'85 corolla, 4ac engine. Spark knock is occuring, but only after I shift and reapply the gas, and only for a few seconds. I can be in any RPM range, and if I let off the gas and then reapply, it will knock for a few seconds and then quit. I checked the egr valve, it opens and causes the engine to run rough immediatly, I don't see any obvious vacuum hoses amiss. The only thing I can think of is the vacuum hose that runs to the carb and spark retard from the egr vacuum modulator is not holding a vacuum, even when I plug the part that goes to the carb (duh). At least I think it goes to the spark retard, according to the VECI label on the hood. Any ideas?