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1992 mazda mx-3 with K8-ZE. OBD 1.

So, I am having troubles with my idle. I dont understand the corolation between the TPS, idle air screw, and the mini screw by the butterfly valve (the one u use an allan key and 8mm wrench to adjust). So, i've been messing with my car for days now. Sometimes I get it where it idle's at:
- 700rpm in neutral, but 1700rpm in gear.
- 600 rpm rough idle, 900 rpm in gear.
-1100 rpm idle, 1800 in gear.
-almost dead, to 1200 rpm idle, 1800 in gear.

So, i have read all the google,s i can possibly read and tried many combinations, getting the ECU to learn then and it never works out. Its great when i'm done and i've pulled the pin from 10 and GRND but after driving for 5 mins, it all messed up.

How do i correlate the TPS, and the screw by the butterfly valve correctly cause i now know i shouldn't have touched them but i did an engine swap. I get the idea behind adjusting the idle air screw with a Phillips. What i would like is

idle at 700rpm in neutral, and when in gear, 1000rpm, if this makes any sense.

Thx guys.

i know that when adjusting the TPS, you turn it until the fant goes on and tighten it just before that right......

how to set tps

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The little allen screw is the throttle stop. It's just there to prevent the butterfly from slamming closed against the throttle body. back it off, close the throttle and then screw the stop in until it contacts the throttle linkage and moves it just slightly. The butterfly should still be fully closed, but resting on the stop not the housing of the TB.

Then adjust your throttle cable so that it is slightly loose. You should be able to deflect the exposed part of the cable about 1/2-3/4" without affecting the idle. Any tighter than that and it will prevent the throttle from closing fully.

Do that first...then adjust the TPS using feeler gauges and a multi meter, then adjust the idle.

is it bad if the engine idle goes up when in gear??
Mine does that too (though much less dramatically) - in neutral, it idles at around 500rpm, but if I press on the clutch/put it in gear, idle goes up to about 700rpm... I assumed this was a feature to make the car easier to not stall when pulling away, but use less fuel when stopped at the lights, etc... is this ok if the car does this??

thanks for the help guys. I did the procedure twice and got it right on. It nice having it smooth again. I dont know why I couldnt find the posts for this but what ever.

I actually dont know why mx-3 GS's do the idle thing. My corolla gts (4AGE) never did it. Lol, i sold the corolla becuase it had rust my pocket couldnt handle by the way. mx-3 v6 are great though. I love em so, i swapped a k8-ze in to get a fresh motor.

thx again guys.

yes the rpms should raise a bit when putting the car in gear. in my case my car idles at 650 and goes to 1000 when in gear with the clutch pressed in.

if you start having problems again mike you can try running with the iac unplugged. my car sometimes doesnt want to drop to idle when at lights and hovers around 1000rpm. i dont have any vac leaks and i havnt figured out whats causing the problem. ive read somewhere that the iac valve can give problems and the car will run fine with it disaled. i havnt tried it yet but might be worth a shot.

There is a neutral switch on the manual trans that tells the ECU when it is in Neutral... could you guess that There is another very similar switch on the trans that is for reverse. (only used so turn the reverse lights on that I know of).
So that is how the cars knows to idle up. It increases the idle just to make taking off a tad more smooth and less rpm at idle to save gas and emissions.

Ok, cool... I thought it seemed fairly normal-ish, but this post freaked me out a little - I thought maybe something on my car was on its way out!
Thanks guys for your help

For the record...my idle does not change when I put the transmission in gear. When I think back over all the cars I've ever owned I can't say that I recall this ever being the case. In order for the ECU to sense that the tranny is in gear there would have to be a wire from that sensor going to the ECU. AFAIK the neutral and reverse switches are just switches. The neutral switch is normally open and locks out the ignition system when the clutch is not disengaged and the reverse switch just turns the reverse lights on.

I would need to see evidence of a ECU input from the neutral switch to believe that the symptoms you're describing are not related to a mechanical phenomenon.

wytbishop wrote:For the record...my idle does not change when I put the transmission in gear. When I think back over all the cars I've ever owned I can't say that I recall this ever being the case. In order for the ECU to sense that the tranny is in gear there would have to be a wire from that sensor going to the ECU. AFAIK the neutral and reverse switches are just switches. The neutral switch is normally open and locks out the ignition system when the clutch is not disengaged and the reverse switch just turns the reverse lights on.

I would need to see evidence of a ECU input from the neutral switch to believe that the symptoms you're describing are not related to a mechanical phenomenon.

I have no evidence, but I've noticed a consistent ~100-150 RPM increase when putting my car in gear, it was similar on the other 3 MX-3s I've driven. Granted, mine has been weird since my idle issues last month. I'll be using ALL the ideas in this thread today, as the weather is amazing.

Does the idle change when you putt he tranny in gear or just when you depress the clutch?

When the clutch pedal is out (i.e. the clutch is engaged) the engine is driving the input shaft of the tranny. When you depress the clutch pedal (i.e. disengage the clutch) the crankshaft and input shaft are disconnected putting less load on the engine and probably explaining why your idle goes up a little.

The fact that my tranny doesn't do this, and none that I have ever had did to my recollection, suggests that maybe you have some excess drag in your transmission...but I'm inclined to think that it's nothing to even worry about.

wytbishop wrote:Does the idle change when you putt he tranny in gear or just when you depress the clutch?

When the clutch pedal is out (i.e. the clutch is engaged) the engine is driving the input shaft of the tranny. When you depress the clutch pedal (i.e. disengage the clutch) the crankshaft and input shaft are disconnected putting less load on the engine and probably explaining why your idle goes up a little.

The fact that my tranny doesn't do this, and none that I have ever had did to my recollection, suggests that maybe you have some excess drag in your transmission...but I'm inclined to think that it's nothing to even worry about.

My mistake for not being specific, that is without releasing the clutch; The idle changed between ~100-150 RPMs for my car, and roughly the same for the other 3. 1 was a 4 banger, although I don't know how helpful that information is.

Right so when you push the clutch pedal to the floor (disengage) the idle goes up. When you release the clutch (engage) with the tranny in gear you go forward so I assumed you meant the idle changes with the clutch depressed and sitting in gear. But if, as I suspect, this has nothing to do with being in or out of gear it's just the drag in the tranny that's slowing your engine down slightly when the clutch is not depressed.

You follow me?

I'll try again.

When the clutch is IN, without ever being released in the process I am describing; The RPMs change when the car is put in gear.

A good example would be stopped at a red light:

You see lights perpendicular to yours go yellow.

You push in the clutch, and put the car in first.

The RPMs go up.