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When my 1992 MX-3 GS idles, it idles around 650 RPM, but when i put it in gear with the clutch in, the rpm goes from 1250 to 650 continuously revving, i was wondering if this is just a faulty idle control valve or something else. thanks

Oh dude. This is infamous. We need a sticky that says "Why your engine is rev hunting."

The following is my understanding, and the theories behind it may be flawed.

First thing I'd check in this case is for vaccuum leaks. Most likely candidate; cracks along the 3" diameter flextube that goes from behind the airbox to the throttle body sensor. At the airbox is a Volume Air Flow sensor that tells the engine computer how much air the engine is getting, to help the computer calculate how much fuel to give to the engine. If air is getting in past the Volume Air Flow sensor, this calculation will not be accurate, and the air/fuel mix will lean out. The oxygen sensors in the exhaust stream will pick up on the fact that the engine is running lean and tell the computer to put more gas in the mix. The result is a constant rev-up, rev-down condition which you are describing. You can fix this by patching your intake tube, or by replacing it. While you're at it, you might as well replace it with a cold air intake, which will improve power minutely, but also look very nice and help the engine breathe better overall. While you're under the hood, check all visible hoses for cracks and make sure none are disconnected. This engine is extremely sensitive to vacuum leaks. If these steps resolve the problem, search the forum for information on how to set your Idle Air Control Valve. Do not mess with it until you have solved all vacuum leaks, and until you understand exactly how to set it, or you may run into more problems than you already have.

Good luck!

tehbrookzorz is right on the money.

Mine did the same thing,i patched the leak on the intake,problem solved!

ok ill try that, thanks guys

[quote="cbrzx"]tehbrookzorz is right on the money.

Mine did the same thing,i patched the leak on the intake,problem solved![/quote]

mine had a problem like that , but it turns out my throttle body was badly worn and letting air in even when it was completly closed , and my IAC wasent working right.

i had the same problem with my mx3 idle problem. one day i just unhooked my negative battery terminal for 10 minutes. rehooked the battery terminal and it bought my idle back up to 1 rpm instead of 750 been running like that since.

Hi , I have the exact same problem as the first post. It idles high in general , and when i push the clutch in and put it in gear, i get the revving described. (but i have to do both clutch and gear to make this happen)....

i do have a big tear in the accordion-like intake hose a year ago but i patched that...(this only fixed the very rough idling in neutral). I've re-patched so i don't think that's the problem.

My mechanic said it's the idle air intake control valve sensor....but that's a $600 part...!!!!!

any suggestions of direction?
92 mx3 v6

Ya, ive got a k8 iac and a ze iac. Make an offer!

Hey kevin, did your car idle high in neutral or just in gear, with clutch in??

Idles high in neutral. If i push in the clutch, the idle doesn't change. If I push the clutch in and put it in gear, then I get the up-and-down revving. The check engine light comes on sometimes after driving around. I suppose my mechanic ran it thru the computer and it came up with idle air control valve, but I'm hoping it's something cheaper....

Idles high in neutral. If i push in the clutch, the idle doesn't change. If I push the clutch in and put it in gear, then I get the up-and-down revving. The check engine light comes on sometimes after driving around. I suppose my mechanic ran it thru the computer and it came up with idle air control valve, but I'm hoping it's something cheaper....

k, mine only does that when clutch is in and in gear, so it is possible it is a vacuum leak for me, but mine idles fine otherwise, so i think we got similar but different problems :D

As far as the problem of it idling like that in gear, I'd say the Idle Air Control Valve is either open too much or not functioning properly. May be a vaccuum leak elsewhere. Still, make sure the vacuum leaks are all gone. A patched air intake tube can crack again, I've experienced it. Silicone doesn't always stay where you put it. Duct tape peels, etc.

I had the same problem, but repatched my intake (I really need a cold air intake), reset my IAC and it went away.

Thanks, is there a way to test the vacuum/leaks in a better way than eyeballing for holes...?

I had this problem and for those that are not do it them self types or just don't have the time to figure it out, I took mine to the Mazda dealer and they replaced my rad cap and readjusted the idle screw and $80.00 CAD I was out the door, and it is running perfect. Best $80.00 I have spent on the car thus far!!!