I've been testing this thing for a couple weeks now and have yet to find a solution. The engine is a VX200TLRA. With Rodbolt's help, I found I've got a 2003 block. As the title states, I've gone from running 5200-5400 RPMs at WOT down to 4500RPMs. Sometimes it'll get up to around 5000RPM before coming back down other times it'll get up to 4500 and stay there regardless of throttle inputs. I've tested the fuel pressure on the water and it remained 35psi from engine start all the way up to 5000RPM and back down to 4500RPM. I have replaced the VST filter as well as the pressure regulator screen...both had debris on them originally. I also tested the high pressure in the driveway at idle and used a vacuum gauge to test whether or not the fuel pressure regulator would lower pressure when pulling a vacuum. The fuel pressure decreased down to around 30psi as I pulled about 30kPa (~8" Hg) of vacuum. According to the manual I've got, this is expected. I replaced all 3 lift pumps (not 100% they're good...I tested the vacuum on them dry but that isn't worth much since the seals weren't wet). Not sure of another way to test them. I've pulled the O2 sensor, cleaned, replaced all gaskets and o-rings. Tested the O2 sensor and it will fluctuate between 0.3 - 0.6VDC with the engine over 140F. I tested it at idle according to Seloc. I'm not sure which way to proceed. I did check the TPS and it is good (adjusted a small amount, now at 0.51VDC at throttle closed). I did a link and sync in the process. The only thing I've altered a bit is the throttle linkage. When I had the hotfoot set up before, even when I got to WOT, the throttle valves would not be close to fully open. I lowered the stopper so the roller would just hump the steep part of the armature and get to the top side (it's set up so that the distance thrown on the cable will only minimally alter the throttle valves when it gets to that part). Thanks for any thoughts or ideas.
