1986 rx-7 NA
I just did the S4 to S5 conversion and removed all emissions stuff and rats nest. I have not had time to fab up an exhaust system so it dumps right after the header. I also have the UIM set for the higher rpm range. The car will not idle at all.
I have checked there are no vaccuum leaks. No unplugged wires that are not supposed to be unplugged anyway. I have tried adjusting the idle screw on top of the throttle body nothing changed. The car revs just fine but once I let off the gas just dies. Any thoughts or ideas?

 

What does "the S4 to S5 conversion" mean exactly?

S5 engine block w/ existing S4 accessories, wiring, sensors & ECU?

S5 engine with S5 accessoried, wiring, sensors & ECU?

S5 intake manifold on S4 block?

 

I swapped intakes. Thats all. Everything else is s4 TB, injectors, Air meter.

 

Ok, then it's most likely the UIM hitting the rear iron. A portion of the iron has to be ground down to allow clearance. When I put an S5 manifold on my S4 NA engine, I had to take it all back apart to grind even more away. The first time I tried to run the engine, it started & immediately stalled. The UIM seemed like it was sealing against the LIM, but there was just enough of a leak to cause problems.

Writeup links:
http://howto.globalvicinity.com/gv_w...i=45&co=1&vi=1
http://homepage.mac.com/carldavis/intake.html

 

I ground it and there is plenty of room. Quarter inch at least.

 

Well, how have you been testing for vacuum leaks? Carb cleaner trick? If so, I'm assuming you've been propping the throttle open somehow to keep it from stalling, while spraying around the intake. I know you said you don't think it has any vacuum leaks, but that's most likely it. Refusing to idle is almost always a vac leak.

Did you keep the S4 LIM & grind/re-drill the S5 UIM to fit? Or did you attach an S5 LIM instead? Brand new gaskets on everything too, right?