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1998 Mazda 626 idles rough. How can I adjust idle speed?
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plsmoothy
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Jun 10, 2009, 11:48 AM
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1998 Mazda 626 idles rough. How can I adjust idle speed?
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Hi community. I drive a '98 Mazda 626LX 2.0L 4Cyl with 140,000 miles. The car idles at approximately 650 RPM. At this RPM, I get an intense vibration in the engine and throughout the car. Here's what I've done in an attempt to eliminate the problem. 1. Changed spark plugs/spark plug cables. 2.Checked engine compression... compression good. 3.Removed fuel injectors and had them ionically cleaned. 4.Checked for error codes ... none found. 5.Replaced fuel filter.
At this point I'm considering changing the motor mounts. Before I do that however, I want to increase the idle speed by 100 RPM or so. Can anybody shed some light on how to go about in doing this? Also, any other insights are greatly appreciated.
Thanks
(This post was edited by plsmoothy on Jun 10, 2009, 11:49 AM)
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Hammer Time
Ultimate Carjunky
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Jun 10, 2009, 12:02 PM
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Re: 1998 Mazda 626 idles rough. How can I adjust idle speed?
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The idle for that car is entirely controlled by the computer and not adjustable in any way.
If your getting a vibration, the motor mounts will likely cure it.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Loren Champlain Sr
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Jun 10, 2009, 1:08 PM
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Re: 1998 Mazda 626 idles rough. How can I adjust idle speed?
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Cleaning the throttle body and idle control motor may help.
Loren
SW Washington
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Hammer Time
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Jun 10, 2009, 1:12 PM
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Re: 1998 Mazda 626 idles rough. How can I adjust idle speed?
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Loren, The idle is right where it should be. He just thinks if he runs it higher, the vibration will go away.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Sidom
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Jun 10, 2009, 6:01 PM
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Re: 1998 Mazda 626 idles rough. How can I adjust idle speed?
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At that mileage it is very possible it's your motor mounts. To verify this if you put a floor jack under the engine & slightly jack up engine (with a piece of wood or something so as not to damage the pan) to take take the weight off the mounts & your vibration goes away( while the engine is running), then it's the mounts for sure.....
(This post was edited by Sidom on Jun 10, 2009, 6:01 PM)
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plsmoothy
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Jun 11, 2009, 1:18 PM
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Re: 1998 Mazda 626 idles rough. How can I adjust idle speed?
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Don't want to beat a dead horse here but is there absolutely no way to reprogram the computer to increase the idle speed? An increase of 100-150 rpm's seems to make all the difference in the world.
Thanks again.
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Loren Champlain Sr
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Jun 11, 2009, 3:03 PM
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Re: 1998 Mazda 626 idles rough. How can I adjust idle speed?
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plsmoothy; The idle spec for your car is 550-800rpm, so as Hammer stated, it is within specs. And, as he said, the idle speed is computer controlled. If the engine is running rough and is within idle specs, you have an underlying problem that is causing the roughness. Changing the motor mounts won't fix the roughness. May even make it more noticeable.
Have you had the injectors ohm checked? Have you cleaned the throttle body and IAC? Compression test? Valve clearances? So many things can contribute to this.....No easy answer.
Loren
SW Washington
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plsmoothy
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Jun 11, 2009, 6:22 PM
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Re: 1998 Mazda 626 idles rough. How can I adjust idle speed?
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I'm in the process of cleaning the throttle body and idle air control (AIC) now. I noticed there is quite a bit of a tar like substance in the intake manifold. Should I clean the intake manifold since I'm already in the vicinity?
I took the advice of Sidom and loosened up a couple of the motor mounts, put a jack under the oil pan and lifted the engine. The vibration felt pretty much the same. Does that prove that it's not necessarily the motor mounts.
In addition there is something that I forgot to include in my original post. The idle gets rougher when I turn on the Air Conditioner. The vibration gets really intense.
As always, your help is greatly appreciated.
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Sidom
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Jun 11, 2009, 6:44 PM
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Re: 1998 Mazda 626 idles rough. How can I adjust idle speed?
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Sounds like the intake is pretty dirty. Cleaning the throttle plate is good but most shops offer services that run cleaning solvent thru the intake & also disable the fuel system & run it thru the rail also to clean the injectors.
The method I told you about you don't loosen any of the mounts, just put a just under the pan w/wood & a couple of pumps to support the motor & run it. On the ones I've done that had bad mounts this would either eliminate the vibration or make a noticable improvement.
Now I'm assuming you've check all the mounts & none are broken. This method is only to check mounts that have hardened & are transmitting the engine vibration..
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Guest
Anonymous Poster
Sep 11, 2009, 7:44 AM
Post #10 of 10
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Re: 1998 Mazda 626 idles rough. How can I adjust idle speed?
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Hi there,
I have a 1993 and the same problem. To adjust the idle the computer needs to be re-adjusted. Place a wire between TEN en GND inside the diagnoses connector. Adjust the idle with the flathead screw on the right top side of the t throtthle body. Rotating counterclockwise will rise the RMP. Turn the car of and remove the wire. I have tried it and the RPM are now 950 rmp but it is still a little bit rough. Also cleaned the EGR valve, clean the IAC valve, cleaned the injector etc....
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