FD UIM on S5 TII questions (not TPS wiring or installing)
 

I recently purchased an '86 Sport with a JDM S5 TII swap and a FD UIM swap without a spacer. The TPS wasn't talking to the JDM ECU despite having the FD connector. The wiring was incorrect and I've found other threads on how to wire them, so that isn't my question. However, my questions pertain to the FD UIM itself since I'm not familiar with them.

First, there is a small white two-prong connector underneath the UIM. One of the wires is green (note: I forget the exact colors of both wires; I can get them tomorrow if need be). It is in the same pigtail as the TPS wiring. I'm stumped as to what it is. I have looked at the 94 FSM and wiring diagram and the closest I could figure was a heat hazard connector. What is this connector for?

Second, I am planning to Megasquirt this car at some point. Nearly all FC Megasquirt threads/articles say I need a BAC valve to control the idle. There is no mounting point on the FD UIM as there is on the S5 UIM. Would it be possible for a machine shop to fab up a bracket and weld it to the side of the FD UIM without doing any damage to it?

post a pic of the connector you are talking about. It could be the IAT sensor on the primary runner (it's in the TB elbow on the FC), or it could be the AWS solenoid if it's a USDM FD intake manifold.

There is a BAC valve on the FD. It's on the back and is usually referred to as the ISC valve (Idle Speed Control). If you need to set it up in the Megasquirt, it runs at 244hz frequency according to the FD training manual. The previous owner probably blocked it off. It looks the IACV on a 5.0 Ford pushrod motor. Instead of an external hose feeding it like on the 2nd gen, it controls air fed to it through a big hole inside the FD TB bore. You'll see what I mean if you look inside the FD TB.

https://www.rx7club.com/attachment.p...1&d=1282694128

https://www.rx7club.com/attachment.p...1&d=1282694128

https://www.rx7club.com/attachment.p...1&d=1282694128

Thanks for the photos. Now I'll know what I'm looking at.

I'll try to get pictures tomorrow. If it helps any to identify the connector, it plugs into two prongs that stick out from underneath the UIM on the runner closest to the firewall, just before it bends down towards the LIM.

The connector you are talking about it the IAT (intake Air Temperature) Sensor. I just replaced mine tonight (on my FD) with a faster response one and it is exactlly where you described...

Yes, the factory FC IAT sensor in the TB elbow is already an open element fast acting sensor. On the FD the factory IAT sensor is buffered and responds slowly, so people replace it with either a Triumph motorcycle sensor (stock ECU or Power FC) or a GM style sensor (Haltech etc).

Looks like I'll be shopping for an IAC valve.