first of all, what exactly does it do?


With mine plugged in the revs shoot upto 3k when cold, then hunts from about 1500 to 2500.

With it unplugged it idles fine but to start the car you need to blip the throttle.

The car was mapped with the it unplugged. Is there a way to adjust the PFC with the idle control valve plugged in to sort it all out?

The car seems to start a lot easier with it plugged in.

Mine is a Jap car

 

I am in the process of reinstalling mine as I had it removed for some time. On a stock port, it was OK, but with my half bridge, it's a pain without it (or so I hope).

It's essentially a bypass valve. The PFC has a few settings that will control that valve. How well varies from car to car it seems.

IIRC, on the settings 1 page, in the Function Select section, #5, Idle-IG Cntrl needs to be checked. From there, in the Rev/Idle section, that should determine where your idle will be set.

Idle hunting is the M.O. for these things. Sometimes, after the PFC is initially setup with the ISC installed, it will hunt from a few minutes to a few days, maybe longer. It's kinda finicky.

This is of course assuming you have the DL and are using FC-Edit. I haven't used my commander in years so I can't say how to set that, if even possible, from just that.

 

Assuming operation is the same as on the Miata, the IAC valve is only active when 1) the engine coolant temperature sensor indicates a warm engine, 2) the Throttle Position Sensor indicates the throttle is closed, and 3) either the gearshift is in neutral or the clutch pedal is depressed. When it is active, the ECU uses a series of voltage pulses, duty-cycle controlled, to position the IAC valve opening by means of its solenoid current. It is properly set up by first connecting a jumper wire (or paper clip) between terminals "TEN" and "GND" of the Diagnostic Connector. This opens the ECU control loop. Then the Air Bypass Valve is adjusted so that the idle speed is the same for either jumper connected or disconnected, with all electrical loads (A/C, lights, stereo, etc) OFF. The ECU will then attempt to hold the idle at 720 - 750 rpm for all conditions of electrical load.

The unit that causes a 3000 rpm "idle" when cold is not the IAC valve, it is the AWS ("Accelerated Warmup System) valve. That works to let extra air into the intake manifold when coolant temperature is low, for a faster warmup (read "emissions control"). This valve has been removed and plugged by quite a few forum members (including myself).

 

it sounds like it's the aws valve then. Because with it plugged in the car starts fine. Goes to 3krpm. But once warm hunts for idle.

When unplugged I have to blip the throttle to get it to start. No 3k rpm warmup, and no hunting issue.

A couple of questions...

Why do I have to blip the throttle with it unplugged to get it to start? Also is there a way to sort the hunting when it is plugged in? I have apexi pfc and the previous owner said it was mapped with the valve unplugged, hence the hunting.

 

If i have my idle set for lets say 1400 rpm on the PFC, can i eliminate the IAC?

 

Jim rx7, no expert here on the stock system, and you have a PFC! But it might be worth your while to plug in the IAC connector and set the idle speed with "TEN" jumpered to "GND" in the Diagnostic Connector on a warm engine. Seems like the PFC should have been set up with the IAC connector engaged, too, but I know zero about the PFC's interaction with the IAC valve, sorry. You need input from Dave Geesaman or Dave Clark, or Mahjik, or another PFC expert here, IMHO.

Just looking at the IAC valve on the FD, it would seem that if there is no current into the solenoid (connector disconnected), the valve would be completely closed by return spring pressure. In that case, when cold, the only incoming air would be through the AWS valve, but when warm, and the AWS valve is closed, there would be only leakage air around the closed throttle butterflies getting in at idle. That would tend to kill your engine, I think.

 

J-spec cars don't have the accelerated warmup system first of all. That is on US spec cars to pass EPA cat warmup regulations. In fact, on US cars you are supposed to cut or de-pin the AWS wire when you install a PFC.

When plugged in and working correctly, the ISC opens fully to allow extra air in on a cold start. It is effectively blipping the throttle for you, without moving the throttle plates. That's why it's starting easier.

Why is it surging and/or idling high? A few things cause that. The first is too much air getting past the throttle plates. For whatever reason, the PFC usually needs the throttlebody adjusted for less idle air in order to maintain a stable idle. There are half a dozen screws that control idle air when cold and when hot, but usually adjusting just one or two of them is all that's necessary. The second thing that can cause problems with the ISC being plugged in is not following the idle learning procedure, which requires you to reset the Power FC and lose all your settings (if you don't save them to a laptop with a datalogit box). I have never heard of anyone setting the idle on a PFC using the FSM procedure (jumpering TEN). The third cause of a surging idle is purely a mapping issue: a mixture leaner than about 13-13.5:1 (if you have no smog pump) can cause surging, especially on hot start when a heatsoaked air temp sensor leans the mixture out further.

If you don't have a datalogit box you are going to have a lot of trouble getting it to idle very well with the ISC connected, mostly because you can't save maps and quickly make adjustments. You have to take the plunge into self tuning to get it right on your own, which means spending the money on a datalogit and spending the time needed to learn how the PFC works. My advice is: don't mess with it. It is possible to get it to idle smoothly with the ISC plugged in, similar to factory (It takes many hours to get just right), but if you try to do that it will run worse long before it runs better.

It's a good thing Mazda did away with that complicated mess and went with a drive-by-wire system on the Rx-8's. Their idle and emissions systems are MUCH more reliable than the FD's or the 2nd gen's (which are even more complicated and less reliable than the FD's).

 

So if I have it plugged in, once it starts to idle hunt, try to adjust the screw under the throttle body?

Possible resolve the situation?

I know roughly where the screw is. What direction to turn for less air?

Also, is it ok to do this with the elbow off? Ie no elbow, but the car running?

 

Clockwise on screw reduces bypass air. No reason to have the elbow on... except that even at idle the primary turbo spins a little, and might increase the bypass air slightly. Not much, though.

 

I'll give it a bash today. I assume if it's completley closed then the car will just stall??

 

There are a few good threads on the forum about fixing/setting idle, throttle body mechanical settings. I believe they are in the FAQ and in the Archive 3rd gen sub forum. Find them and read them.

Your surging is probably from bad throttle body hard settings so you're on the right track there.

I think wstrohm provided to most correct info on here. Search his old threads too for more idle info and adjusting threads.

 

Yes, if the primary and secondary throttles and the air bypass screw are completely closed, and the AWS valve is closed, and the IAC valve is closed (de-powered), the only air that can get in is from one (weird) factory hose between the Y-pipe and the injector locations, which supposedly improves vaporization of fuel, plus whatever leaks you might have, say, in the rat's nest or the LIM manifold gasket.

 

i was having the same problem(start around the 8th post)
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/3k-rpm-idle-825509/

 

All the units I found to replace the air idle control valve have a 2-prong connector off on an angle. I have a 4-prong connector that comes off the back of the unit. What gives?

 

Is that what it actually looks like or a stock photo? it should be 2 pin.

 

It's definably a yellow 4-prong and the connection is at the rear of the unit, not on elbow.

 

I second this...it is definitely a 4 pin connector.

Send ChrisLudwig a PM...if he doesn't have the connector in stock, he can point you in the right direction.

 

Hopefully someone sees this! Only way to get my Turbo FC rx7 started is by putting a screwdriver to hold the AFM open manually.. got a brand new AFM and the problem still occurs I just can’t seem to crack the issue and find out what’s going on. The car immediately stalls without the screwdriver holding it open and won’t start back until it’s put back… any help/suggestions would be appreciated thanks