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 92 MX-3 GS 1.8L - engine revs up and down 
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Joined: May 25 2002, 2:01 AM
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Location: CFB Val-Cartier, Quebec, Canada
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Post Re: 92 MX-3 GS 1.8L - engine revs up and down
The idle bounce happens when the car idles (at hot) at around 1500rpms, so then it starts surging. Check at the cause that's not the surging, but why your idle is at or above 1500. The higher your idle is, the faster it will bounce, so if it wants to idle at say 2200, it'll bound faster than if your idle would be at 1500rpms.

Turning on the A/C sends a signal to your ECU to adjust the idle because of the extra load on the motor.

My suggestions:
1) Do as the guys suggested and start with a TPS and idle screw adjustment. As a test, try to get the idle as low as you can, even if it's too low and will stall, at least it'll give you a starting point to work your way back up.
2) Try this again with the IAC unplugged.
3) If you can't get the idle low enough, look into vacuum leaks.

I had an issue with a vacuum leak that was internal to the bored out throttle body I had. I made a switch to turn the IAC on for cold starts (otherwise the idle was really low) but turned it off when she was up to temp because the idle was too high when warmed up. Having just touched your TB, it would be a leak somewhere in there, or maybe you disturbed the accordian tube for the intake, they do tend to crack with age.

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1992 Mazda Mx-3 GSR - 2.5L KLZE : Award Winning Show Car & Race Car ['02-'09] (Retired)
2004 Mazda RX-8 GT - Renesis Wankel : LS3 Coils, BHR Mid-Pipe + Falken RT-615K 245/40r18
2011 Mazda Mazda2 GS - 1.5L Manual : Yozora Edition (1 of 500)
2003 Nissan Xterra SE - 4x4 Supercharged : 2" Body Lift, 4" Suspension Lift & 33" MTR Kevlar
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February 14 2014, 1:02 PM
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Joined: February 05 2014, 7:33 PM
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Post Re: 92 MX-3 GS 1.8L - engine revs up and down
The throttle body fixed the idle problem.. It settled right down to 750 immediately after putting it on.. Even without adjusting anything.. but I still plan on adjusting the TPS, idle speed and ignition timing before I get it smogged. For now, the idle is smooth as butter.


February 14 2014, 2:53 PM
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Post Re: 92 MX-3 GS 1.8L - engine revs up and down
adjusted the idle screw.. got the idle rock solid at 650 out of gear.. 725 +/- in gear.


February 14 2014, 4:50 PM
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Post Re: 92 MX-3 GS 1.8L - engine revs up and down
gonna do the ignition timing since it's dark.


February 14 2014, 10:44 PM
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Joined: March 08 2010, 8:21 PM
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Location: Canandaigua, NY
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Post Re: 92 MX-3 GS 1.8L - engine revs up and down
glad that worked out for you :wink:

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February 14 2014, 11:39 PM
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Post Re: 92 MX-3 GS 1.8L - engine revs up and down
Yeah thanks Glen it really came through. It feels real good and sounds good.


February 15 2014, 3:04 AM
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Post Re: 92 MX-3 GS 1.8L - engine revs up and down
The old TB was glued on to the IM plus the top TPS screw was broken off at the head of the screw so yeah


February 15 2014, 3:09 AM
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Post Re: 92 MX-3 GS 1.8L - engine revs up and down
ignition timing set 10-11* btdc.
neutral idle speed rpm rock solid 650 assuming the first notch on the tach is 500rpm. While in gear +50.
tell me if this sounds right.


February 17 2014, 4:08 AM
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