RX7BEAR

This doesnt happen alot just enough to **** ya off !!!! I am coming up on a red light or stop sign push in the clutch down shift or what ever. And blam sh estalls sometimes like the idle is to low . But it isnt . Also if the A/C is on it does it alot more. And the idle goes up and down very very strange. Anybody else have this problem ? I have an 87 GXL.

sunshine

iTrader: (3)

Something very similar happens to my car. For me, it seems like the additional load created by stepping on the brake pedal stalls the car, but it does not do it consistently. Hmmm, I set my TPS. So next I guess I will look for vacuum leaks.

forgot - I got a 91 n/a

jimmyv13

I have the same problem, and I'm still searching........

PraxRX7

does it sound strange or run strange normally or just at the lights? Try just shifting into neutral while cruising, then try the brake...if when you press the brake the car's idle drops you have a problem.

The car's idle is supposed to go up when the load on the electrical system increases, I can't remember the name of the mechanism responsible for keeping this under control....whats that called again....anyone?

sunshine

iTrader: (3)

Yup, it drops...sometimes it drops a little, sometimes it makes it stall. BTW, it may or may not be important, but I'm running a two amp system that draws a decent amount of power.

WestJaxVert

I believe it is the Bypass Air Control valve (BAC) that controls that. Mine does it with the A/C on but I have been too lazy to fix it.

Dan

DJChunter

Same problem with my 87 GXL also... all it was is a vac leak on the intake plenum.. only like a $5 fix.. the gasket is $5 though mazda and it took like 1 1/2 hour to fix... no problems now.. just givin ya my $.02, Dave

iluvrx7z

Same thing happens to me. It started after I had modded my car. Intake, dp and mp, I don't know whats causing it but its annoying. I would like to fix it.

Ryde _Or_Die

Ya it happened to me on my NA and my TII. Both were after I installed an intake. Both happened to be leaks in my intake connections. Check them. Use starter fluid if everything is good and tight and you still have problems.

sunshine

iTrader: (3)

Is that the same as the intake manifold??? The one that houses the 6th ports?

DJChunter

well kinda... there are 3 pieces to the intake manifold.. the upper(the TB bolts to it) the Plenum with the 4 runners(middle, bolts to base) and then the Base (houses the 5/6ports) the most common prone leak is at the plenum to base gasket... which is a bad vac leak.. i had to replace it twice but thats a long story.. you can take the upper and the plenum off together in 1 piece.. but leave the base on... any more ?'s on how to didable you car ask.. lata, Dave

iluvrx7z

I'll check the intake area for leaks when I get home from college. Thanks for the suggestion!

Dan

sunshine

iTrader: (3)

OK....as per the FSM - Upper peice = TB, Middle peice = Exten Manifold, Lower peice = Intake manifold. Is that correct? So I'm interested in the gasket between the Intake and exten manifold? That is where all the vacuum leaks occur?

RX7BEAR

Damn I hope that BAC isnt bad them things are very $$$$$$$$ and I would hate to get a new one. I have checked for intake leaks and vacume lines . Everything is fine there.

HAILERS

RX7BEAR.....Lot of personal predjudice in this statement, but I don't think bacs go bad as much as the signal from the ECU is lacking. See this topic and the subject of bacs at the bottom http://www.teamfc3s.org/info/articles/idle.html I'm predjudiced because I've never had a bac go wrong, but I have repaired a N332 ECU using the info in the aritcle, and that ECU now works like a champ. You ought to get a clue of the bac's condition by just taking the plug off it while the car idles and seeing if the idle drops a touch. That method does not work on cars that have their idle honked up to some 900 rpm idle level though. Just on normal cars that idle around 750. Another clue of if the bac is doing its job is this question: When you start your car on a cold day, does it rev to approx 3000 rpm for about 17 seconds?? The car should do this. Its a combination of the air bypass solenoid working in conjunction with the bac to produce that high idle for 17 seconds. No high idle for 17 seconds might mean the bac circuit has been disrupted.EDIT: There is one small caveat to that though. If the water temp sw at the bottom of your radiator has one or both wires off, the 3000 rpm for 17 seconds is disabled. Sooooool....

RX7BEAR

yeah it does that . cold it goes to almost 3000 then drops off after gettin warm. maybe I should look for a used ECU see if it helps with my 3800 hesitation too

jimmyv13

Hailers,
Got a few q's for ya. My car ides up to 3K initially maybe once out of every ten starts. So, which should I check first, my BAC or air bypass solenoid? I have access to both of these parts at a local shop, so getting the parts is not the problem. I also have a hunting idle problem, 700-850, that is probably in conjunction with this, right?

Thanks in advance.......

