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 idle drops low for a second when letting off throttle. 
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Joined: May 21 2009, 11:19 AM
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Post idle drops low for a second when letting off throttle.
I have a 94 mx3 with a 1.6 dohc motor and a manual trans
i have researched the hell out of this and it seems to be a common problem with a lot of different cars. WTF. so when the car is cold it is fine. when it gets to op temperature and the sensors start working i have this problem. the car idles just fine (however it seams a touch jumpy, but not much. you wouldnt notice unless you sat and listened to the motor. its not perfect). so when it is idling, if you rev the motor, when the car idles back down to below 2000 rpm (ish), it quickly drops to 300 400 rpms then back to 900 where it is supposed to be. happens every time. same when you are driving it. it drives just fine but if you let off the throttle, when it gets below 2000ish rpms, it jerks the car (like chokes it or something). not smooth at all. VERY jerky when you let off the gas. seems like something is messing with the idle air control valve or something. im really not sure. the iac looks fairly clean. i cleaned the maf sensor. replaced and readjusted the TPS. replaced the ecu. it throws no codes and if i unplug the tps it runs just fine but with the check engine light on. same if i unplug the maf sensor. it wont do it then but it runs like s--- when you try to drive it with the maf unplugged. no power at all. i unplugged the wires to the egr and it still does it. i dont know what the hell it could be or how to test for it. is it pos that the maf is bad but not sending codes to the ecu. plus i dont know how to test the maf on these cars. the books are all wrong and dont tell you how to do it. does anyone know how to test the maf on a dohc 1.6 mazda.


November 10 2011, 1:56 AM
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Post Re: idle drops low for a second when letting off throttle.
I think for the most parts its how our IAC works, and the time it takes to respond. Partly in the fuel-cut system.


My KL does it too, but it also idles like a drag car from the cams, so it all goes well with the "sounds like s--- but goes like stink" facade its got going on.

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November 10 2011, 9:59 AM
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Joined: May 21 2009, 11:19 AM
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Post Re: idle drops low for a second when letting off throttle.
yeah but it kills the car sometimes, like if im turning. and its not really drivable. it is constantly jerking the car back and forth when driving. it does it if you let of the throttle. once the tps sensor hits idle there is a second and then it cuts. really weird.


November 10 2011, 10:32 AM
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Post Re: idle drops low for a second when letting off throttle.
i had another one of the same exact cars i sold a while ago and it didnt do this so its something with this car. o and on a side note. if i have all the sensors plugged in when the car is running. if i push in the clutch, the car dies. CRAZY. does it every time. i unplugged the clutch pedal switch thing under the dash that sends the signal for when the clutch is pushed in and that solved the issue. how the hell could that do anything. seems like it should only go to a neutral safety switch and thats it. i unplugged it and the car still starts. wtf


November 10 2011, 10:35 AM
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Post Re: idle drops low for a second when letting off throttle.
seawulff wrote:
i had another one of the same exact cars i sold a while ago and it didnt do this so its something with this car. o and on a side note. if i have all the sensors plugged in when the car is running. if i push in the clutch, the car dies. CRAZY. does it every time. i unplugged the clutch pedal switch thing under the dash that sends the signal for when the clutch is pushed in and that solved the issue. how the hell could that do anything. seems like it should only go to a neutral safety switch and thats it. i unplugged it and the car still starts. wtf


Sounds like you have a wiring problem


November 10 2011, 11:53 AM
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Post Re: idle drops low for a second when letting off throttle.
yeah so i think i figured it out and this is weird. so there is a neutral safety switch AND a clutch pedal switch. somewhere along the line there is a short or something cause if i release the switch the problem went away. i checked the pin out diagram and both sensors/switches go to 1 wire and when activated send a ground signal to the ecu. so i clipped the wire from the ecu and ran it strait to ground. so far problem solved. turns out, from what i have seen so far, your neutral safety stuff REALLY screws with your car. weird. any thoughts?


November 21 2011, 1:53 PM
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Post Re: idle drops low for a second when letting off throttle.
update. ok so the problem is everytime i put an electrical draw on the system it messes everything up. so when the neutral safty switch turned on, it pulled on the motor, when the lights were on, it pulled even worse, if you had the heater and the lights on the car would idle up and down really bad......but if you unplug the idle air control valve is stopped this.....so when there is something that puts a draw of power on the motor ie heater or headlights, the computer has switches and sensors to read that and to compensate accordingly to try to maintain a decent idle.......heres the big kicker... so if i unplug the iac, then as i turn accessories on, my motor will get pulled on slowly drop down and almost die if you have a bunch of stuff running, BUT if i unplug the connector to the alternator, (not the power wire but the 2 wire plug) and have the iac unplugeed, then the car runs just fine. PERFECT EVEN. maybe voltage regulator???


November 22 2011, 12:27 PM
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Post Re: idle drops low for a second when letting off throttle.
That's weird. I get really choppy idle down to near-stall all the time. It also gets worse as electrical load increases. I've always just assumed it was due to running on 3 cylinders.

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November 23 2011, 12:51 AM
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