Chris Ng

Well.. here's a puzzler for you guys, since I'm starting to realize that more heads are better then one..

88 T2 -
No ACV
No EGR
All solenoids removed (expect for FP and twin scroll)
Air bypass valve removed (The one on top of the manifold by the intercooler)
ASV Is still connected
BAC is still connected
double throttle plates + thermowax removed

okay.. Now the question.. on my previous 87 T2, with the same emissions setup, I had always been able to increase my idle by adjusting the idle set screw by the throttle cable linkages..
However, ever since I have had this 10AE (even when it was 100% stock) I've encountered a problem I can't seem to solve..
If I adjust the idle set screw even by the tiniest ammount to increase idle a tad, the idle will begin to "stick" .. what I mean by this is, once you have the idle set to the level you want, if you rev the motor, the idle will start to come down and then stick at about 1500rpm.. .The only way to brin idle down to the set idle is to increase engine load.. ie: Turning on the AC will drop the idle down to where it was set.. but the moment you rev the motor again, it sticks at 1500 rpm again...

So.. Let's disconnect everything that mazda tells you that has an effect on the idle circuit... ASV is disconnected along with the BAC valve ... Try setting idle again.. nope.. the idle still sticks at 1500 rpm...

Now I'm wondering.. what the heck is left in the idle circuit that can cause the idle to stick like that??

I have found that the clutch switch (There are 2 of them, I'm speaking of the one closest to the driver, not the firewall) and the neutral switch in the gearbox both have an effect on idle as well... If you disconnect the clutch switch and leave the neutral switch connected Idle will stick unless you place the car in gear.. If you disconnect the neutral switch and leave the clutch switch connected, idle will stick until you depress the clutch...
Disconnecting both the switches will allow idle not to stick, however it also causes the car to drop idle to near stall before coming back up to set idle level ...Once again, it's intresting that even with all the other emissions devices removed, the clutch switches can still cause a change in idle somehow.. I just have no idea where it's possibly controlling it from?

Keith

Hey Chris. Irv here. Just a thought, what may be happening here is due to a confused ECU. You will see in a lot of posts that this kind of wierdness is often related to misadjusted TPS. Well, if you use this set screw to adjust the idle, you will change the TPS adjustment. It may be changing enough to no longer realize you are at idle. The easiest solution imho is to put the screw back to its original setting, and do the idle adjustment via the screw built into the BAC. If you cannot get sufficient increase in idle by this method, then increase the idle via that screw by the throttle plates, and readjust the TPS to reflect this new point as idle, then you should be in range to increase idle via the BAC. Hope this helps!

Irv, Keith's dad

Six Rotors

iTrader: (17)

There is also another possibility--you will notice that there is hex head screw on the end of the BAC
(the smaller one,on the end where the electrical connector fits).This screw adjusts the stroke of the BAC.I did some experiments a couple of years ago and found that a practical range of 600 rpm of adjustment to be gained.This without affecting the setting of the throttle valves(and the TPS)

HAILERS

I gotta admit I've seen reference to these two switches on this site and more or less dismissed them having any relationship to the idle. Wrong. I do not know the exact relationship but I just opened the fsm on line on page 4b-6 and I'm looking at the component description of the control unit and right there, number nine, says in-gear condition(neutral switch and clutch switch). Usually I would think they were for a car with a automatic or cruise control, but this post sheds new lite. At work now but this weekend I'm gonna play with both switches and see how they affect(effect?) my idle. Bottom line to the question is I DUNNO. Right there is where I have a problem with this fsm. I need some manual that tells me how things work and the fsm ain't cutting it. Its like the oil injectors. No real description, although Six Rotors seems to have manual of a different sort. The fsm is ok, but lacking. Especially since it cost me 80 bucks.

Chris Ng

Hailers: I was quite surprised as well to find that both the clutch and neutral switchs had some effect on the idle system.. although disconnecting the 2 won't make your idle any worse or better.. it certianly does play a role in how the car returns to idle after coming off throttle...I have the same problem with the FSM and sometimes find it no better help then a haynes manual.. although there are some better descriptions of things here and there, there are still gapeing holes in explaining what does what..

Let me know your findings

Sixport: I was always under the impressino that the hex screw on the end of the BAC was adjustable on only the NA BAC's and that T2's couldn't be adjsuted the same way.. having said that.. I have tried loosening the screw once, but found that it was in there nice and tight so I stopped playing with it in fears of breaking the plastic end cap..

Irv: Yup.. gotcha, I've always re-adjusted the TPS whenever playing with the idle set screw.. this didn't solve the situation though

HAILERS

Curious, was this only happening when the engine was not fully warmed up???

Felix Wankel

This may not be relevant, but I adjust my idle the redneck way by tightening up the throttle cable.

Scott 89t2

if it's idling at 1500 rpm it could be something with the fast idle cam sticking.

asherwood

After cleaning the TB the idle shot up to 2k and stayed there!

I adjusted it down by using the air bypass screw and now it seems to have trouble starting when cold and the idle usually hangs in at about 1200 and rarely comes down to 750rpm. And the gas milage seem really bad now...

Does anybody know how to set the air bypass back to factory (like 3 full turns from closed etc.)?

Thanks for any assistance...

hypntyz7

I once had an NA do the same thing. I tried all the normal ways to lower idle, but it stayed around 1500. Turns out some fool had adjusted the dashpot in way too far. SOmething else to check for...on a t2, its easy, when having the upper intake off, to bend the tab that sits behind the alternator, as part of the vacuum spider, so that it interferes slightly with the throttle linkage and OMP rod, which can also hold the throttle open. Check for *physical* restrictions to the throttle closing fully.

Good luck and let us know what you find!