I know wrong forum for the car. I don't really know where else to turn to. If there's any help out there please let me know.

I know I have not posted in RX7 boards for 17 years. I took a hiatus from sportscars in 2012 for about 10 years. Jumped back into a Toyota MR2 in 2022, and now I have TWO of them.

One car is a 2.3l 5SGTE Stroker Big Turbo motor built a long while ago, and it's got an Apexi PowerFC on it. Being a stroker I know it's going to be rougher starting and idle, but none-the-less I'm trying what I can before I ditch this PFC for a new LinkECU.

The car:
1993 Toyota MR2 Turbo
Highly modified 2.3l stroker 5SGTE(3SGTE) engine w big turbo, uprated injectors, a TON of goodies, etc. Running MAP (Ditched the MAF).
IAC valve is a 3-wire, two coil push/pull rotary style.
Apexi PowerFC running v1.62 Firmware.
FC commander
FC Hako

Once warm, the engine runs great! The car is wicked fast and works pretty well a few times a year going to car shows.

The main issue is idle control. COLD STARTS really suck BAD. I have to feather the throttle until the engine gets to mostly full temperature. Once warm the engine idles really high, like 1700rpm. I tried playing with all the idle settings in FCEdit AND Copilot(May only be for Toyota) to no avail I cannot get the idle down. I thought the IAC might be getting controlled backwards or maybe not at all. 3-wire/2-coil IACs are normally half open with no power, fully open one way, and then mostly closed the other way. Wire 1 & 3 are coils and Wire 2 is +12vDC. I cannot find ANY functions on software OR commander having to do with Idle control, PWM, Duty, or otherwise; so I don't even know if the PFC is doing anything at all to the IAC.

I've tried resetting TPS, raising idle at the stop, plugging the IAC, clamping the air line, and several other things. It seems like the PFC just isn't doing anything to the IAC.

I brought up ChatGPT and eventually AI found that the APexi PFC may not be able to control push-pull/rotary style 3-wire IACs but I don't know where AI found that one out.

I ended up disabling the IAC and plugging the line to the intake, then propping the throttle to 1200rpm idle via stop screw. COLD starts still need to be feathered for 1~3 minutes! After that the engine runs fine.

I thought maybe I need a 2-wire Bosch IAC. Would the PFC control that???


Thank you any PFC experts.

 

Your issue may not be tune related. Try doing a cold compression test and seeing what the numbers are. Also verify there no compromises in sealing from the throttle body back.

If it is tune related, your iac strategies sound correct. I can say the pfc can control cold idle perfectly on a stock to heavily modified fd with no iac present. No throttle input needed.

I imagine you're not using pump gas with your set up but it may be worth checking your afr. You may just have a situation where its dumping too much or not enough fuel for the cold start. In fc edit there is a table for this. You can also adjust the load range at which it becomes relevant. It may be worth fidgeting with that. Try making large changes in either direction to see how it responds.

make sure the low load value is where you actually idle for maximum effectiveness. With your set up, you should have a pretty high base idle so i wouldnt make the effort to chase an iac solution. Once the actual fix is found, I don't think you'll need it. For the sake of troubleshooting, I would suggest leaving it out of the equation just to keep things simple.

 

hi, i have questions! is it a PFC for the 3SGTE? shouldn't it be able to control the stock idle framus, or is the US one different than the Japanese one?
with the Rx7 the IAC can only raise the idle (let more air in), is the Toyoter one the same? with the Rx7 you'd set the idle speed a little low, and then the ISC/IAC/BAC adds air and raises the idle.