Craze8

1987 Turbo 2 stock intake manifold and intercooler. To set the idle you jump the set connector and adjust the screw on the BAC. I know the electrical part of the valve functions, tested with 12v and can get the valve to move back and forth. Yet no amount of turning of the screw will get the idle to adjust. Is there a way to test that part of the valve? Or is there a flow diagram I can get to check all the paths of air flow into and out of the valve?

Aaron Cake

iTrader: (1)

Pull the BAC off and clean it up with carb cleaner. They can get carboned up over time.

Most importantly is to determine if anything else is holding the idle. In the past, some hack job mechanic or owner could have tuned the hard idle stop screw on the throttle body to compensate for some other issue. So it is best to start from scratch and perform the FSM idle setting procedure. Also, the RPM has to be around idle speed because above 1000 RPM (I think, from memory) the ECU doesn't try to regulate with the BAC.

Craze8

Thanks Aaron, I will pull it off and give it a through cleaning. I know the electrical part works as I have had it off and tested that and cleaned that area. I will clean the two ports that come in and go out of it via the tube on the intercooler and the one off the charge pipes and see if I can get the BAC screw to free up.

Craze8

Thoroughly cleaned the BAC yesterday after work, idle is now adjustable via the BAC. Something else is hanging it though. Let it sit and idle up to temp it will hold a idle at 800rpms or there abouts, disconnect the set connector and the BAC jumps to life bringing the idle up over 1krpms, whenever it settles out, it then hovers around 1100rpms before it decides to settle back down to 800rpms. Does this coming to a stop at a stop light as well now, hover at 1100 and just about the time the light changes to green the idle slowly drops down to 800.

Spoke with the PO of the car, he had at one time adjusted the idle with the throttle stop. I'm attempting to find the closed throttle spec to get it corrected and go back at this again.

Craze8

Okay, got the throttle stop adjusted correctly, was still having the issue. Pulled the intercooler up and check everything all over again. Found my IAT at the throttle disconnected. I felt small at that point. We all have those moments, Reconnected IAT and everything worked perfectly right down to the idle AFR (12.5 to 13.8). Feeling fairly confident in now that the car was done. I turned it off and began cleaning up my work space at work.

About 30 minutes later I started the car and it was right back to square one with the idle that takes a while to come down to where its supposed to be and rich afr at idle (10s to low 11s). I wasn't amused. I am going to check codes tomorrow in the am (Hopefully its not freezing out). Whats the likely hood that the IAT at the throttle valve is my issue? Reading up on what the car acts like when the IAT is bad, it thinks the charge air is always 68* Which right now its definitely not that outside (Likely a high of 30* tomorrow)

Craze8

Wont' let me edit, misstyped. the Idle will hang at about 1200rpms but will eventually drop down to 800 rpms

SURGEY POOH!!!

iTrader: (1)

I have that too on my na and because I don't have a bac when I'm at a light I turn my steering wheel and it'll drop and it'll drop if I engine brake. I still don't know why it does it I've done everything possible. I would check the IAT but I don't have a resistor laying around to check the IAT but let me know if that solves your problem

Aaron Cake

iTrader: (1)

I'm betting the previous owner played with the variable resistor on the passenger shock tower. It adjusts the idle AFR. There is a specific procedure to set it in the FSM. Also make sure the cold start high idle thermowax is working correctly.

You will likely have to chase the idle while adjusting the variable resistor while chasing the idle. Of course make sure the initial set coupler is jumped during this whole procedure.

You are seeing these problems because you don't have the BAC. Reinstall it. Also make sure the ASV has not been removed.

Craze8

Checked codes this morning, no codes. I will go through and check the setting of the thermowax. Then work with the resistor. On a cold start it will idle at 2k rpms. I know the accelerated warm does not work. Car has never idled at 3k on a cold start. I will work through these things and check back in. Wont be till monday night though at this point.

Craze8

Okay, updating this. Thanks Aaron for the help so far. The idle no longer hangs, combo of the cold start throttle adjustment and tps needing readjusted afterwards. Inside at 70*f the best i could get out of idle afrs was 11.2 to 12.5. Pull it outside after washing it and the afrs are high 10.8 to 11.5 Still at abit of a loss on this unless the iat in the vane is telling it to be rich at 30* outside temps.

Craze8

Guess I stand corrected. After 20 minutes of driving the idle is once again hung at 1300 rpms. I can see this as being a love hate relationship here in the cold season. Have to wait once more to take another look at it to see whats hanging it.

Craze8

Looks like I may have misadjusted the cold start thermowax setup. Will have to get the coolant temp back to the correct temp and check adjustments

Aaron Cake

iTrader: (1)

Make sure the throttle body isn't sticking either. I've seen a lot of sticky throttle bodies on FCs lately and I'm not sure why. Probably people greasing them up when they shouldn't.

It can be a bit of a pain to get the cold start thermowax system adjusted properly. Unless it was messed with, no adjustment on the thermowax itself should be necessary. Only making sure the cam assembly still works correctly.

