My car:

1990 RX-7 GXL
Auto
92,000 miles on body
27,000 on motor



My issue:

Right before storing my car last winter I was having some odd idle issues, but the car still ran for the most part so I stored it with the intention of getting it fixed in the spring.

Well, spring is here! I just got the car painted (the picture shows what it used to look like) and am still having the same issues. I just changed the oil, oil filter, and spark plugs today. Basically that car will drive fine but when you let off of the gas in park it dips to 200RPM then brings itself slowly back up to 600RPM where it stays. Like I said, it drives fine if you want it to and doesn't shut off. The engine temp is right in the middle where it should be.

I also noticed some steam/smoke coming from the intake manifold area closest to the driver. I touched the AC lines and they were HOT (not sure if this is typical or not). I noticed when I turn the AC or heater on the idle gets really crazy (and by that I mean the idle dips again from 600RPM to 200RPM).

Any ideas? I'll try and keep the thread updates as I try different things.

 

check TPS... although it's less of a problem on s5 cars

search BAC valve cleaning

 

Cool, thanks for the tips. Anything else I should look at while I'm looking?

 

It could also be a small vacuum leak, or leak before the throttle plates. Intake duct leaks are great for making your engine idle rough. And of course, check the TPS, as mentioned

In the mean time, you can adjust the overall idle speed up with the adjustment screw on top of the throttle body. Make sure the initial set coupler is set prior to adjusting.

 

Sounds like the bac valve for sure. It controls idle when certain electronics and such turn on and off to keep your idle stable.

 

Where abouts it the BAC located? I've got a service manual but it's not where my car or myself is

 

It's on your upper intake, should have vacuum and coolant lines running into it.

I think fc3s-pro.com or aaroncake.net has a write up on it

Exact location I'm unsure of on s5

 

This is from an S4 turbo but it should be pretty similar, look on your UIM for something with coolant lines, vacuum lines, and a plug.

 

I found it an cleaned it. My idle is now adjusted and is consistent, but is low. Where is the screw for adjustment?

It's idling at 400RPM right now. Where does it need to be at?

 

There should be a screw on the side of the BAC to adjust the idle. I'm not sure about the autos, I keep mine about 750.

 

I thought you are supposed to jumper a wire before adjusting idle?

 

Any truth to the above?

 

Yes, you need to jumper the initial set connector, or at least on the s4's you do. The idle set procedure is in the fuel and emissions control section of the FSM. Don't go fiddling with the idle until you read through the entire procedure and understand it, otherwise things will get worse before they get better.

 

It's not on the BAC valve on NA models. That's just a turbo thing.

 

Shorting the initial set connector just stops the BAC valve from working - so when you adjust idle, you are setting the base idle speed. You could achieve the same result by unplugging the BAC connector as well. I just make sure all electrical loads are off when I adjust it.