my suggestion on finding a vac leak is to temporarily cap off all the ports on the intake or throttle body. do it very deliberately - make a list, number and label them with painters tape or duct tape. see if the noise goes away. if so, add them back one at a time until you find the culprit.

caution - when you cap off the brake booster, you won't have power brakes. also others control 4wd, cruise, vent controls, egr, evap system, etc. and you'll probably get some CEL codes that might require PCM reset.

 

Has anyone else fixed this type of problem with the power steering cap? I just dont see it being related to the plenum since it doesnt hardly have any miles on it since repaired. I know theres vacuum lines running through to the dash, anyone have any advice on tracing those? Also, the misfire may be caused by the O2 sensor from before the plenum was repaired. I havent pulled the plugs and looked at them yet, but is there any way to test the O2 sensors?

 

Buy a cigar, a good one, enjoy it and blow smoke around the engine. Find the leak and enjoy a great cigar, maybe some whiskey on ice. Just saying

 

After a plenum repair or during, the cat and o2's should be replaced.

 

My cat was replaced just before i did the plenum. Should i still replace it? What happens to the cat with the bad plenum? I pulled all plugs tonight and they look horrible. Im not sure if it was caused from Pre-Plenum problems or not, but i kinda planned on replacing the O2 sensors soon anyway. Im gonna get new plugs and the O2 sensors and hope that fixes the misfire. When i get a chance I'll do some more searching on the vacuum leak.

 

Depends on how bad the plenum was blown and how long before you fixed it after you replaced the cat. And if the o2's were not replaced, there is a good chance they were having the pcm dump in more fuel, which will also not help the cat.

 

Those are some nasty lookin plugs. Way overdue. Might as well go for wires, cap and rotor too.