short pre-lude. I bought this 99 catera for $1300 and it is clean, however, it had a random misfire code P0300 and misfire codes for cyl 2-6 none for cyl1. Also i had a P1509 idle control system high fault.
The previous SUCKER had sprayed the entire lower-upper and plenum with Permetex Spray N Seal Leak Repair, coated fuel injector at port with silicone, all for nothing appearently as the problem forced the sale to me.

(what i have done so far)

pulled lower, upper,plenum and injectors. cleaned everything well checked for cracks installed new gaskets and seals. new plugs and tested coil packs. replaced all vaccuum lines from brake-can to vaccuum resivoir. cleaned throttle body and new air filter. replaced one valve #90466214 at the rear of plenum and tested vaccuum actuators. ran lucas injector cleaner and all this only fixed the P1509 idle iar system fault.(YAY)

Now the only codes are the random multiple misfires. now i am getting an occasional backfire(very mild) and misfire at an idle. seems to clear-up when in the throttle. suspect a vaccuum leak in the rear of motor in or around the PCV oil seperator. Whats a good method of isolating this system to determine if the seperator is the fault?