I have an 6 speed 04 Z with a swapped DE from JDM of California (my old engine blew), anyways today I was driving and while at a stoplight my rpms went from normal idle to practically zero, I just shut my car off, turned it on when the light was green and drove it the rest of the way home (1 mile) then in my driveway I let it idle and 30 seconds into idling the same thing happens, rpms go from normal idle to practically zero, this time I kept it on and it stood close to zero for a quick second then went back up to normal idle and I just shut it off after that, this happened before so what I had done was clean, most of the grounds I could see, clean the throttle body (it was full of gunk around the flap and wouldn’t allow it to close fully so now it’s just a TAD bit open and not fully closed) changed out the intake manifold gaskets, changed both valve cover gaskets, got new spark plugs, and checked the resistance on every coil pack and all of them were around 1.5, I have no idea what could be causing this issue, I also have no CEL light or anything on, I have a feeling it might be because my throttle body flap isn’t fully closed and I have to drive it so it can re learn the positioning again but I just wanted a second or third opinion from the forums on what might be wrong, and I had changed the right valve cover and gaskets because I had a CEL for a random misfire but changing that fixed it, I also noticed that my hose going from the intake manifold to the left valve cover is pretty cracked and the same goes for the hose going from the intake manifold to the battery compartment for the brake booster, as a “temporary” fix I put heat shrink around it to hopefully cover the cracks to see if it would fix my issue of a possible vacuum leak of any kind

 

1) Any time you have a problem try to understand what you did or what changed since it ran well.
2) When you changed the intake manifold gaskets did you torque them to 48-60 INCH lbs and RTV both gasket sides?
3) Since you suspect a vacuum problem invest $12 dollars in a vacuum guage and tap into the intake lines. It should read around 22-25 with very little fluctuation after running 10 seconds.
4) Change your brake booster hose. At this point you're out only $35. If it works, life's good, if not, you have a cheap problem you can rule out.

A word to the wise- if you touch your throttle body(s) without disconnecting neg battery you'll likely need a shop. GL

 

What do you mean exactly by I’d need a shop?