HAILERS

Nah. If it does indeed go to 3000 when cold, that means that the bac and ecu are working in harmony to some degree. I'd still put the car at idle and see what happens when the plug for the bac is removed. Idle should drop maybe a hundred or maybe two. Thats if the idle isn't honked up to some screwball speed over 750. If the car goes to about 3000 FOR ABOUT 17 SECONDS and then drops down to about 1100 and steadily drops down as the car warms, then the bac is probably not screwed up . It was just a hunch of mine. I figured the bac was not working and a quick way to see if it was responding was to see if it was doing the 3000 rpm bit. Sorry 'bout that.

RX7BEAR

hell to me any help with these cars is good help . They have so many resistors and solinoids I go crazy lookin under the hood. I get the parts guys at the only Mazda dealer we have here In cold *** Grand Rapids laughing their asses off when it comes to asking for parts . They know nothing about these cars !!!!!!!!!!!!

HAILERS

Oh JIMMYVV13.....have I got a deal for you. Just does it once every ten starts'? Been there, done that. A good starting place is to check to see if the neutral switch is outputing a good ground to the ECU. IF that ground is excessively high from the transmission to the ECU, then you will not get the 3000rpm start up at all. Now that I've put my foot in my mouth, the first thing to check, prior to the ground from the neutral sw, is to see if you have the two wires on the water temp switch, located on the bottom of your radiator, on good. Clean oil and crude off. If one or both wires are off that sw, then the 3000 rpm start up will not occur. One way to see if that switch on the radiator is worth a flip, is to take the acv discharge hose off, and while at idle, see if its discharging large amounts of air. Some small discharge of air is normal. But if you have large amounts of air coming out the water temp sw should be suspect. You could pull both bullet connectors off and jumper a piece of wire b/t them and start the car. It should go to 3000 rpm with the sw jumpered. If it does not, then its another thing, which might lead you to the neutral sw not putting out a good ground signal to the ECU. Happend on my turboii, 1987 car.

HAILERS

JIMMYVV.......Here is a simplified schematic where I put orange juice on the two items of concern. To check the neutral sw for a ground go to the large connector on the ecu. Far right one. Pull the plug off, and looking in the back of the connector, count from right to left. The letter *A* is the top right pin, the letter *B* is just below that. The letter *C* is the second pin on the top row counting from the right, and on and on until you come to the letter *G*. Put a meter on this pin and find a good ground for you neg lead. You should have less than one ohm in neutral. Now put it in any gear. The reading should be zip. Try going back and forth to make sure you don't have an intermittant ground above one ohm. Here'd the jpg:

HAILERS

JIMMYVV.....I went back and looked at your question again. I'd still look at the water temp sw and neutral sw, but I doubt the air bypass solenoid is giving you the fits. If I disconnect mine on my car, I still get a high rpm on startup, its just less than 3000rpm. More like 2400rpm. I also discount the bac unless there is a bad connection at the plug on the bac like a socket not seated properly. On the 86-87 there is a relay involved, but lets not get into that. I firmly believe its the water temp sw at the radiator or a corrupt ground at the neutral switch. Could be wrong. Certainly not the air bypass solenoid if you get nadda high rpm of anykind on startup.

jimmyv13

OK....

Fisrt thing, the neutral switch is disabled somehow. I'm not sure how, yet,( the car is still new to me), but I do not have to push the clutch in to start the car. I was unaware of the switch until I read a thread about it.

The water temp sw seems to be in good condition and both wires are connected and not corroded. I just swapped in a radiator and I checked the switch over carefully.

HAILERS

Jimmyvv.....the neutral switch is on the transmission itself. On the right hand side on a turbo and probably the same on a n/a. Its not connected to the pedal. Side of the transimission. I'd still go to the water temp sw on the radiator and jumper the two bullet connectors and start the car. Should go to 3000. If not I'd meter the neutral sw at the ECU. Pin 1G on a 87 N/A. To work around not having to check the ECU, I'd jumper the water temp sw, pull the acv relief hose off and with the engine at idle, make sure no air(large amounts) are exiting the relief port. Lots of air coming out, then I'd ohm out pin 1G on the ecu for a good ground when the stick is in neutral. While there, I'd also check out the ground at pin 1H for a ground when the two bullet connectors on the water temp sw are jumpered. A reason for checking the outlet flow on the acv, is that the relief diaphram in the acv is disabled when either the water temp sw is disabled or the ground from the neutral switch ON THE TRANSMISSION is kaput.

jimmyv13

Let me try to explain this back to you and see if I'm getting it.

Jumper the water temp sw. If it idles up to 3K, then I need a new water temp sw. If not, pull ACV relief hose to see quantity of air. If I have a large amount of air from the ACV, then neutral switch is bad. What if I have a small amount of air coming out of the ACV with the water temp sw jumpered?