SN95 Auxiliary Switch Wiring

[Terrorist 5.0]

Hello everyone, in my next step on improving the car before it is relegated to daily driver duty, I need to wire in an auxiliary switch. I put out a post on here a couple months ago regarding what I am attempting. I am trying to manually control the IAC. The IAC on these cars are PWM actuated. However, if you give it straight up ground, it will remain 100% open. Combine that with a restrictor plate, and you have a high idle switch. I’m only looking to increase it 100-200 RPM, reason being, with my IAC disconnected to prevent the rev hang that these cars are known for, I have to pedal it for a couple seconds. With a high idle, I will not need to.

Secondly, with my lighter weight flywheel, the RPMs will drop fast when going to shift. This modification will slow it down, almost emulating a heavier flywheel, for daily driving comfort while shifting.

Anyway, I wired up a mock setup today to test it and it worked flawlessly. I cut the ground wire and attached a two prong switch, and removed the closest throttle body bolt, and attached the connection there. I did this to make sure it would work before going any further.

My only issue is I want to wire the system up so I can activate it from the driver seat. I have never wired car accessories before, but am decent at wiring. I just want to know if I can route the switch directly, or if I should use a relay for something relatively small. Also, where in the firewall can I route the wires through?

 

[ttocs]

The only time I had problems with revs hanging was when I used a cheap pro products tb. When I swapped to an edelbrock it went away.

So instead of having high revs when you shift, you just want it to idle higher?

 

[96blak54]

If anyone here can answer these questions, ttocs would be the person!
I like your idea tho! Being able to control idle at random is a neat idea to me. There are many vehicles that people modify and dont easily have a way to tune or their platform does not have much aftermarket support. A simple fix like this switch is a good idea.

 

[ttocs]

I am not sure how this will help. the revs hang because the IAC is open too far already and normally they are not wide open. You can adjust how far open it is and how slow it closes to return to idle in the tune and putting different components on the motor require this to make them work properly.

 

[Terrorist 5.0]

The only time I had problems with revs hanging was when I used a cheap pro products tb. When I swapped to an edelbrock it went away.

So instead of having high revs when you shift, you just want it to idle higher?

No, I believe you commented this on my last post regarding this. IIRC you have a fox body. SN95s have the IAC stay open during shifts to burn off excess fuel. It’s an emissions thing. I’m trying to accomplish an ever so slightly higher idle to slow down the rapid decline in RPMs when I shift, which will be worse with my lightweight flywheel. Also, I can start the car in the morning without having to pedal it.

 

[ttocs]

The IAC is programmed to stay open a certain %(I think mine is around %35 but it has been a while) after you take your foot off the pedal and then slowly closes back down close to 0(depending on temp/pressure) to the idle point. If you do what you say you want I would think that your hanging idle will never go down while shifting and probably even go up even higher than it is now.

 

[Terrorist 5.0]

The IAC is programmed to stay open a certain %(I think mine is around %35 but it has been a while) after you take your foot off the pedal and then slowly closes back down close to 0(depending on temp/pressure) to the idle point. If you do what you say you want I would think that your hanging idle will never go down while shifting and probably even go up even higher than it is now.

If I just rig up a switch now, yes. The car will IDLE AT 2700 RPM. Insanely high. I plan to put a restrictive plate, to lower the RPMs. Right now I idle at 800 RPM. I’m planning to get it to idle at 900-1000 RPM while activated, just barely above idle. It may not seem like much, but it will make a significant difference.

 

[Terrorist 5.0]

Was thinking more about it today, and realized that there should be no worries about shorts, as a short to ground on the ground side would just make the IAC hang open. No sparks, and no melting wires as long as they are adequately sized. I bought 14 gauge wire, and it looks a little thicker than what’s on there so I should be good to go. All I need now is somewhere in the firewall to get it through… I’m going to start drilling holes soon if nobody knows lol

 

[ttocs]

look where the stock wires go through the firewall and there is a large grommet around it that you can poke a hole in and pass a wire through. I am still not sure this will help, I assume there are no tuners nearby or is it the budget?

 

[Terrorist 5.0]

look where the stock wires go through the firewall and there is a large grommet around it that you can poke a hole in and pass a wire through. I am still not sure this will help, I assume there are no tuners nearby or is it the budget?

Sweet, I will refrain from drilling for now. I can record a before and after if you like, I think I may be able to sway your mind on whether it works or not. It’s more of a comfort thing in all honesty.

 

[duh09]

So your train of thought it being in manual control of the IAC at 0% or 100% is better than letting the computer control it across the range?

 

[Terrorist 5.0]

So your train of thought it being in manual control of the IAC at 0% or 100% is better than letting the computer control it across the range?

No. Ideally the IAC would function as normal, except it would not hang open during shifts. This requires computer tuning. Seeing as my car is stock and could use many other things before a computer tune, this is easier and quicker. I have daily driven this car without an IAC for months with no ill effects. I have the idle bleed screw turned up a little to compensate. I would recommend for people to try it out just to see what it’s like. It’s free, after all. Also, while the IAC will be at 100%, I am going to put a plate in to restrict airflow so it only raises the RPM by about 100, so a very small hole to allow just a little bit of air. Just a little RPM can make a big difference.

 

[Terrorist 5.0]

look where the stock wires go through the firewall and there is a large grommet around it that you can poke a hole in and pass a wire through. I am still not sure this will help, I assume there are no tuners nearby or is it the budget?

Just wanna say that was a very good call. I found the grommet where the wires passed through and made a small hole. Worked perfectly.