
1. Incorrect grade of fuel
2. Ignition timing incorrect
3. Fuel injection system faulty
4. Improper or damaged spark plugs/wires
5. Worn or damaged distributor components
6. EGR valve not functioning
7. Vacuum leak

I once had serious pinging problems at all speeds because aftermarket spark plugs were out of spec. It was fixed when I got OEM spark plugs from toyota. Unfortunatly, dealer sells for more expensive. Maybe you should check timing or drivebelt to see if timing isn't off or uneven tensioned.

Check the EGR valve and associated hoses. I've had them go bad before but I've never owned a Corolla. Vacuum leak is another good place to start, especially if your car has a vacuum spark advance.

When working through lists like these, I usually start with the least expensive items first.