Toyota Repair: carbon build up, jumper wire, diagnostic check

Question
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Followup To
Question -
I have a 93 4 cyl 2wd Toyota p/u with 142K with a pinging problem. I was told it was probably carbon build up. My mechanic used Run-Rite 4 part fuel system cleaner. Ran great for 2 weeks and know it pings on acceleration and highways speeds again. Worse whne its over 100 degrees outside. Is it safe to do the fuel system cleaner a second this soon? Also, what should the idle RPM be at an idle? It's @ 1300. Mechanic advanced it slightly to get it to run better. He said that was still within the specs. Premuim gas seems to make a difference. I was told to try a fine mist spray of water into the air in-take. What would be the best thing to try next? The mechanic said there was nothing else wrong with it. Many new parts (radiator, timing chain, water pump, AC compressor etc. ) Thanks for any advice.
Answer -
The idle should be about 750 RPM, the timing may be too far advanced, it should be no more than 10 degrees with a jumper wire on terminals TE1 and E1 at the diagnostic check connector.


The idle has been adjusted down to idle @ 900. 750 was too rough. No change in the original pinging problem. A second Run Rite cleaning was done @ 5 weeks after the first with no change. Any other suggestions?

Answer
Have the engine compression tested, it should be no more than 180psi, a higher reading indicates a carbon problem a reading lower than 140 indicates that there is a loss of compression, all cylinder readings should be within of about 10psi of each other, this simple test will give you a good indication of what the problem may be.