Redtop

Bone stock 91 vert only has racing beat cat back exhaust and runs great but will not idle below 1400 rpm. Battery went bad from setting and replaced and that is when idle went wonky. Used to idle extremely smooth at 900 rpm, now can't get it below 1400 even though car runs and drives very well. Tried adjusting tps sensor to no avail. Any help would be appreciated! Thanks

RotaryRocket88

iTrader: (7)

Has the idle adjust screw been played with? It's the one on the top of the throttle body. Sticking thermowax could also cause the problem. There is a cam on the back of the TB that holds the primary plate open when cold.

Redtop

Tried the idle adjustment screw also to no avail. Have not tried the thermowax. Can it be adjusted or is it something that has to be replaced?

RotaryRocket88

iTrader: (7)

You can't adjust the thermowax, but the cam has an adjustment screw. I'd get a small mirror and find the cam on the back of the TB, then warm the car up and see if it disengages or not.

This is a picture of an upside-down S4 NA TB. Yours will be similar. Unfortunately since the NA models were an after-thought, Mazda didn't seem to consider how anyone would make adjustments of any of these screws. The thermowax piston retracts when warm, which allows the cam to disengage (move left. The primary plate shaft rotates the same direction until it hits the throttle stop screw. Idle should be ~1500 RPM cold, and ~750 RPM when fully warm. Adjusting the idle bypass screw can bring these values higher or lower.

Redtop

Thank you so much for the picture. Ill take a look at that and try some adjustments there. Thanks again, great pic!

87FCna

iTrader: (3)

Sorry to bring back old *** thread. But does the S4 tb picture you display. The same as a S5 tb? Im having cold start problems. Does the 3k start up. Rpms slowly go down the dies. Hold a idle when
Once warm temp but the idle is very low. An idea's??

satch

iTrader: (1)

After it goes to 3000 rpm what does it drop to soon after and how long does it take to drop down from that number for it to die?

87FCna

iTrader: (3)

1500 rpms right after about 15 sec of 3k cold start. Then it slowly dies. Ive gotta give a tiny gas. Then once warm, it will hold idle but very low

87FCna

iTrader: (3)

Pictures of an S5 Na Tb would help me alot

satch

iTrader: (1)

When warmed up and idling, how low is this idle speed?

87FCna

iTrader: (3)

https://www.youtube.com/watch?v=SbYj...e_gdata_player

Cold start

https://www.youtube.com/watch?v=_E7n...e_gdata_player

Warm temp idle

satch

iTrader: (1)

The BAC solenoid is supposed to keep the idle from dropping below 750 rpm. Since yours apparently is below that level you need to do some research related to the BAC. Make sure the plug is making a firm connection. If so then unplug it and place a ground to one of the BAC terminals and a 12 volt source to the other terminal and it should click. Do this repeatedly to make it click. I would gather that the solenoid will click since your car goes to the 3000 rpm start level as the BAC needs to be functiong properly to do this but make it click anyway. Also, check the voltage at the ECU pin (pin3Q Blue/Green wire) related to the BAC and measure this voltage while it idles when the engine is warmed. Should read about 9 volts when idling, 2 to 3 volts when starting, and less than 9 volts while idling but the A/C on.

87FCna

iTrader: (3)

Could you provide a picture of the S5 bac

satch

iTrader: (1)

Looks like the item in post #8. Located on the passenger side of the engine.


https://www.rx7club.com/2nd-generati...erence-671004/

87FCna

iTrader: (3)

after looking at the picture you provide, am i using a multimeter for the air intake temp sensor?

HyperDrachen

My 88 GTU started idling really rough, the alternator tested bad and upon replacing it it was alot better. This might have only been part of the issue though. Just throwing it out there

satch

iTrader: (1)

The BAC and the Air Intake Temp Sensor are two completely different items. You're confusing me here. The voltage at pin 3Q is done w/the miltimeter set to DC volts.

87FCna

iTrader: (3)

This the onlything similar to the S4 you showed me

87FCna

iTrader: (3)

87FCna

iTrader: (3)

87FCna

iTrader: (3)

With a/c on idle prefect....

satch

iTrader: (1)

Nope. Post #8 shows a sensor with a hose on each side and the sensor says 'Denso' towards the end just like in the pic.

satch

iTrader: (1)

So w/the A/C on the idle is at 750 rpm? W/the engine idling but the A/C not on or any other option pull the electrical plug off of the BAC and see if the idle changes any.

87FCna

iTrader: (3)

https://www.youtube.com/watch?v=BG3B...e_gdata_player

satch

iTrader: (1)

In the first video where the engine is idling the rpm appeared to be about 300 or so. In the last idling video provided the rpm appeared to be closer to 500 or so. On the very top of the engine there should be a screw which helps to adjust the idle speed. So w/the car idling pull the plug off of the BAC and then adjust the screw on top of the engine so that the rpm idle climbs to a more normal level and then replug the BAC and tell us if the idle speed improved or not.

Pic of Idle Adjust Screw is in post#5 pic #1 in the link provided earlier.