Question about 1986 Mazda 626 Coupe

6 Answers

High idle 1997 Madza 626 4 cylinder auto transamission

My Madza has a very high idle when I start it up and slowly reduces to about 1000. When driving and slowing down to stop the rpms will go down to about 1100 when they jump back up to close to 2000 rpm before going back down when I finally stop. If I shift into neutral when slowing down to stop, the rpms stay around 1800 all the way until I stop rolling and a few seconds later suddenly drop to 1000 rpm. engine light on. Madza mechanic said I need new IAC valve. I replaced the IAC valve with a used one I bought and cleaned the throttle body throat and plate very good. No sticking problem here. The car has the same idle speed problems it did before I replaced the IAC valve so I am thinking it is something else. What controls the idle speed. What can make it increase on its own when no one isa pressing opn the gas pedal? Please help.

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  • koecher Oct 19, 2008

    I guess my question was incomplete. What is/are the defective parts causing the high idle, causing the idle speed to jump up about 800RPMS on its own when no accellerator input or staying at 1800+RPMS for a few seconds after stopping before dropping down to around 1000 where it should be?

  • koecher Oct 19, 2008

    No. no vacuum leaks. I had the throttle body off yesterday to install the IAC valve.I inspected everything. Throughly cleaned throttle body installed new throttle body gasket.inspected all hoses. Good work was done. It is doing the same as it was before I replaced the IAC valve. This was the reason I replaced the IAC. I was told the one I have is defective. Now I don't think it was.
    I disconnected the electronic lead from the IAC valve and drove and it had absolutely no effect. Still has the high idle/ jumping idle problem. There is some device causing the RPMS to stay in the 1800RPM range when the throttle is closed and RPMS should be less than a 1000. Then all of the sudden the RPMS drop to where they should be. The RPMS, even through the thottle is closed stay 1800+ until few seconds after the car stops rolling.
    Or, if slowing down to stop with throttle closed and as RPMS drop to about 1100 RPMS the RPMS suddenly increast to almost 2000 RPMS. You are trying to slow down and car is speeding up on its own.

  • koecher Oct 22, 2008

    update: had ecm scan run:said IAC valve malfunction. Replaced IAC valve ($500) cleaned throttle body bore, checked all vacumm hoses and reinstalled. Still has high idle(not quite as high)and still does the rpm jumps from 1100RPM to 1800RPM when slowing down and still a few second delay in RPMS dropping to about 1000 once stopped. Still have a problem can not figure out. When driving and shifting into neutral, withour any acellerator input, the RPMS should drop to 1000 or less. In mine they stay 1500+ until after stopping. I have also adjusted throttle body min air adustment to less air. About ready to go back to Madza for that good madza feeling is there a sharp Madza tech out there?

  • Anonymous Mar 12, 2014

    When at ideal the engine speeds up then slows down and keep cycilling

  • Anonymous Mar 12, 2014

    Idle speeds up and slows down at idle isuzu pickup

  • Anonymous Mar 13, 2014

    Engine after warm up the rpm stop on 8:50 rpm then after driving it become ti 1000 rpm

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The PCM controls idle speed to ensure good driveability. The PCM will only attempt to maintain the desired idle speed when it “knows” the throttle is closed. A throttle switch or the TPS input is used to determine when the throttle is in the idle position. Motors and solenoids are used by most PCM’s to control idle speed. Many PCM’s are programmed to attempt to control the idle speed by adjusting spark timing and then by controlling the idle speed actuator. Some computers of the early 80's did not control idle speed.

Posted on Oct 19, 2008

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  • Christopher Baroni
    Christopher Baroni Oct 19, 2008

    The first thing to check for here is a vacuum leak. Sometimes it can be difficult to track down broken hoses, but it takes a large vacuum leak to cause a high idle. Check the rubber hoses that connect directly to the intake manifold and throttle body. These are the most likely to fail. The best way to track down a mysterious leak is to remove a vacuum line and block its source with your finger. If the idle speed drops significantly below where it was before you removed the line, then you may have found your problem. Also look at the gaskets and air ducts between the throttle body and the intake manifold. It is unlikely, but you could have a leaking intake manifold gasket as well.

