Idle Surge PFC bad TPS?
 

Hey guys, just picked up a 92 RHD FD which came with a bunch of mods which includes:

Greddy FMIC
Compression tube
BOV
HKS downpipes
HKS intakes
Mid pipe
Koyo Rad
PowerFc w/Commander (basemap)

and a bunch of other small stuff, previous owner also did the rats nest simplification, aswell as these deletes: air pump, idle air control, air pump control, accelerated warm up, dual throttle control, throttle body coolant bypass.

The car seems to have an idle surge once it is warmed up, I tried resetting the PFC and doing the idle learn process over with the screw under the throttle body out 1/2 turn but its still does it. Did some searching online and was informed to test the voltages on the TPS i could only get the narrow range within spec to .75 while the full range was .38 both in the closed throttle position. Could this be a bad TPS? Any insight is greatly appreciated.

I don't know about the TPS off-hand. Could be. If you haven't already, download a copy of the Factory Service Manual from the FAQ stickys at the top of this section. Loping/hunting idle after warm-up can also be from a vacuum leak.

Be very careful with a midpipe regardless of tune with the stock twin turbos. The wastegate is small and too little back-pressure can lead to boost creep...which can cost you an engine. Porting the wastegate can alleviate that, but requires pulling the turbos since it's internal. Usually returning some back-pressure in the form of a cat, even a hi-flow cat, is preferred.
You also need to monitor engine temps, especially with that FMIC. The stock gauge is useless so be sure to use the PFC commander or get an aftermarket gauge.

Typically if the TPS is good and the powerfc map is smoothed out, the surge is coming from an incorrect position of the throttle stop for idle.

on top of the throttle body there is a screw that holds the throttle slightly open at rest. If the throttle is open too much and the setting in the powerfc is too low the powerfc is trying to fight against the throttle set screw position and you get a throttle surge up and down.

you need to find the correct position of the throttle set screw where the powerfc can idle smoothly. small incremental changes when you change the set screw as it might take a little time for the powerfc to learn the new position.

http://s85.photobucket.com/user/choc...crews.jpg.html

#1 in this photo.

downloading it now thanks. Forgot to mention in the post that the car does have aftermarket water and oil temp gauges along with an Air/fuel ratio and a boost gauge.

Good to know about the wastegate as this is my first turbo car so its all new to me.

I believe that screw is just barely touching arm that its supposed to (previous owner). So after adjusting that screw incrementally do I have to do the idle learn process over? at this point im sure my neighbors hate me from the exhuast fumes and sound.

adjust it a little bit and see if it helps.

either the idle is too low and the powerfc is trying to raise it but cannot maintain it, or the throttle plates are open too much and the powerfc is trying to bring the idle down but cannot hold it down.

You can check the tps voltage in the pfc to see if it's in spec. I just had the same surging idle when warm happen to me. It turned out that the secondary butterflies in the tb weren't fully closing after acceleration due to oil and gunk build up. Cleaning them and pushing them shut fixed the surging idle issue for me.