pinging when the throttle is slightly opened under light acceleration around 2200rpm after engine is operating temp. Its coming from top end. This just started after I adjusted the tps to clear a code 51 that I inherited when I bought the car. After I cleard the code I set base timing. A couple weeks before that I adjusted valve clearances to clear up some valve tick. The car runs fantastic. The ping started only after I cleared the 51 and set the base timing. 88 n/a with pace setter header, no cat , lots a miles but a hg not long ago w/arp from prev owner. Any ideas would be appreciated.