  • Christopher Baroni
    Christopher Baroni Oct 19, 2008

    The next thing to check is the throttle stop. Also check that the throttle is being completely released against the throttle stop by the throttle cable. If the cable is holding it open, make sure that the accelerator pedal is not caught or binding on anything. Also check that the throttle return springs are in tact. There are usually 2 torsion-type coil springs around the base of the throttle arm and 2 pull-type springs between the throttle arm and the throttle body.

  • Christopher Baroni
    Christopher Baroni Oct 19, 2008

    The last thing to check is the AIS motor. Remove the two Torx screws holding the AIS unit and pull it out.

    If you have a 1987 or earlier Turbo I engine, then look in the end of the motor to see if it is completely shut (see diagram on the right). If it is not, then it may not be working. Reconnect the cable to the AIS motor and have someone turn the ignition on. Watch the valve opening for movement. The valve should close, and maybe reopen. If there is no movement, then you may have a bad or seized AIS motor, or a wiring problem. These motors have a tendency to corrode inside and seize up. You can either try to replace it, or take it apart. There are a lot of little gears and parts inside, so proceed at your own risk. Take it apart carefully and be sure to reassemble it the same way. Pay special attention to the orientation of the rotating valve. Clean up all the parts and take the motor apart. Once the motor is free of corrosion, lubricate the bushings with some engine oil. Do not use any silicon-based lubricants. Reassembling the motor and unit with some RTV will help keep moisture out in the future.

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This is the problem with wiring in the car there is short in the wiring or broken electrical element in the car which is causing this problem ,open hood and check for any broken wires or missing belt in the car..



Good luck..

Posted on Oct 22, 2008

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Hi,

May I offer alternative possibilities... Pls try/check:

  • Idle Up Solenoid For A/C. This may be vacuum operated or an electrical solenoid;
  • Throttle Body;
  • Usually they would surge like you say when the idle up is far too high;
  • On systems with one diaphragm for both idle ups there is usually 2 adjusting screws If you take the vac hose off the diaphragm there will most likely be another screw inside where the vac hose was plugged in.
Hope that this be of initial help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards. Thank you for using FixYa.

Posted on Oct 19, 2008

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Probably you need to connect the car ECM to a scanner and tune up the electronic injection, if this had not been done already , otherwise, as already mentioned, it can be a defective IAC sensor.

Posted on Oct 19, 2008

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Hi,
if i can offer another solution,
do you have air conditioning in the car?
was it on while this problem is going on?

a/c has this idling riser to compensate for the load of the compressor.

maybe this is the fault. as the compressor kicks in, normal rpm appears, as the compressor kicks out, and the idling riser did not go down , then you will have a high rpm.

just a thought,

drcool

Posted on Oct 19, 2008

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  • 306 Answers

 Idles low (500-600) when started in the morning. After initial start, need to give gas to keep it alive and then after some  driving the idle comes up to 600-700 and it will drive OK. so  the "air valve"  has to be  replaced and covered under the emissions warranty.
As far as I can tell, the "air valve" is a small diaphragm-type  valve mounted on the side of the air cleaner housing, and it  switches incoming air into the exhaust system. Else  try  replacing the fuel pump and so it works fine and back to normal and good as new.

Posted on Oct 19, 2008

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HIGH DOLLAR PART, 400 to 500 smackers....

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Anyway, if you want to try cleaning it, try this link... its to a Probe, but should be the same as yours...

http://www.geocities.com/adamk01452/IAC_Clean.html

If its not the same as that, you can probably search the net and find a site specific to your car... but it really should be the same motor, even the haynes manual for the Probe has sections for both the Probe and 626 in it...

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