You also need to make absolutely sure there are no vacuum leaks.

Craze8

I know the plate assembly for the thermowax was sticky when i was trying to adjust it. Figure at this point I will pull the throttle neck and clean the plates. The only adjustment Ive done was adjusting the screw for the thermowax. I dont hear anymore vacuum leaks, still confused as to why its rich. Trying to lean it out with the set connector connected did nothing, checked the resistance specs on the resistor per the fsm and it checked. I will smoke it this weekend just to be sure theres no more leaks after the throttle

Craze8

On another note, if I lug the motor. IE, let it pull itself at idle rpms, the idle returns to where it should, but the afr is still wrong.

Craze8

Update on this, smoke tested the intake track this weekend on a warm engine, found a leak right after the afm, repaired with a new boot. Found a vacuum line loose, addressed that and added a zip tie to keep it in place. Removed intercooler and smoke tested the intake from the boot on the intercooler to the motor. Smoke rose from the middle of the engine. In the back under the intake. I didnt remove the upper and continue to test as I have to make something to smoke test from the lowwer back. This in mind, theres two vacuum lines down there, one goes to the lowwer manifold the other goes onto the motor for.fuel atomization if i remember correctly. The PO left the oil injectors in the motor and put rubber caps on top of them, i did see smoke rising from one of those caps. I will look into one of the block off kits for that situation. Other then injector orings, is there anything else under the upper that would leak?

Also, the cold start system is now properly adjusted. Still once warm it acts like something is hanging the idle, can almost hear the BAC or one of the other air valves activating if you try and cost down to idle. If you put in the clutch after the engine is warm it will hover at 1300 rpms. From a cold start and letting the motor idle on its own it will drop down to 750-800 rpms but the afr is still in the low 11s might jump to 12.5. Once warm and driving it goes back into the 10s and the high idle.

Craze8

Update on this once more. I installed the proper block offs for the the oil injectors, mades sure the tps was set to 1v at full operating temp and proceeded to adjust the idle. With the BAC screw backed almost all the way out and atempting to adjust the idle afr screw I succeeded in getting idle in a room at 70* to around 12.4-11.5 afr. I moved the car outside into the cold air and once again the idle once warm hangs, it sounds like one of the air valves is being activated and holding the idle between 1100-1300 rpms, car sits long enough and it will drop back down to where it should be, however the afrs are back down in the 10s. To kinda back myself on the idea that its an air valve holding open or being pulsed open, coming to a stop at a light or a stop sign, if you let the car come to a stop on its own and clutch at 700rpms, you feel and hear the sounds of a valve forcing air into the system and it causes the car to shake from between 1600rpms to just under 1000rpms.

Thanks again Aaron for all the help. I am going to open a thread in the second gen tech forum to see if anyone has any insight before I buy stand alone and monitor whats going on.

Aaron Cake

iTrader: (1)

If the car isn't warmed up, the BAC will try to regulate the idle higher.

If you have no emissions equipment, the AFRs will show around 11 - 12 at idle as the stock ECU idles the car quite rich. Air would normally be injected via the air pump into the exhaust ports to feed the cats.

Try disconnecting the ASV and air bypass valve to see if that effects the idle. If they do, something is weird as they aren't typically used at idle unless A/C or PS is creating a load.

Craze8

The car is up to operating temp by the gauge on the dash when this begins to happen. I will disconnect the ASV on my lunch tomorrow and drive it. If it continues I will then disconnect the BAC. The car has a manual rack, but I am not sure if it had power steering to start with. The AC has been deleted, though I will make sure the switch for it is off in the logic con.

AFRs- Makes sense, so nothing I can do with the stock ecu will get it to lean out any further. I know I need to go standalone, but I want to make sure all the bugs are gone from the car before I go there and compound something.

Craze8

Disconnected the BAC and drove the car. It was at base idle on cold start. Once at operating temp the car tried running at mid to low 10 afrs and idle was at about 600rpm. So, now the question is is what is the ecu seeing that its commanding the BAC on.

Craze8

I will reconnect the bac and disconect the asv and see if there is any difference. On the drive home

Craze8

So, reconnected the bac, disconected the air valve bolted to the back of the intake, out of my drive cycle it only hung once and that was at 1100 rpms. Reconected it and disconected the air valve ontop of the intake manifold that is fed off the intercooler. It wanted to hang at 1100 rpms more often but not constant. Thats my update, wish I could find a flow chart of why idle is kicked up so I could start eliminating parts of the system

Aaron Cake

iTrader: (1)

I do believe the FC training manual has the info about under which circumstances which valve is used to bring up the idle.

Foxed.ca - Mazda RX-7 Manuals

Craze8

So, from what I just read, It could be an issue with the sensor on the radiator? I will play with that (well whenever I make it back to work as we are mid blizzard right now) next

Aaron Cake

iTrader: (1)

Yes, could be the little switch at the bottom of the rad. Jump it with a piece of wire and see if that changes things.