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Discussion Starter · #1 ·
'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?
 

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Discussion Starter · #2 ·
after further inspection I noticed discovered that the vacuum line from the egr vacuum modulator goes to the thermo switching valve and subsequently to the intake manifold and to the distributor. So I'm totally at a loss now, anyone familier with these confounded vacuum emission controls I would appreciate any input.
John
 
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