I'm running a half-bridge 13bre with an AP Engineering PowerFC in a S5 T-II and for some inexplicable reason, it idles at 2500 when cold and increases to 3000 when fully warmed up. I've had the manifold off and checked for vacuum leaks meticulously, as well as checking by spraying carb cleaner around various parts of the manifold while the car is running. I'm 99% sure the car does not have a vacuum leak. The car has no form of electronic idle control, I'm running an FD throttle body and have the throttle stop screw backed so far out that it isn't even touching touching where it would contact the the throttles, the air bleed screw on the bottom of the TB is all the way closed, and the throttles are indeed closing all the way.

The car is currently untuned running BDC's 850/1680 HBP map. The injectors are all brand new. I recently had to change the CAS and had a "reputable" tuning shop set the base timing for me. The car is currently running pretty rich and I want to start tuning the cruise section of the map so I can start breaking in the new motor, but I cant really get started until I figure out why its idling so high.

 

what is the idle set at on the power FC?

 

1200. But like I said, the car has no IACV

 

If you don't have a vacuum leak in the intake system somewhere then it would seem like either a throttle plate is adjusted incorrectly allowing too much air in or perhaps the fast idle waxrod is not extending and closing the throttle plate as the engine warms up. Could the accelerator cable be too tight?

 

check this. I had it happen to me, and it was the last thing i thought it would be. Also, as strange as it sounds, check the screws in your TB. A friend of mine had one fall out in his SR20 and it caused him to have a high idle.

 

Sounds like the fast idle cam is up, holding the primary throttle plate open.

 

The primary throttle plate linkage should be resting against the throttle adjust screw. What is your VTA2 (narrow range signal) TPS voltage? It should be 1 volt or less assuming the TPS is on there right. Check under etc.-->sensor/sw check in the Commander.

Try this. Take the intercooler piping off the TB elbow. Stick your hand in front of the TB elbow, choking all the air off the TB. That should make the car stall--it's an old Honda trick. If it doesn't, you do indeed have a vacuum leak. And one of my favorite ways to check for vacuum leaks is to pressurize the intake tract.

 

The TB has the thermowax/fast idle cam removed and there is plenty of slack in the throttle cable. I'm going to try choking the car out with my hand on the intake elbow and see what it does. If that does indeed kill the car then I'll look to see if any TB screws fell out and report back. Thanks guys

 

^^^^ That is a good idea.

B

 

You can even pressurize the intake system with a air compressor thru the brake booster port. I used this when a TB wasn't closing all the way off causing the same problem.

3 Hours of troubleshooting until I found it

 

thread revival

I just today (yeah I know its been three months) tried choking out the car by covering the TB elbow with my hand and it died instantly. No sputtering or attempting to stay alive. Does this mean I should theoretically be vacuum leak free? I took off the TB and inspected the plates and linkages and they are all closing 100%. As far as I can tell, the ONLY way any air is getting to the motor is through this port on the TB. Why am I still idling over 2000?

 

It might be ok, although a pressure test would provide more information. The arrow points to the feed hole for the ISC/BAC valve. A small amount of air still gets through the throttle plates as well.

Put the car back together. With a completely cold engine, hook up a datalogit. Go into the monitor window and select "Advanced" and "Sensors" only. Begin logging. Start the car. Keep your foot off the gas. Let the engine sit there and warm up completely. Post the log. It might be too big, you'd have to link it or email it to me and anyone else who wants to see it.

 

Believe me, I wish I had a way to pressurize the intake but I don't have access to a compressor.

I may have to apply throttle to get the engine started, will the test still be relevant?

 

if you have to give it throttle, give it throttle. do you have the ISC/BAC valve hooked up?

 

negative - all forms of idle control are eliminated except the air bleed screw under the tb and the other screw on top

I ordered new intake manifold gaskets from mazdatrix. Once they arrive I'm going to make gaskets for my block off plates (guy who built the motor used silicone) put it back together and see what it does. If its still idling high I'll either push it off a cliff or post the results of the logs.

Thanks for the help ya'll.

 

pressure test for any kind of vacuum/boost leaks after you install the gaskets

 

old thread but did you find that your idle control valve leaks? because im havin this same issue and upon inspection it appears the valve is letting air bypass when unplugged