Question about Mazda 626

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My 1998 mazda 626 will not run smooth when she is idling the rev counter will go from 1000 rpm to about 500 rpm and back up again and sometimes she will just cut out because its gone that low the choke works fine though on drive you wouldnt think there was any problem she drives has smooth has butter

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  • tistara Nov 02, 2008

    No it happens after the automatic choke has gone off and she is left to idle, also it does it after standing stationery after driving

  • tistara Nov 02, 2008

    Ah there is white smoke coming out of the exhaust but not as only at the start of start up.

  • tistara Nov 02, 2008

    Can I say there was a split in the exhaust pipe near the manifold so I had a mechanic weld the split together it was after this little operation that the car started doing this, I was told that using an electric welder could damage the computer brain in the car, could this mechanic be the cause of the problem, I am not saying he was, just could the work he did have caused it.

  • tistara Nov 02, 2008

    Will check that out Chad thanks

  • tistara Nov 04, 2008

    Thanks I wioll have all these suggestions printed out and have a mechanic look at them will get back to you all

  • tistara Nov 04, 2008

    I have had a mechanic look at it and the sensor that is connected to the top of the exhaust near the manifold is broken, it is also leaking exhaust into the engine so it looks like the sensor and the exhaust leak is the problem, its going to cost £100.00 for a new sensor plus the bit of the exhaust near the manifold, this guy who supposed to have fixed the exhaust seems to have broken the sensor and made a botched up job of the exhaust so that has to be paid for also.

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7 Answers

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First: check to see if your oil is a milky color, if it is this is a sure sign that the head gasket is blown and needs replaced. The white smoke is a tell tale sign as well. as is loss of coolant.
second: when was the last time that your car had a complete tune up, plugs, wires, rotor, cap, including air filter and the engine timing checked.
third: the exhaust leak can cause this type of problem.
also check all of your vacuum lines, throttle body, and intake manifold gasket for vacuum leaks.
Good luck and remember to rate all solutions you get on FixYa, thanx.

Posted on Nov 04, 2008

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Hi

It certainly sounds as if a metering vacuum hose has been dislodged or probably overheated and now leaking from the mechanics work about the exhaust manifold. paying careful attention in this area may provide the solution to the problem you have. Always a good idea to backtrack the problem to when it started to occur and then try to determine if it was actually a man made problem. Is what I would be looking for at this point. It may well be the oxygen sensor/wiring to same that is causing the problem.

regards
robotek

Posted on Nov 04, 2008

  • Graeme Ross
    Graeme Ross Nov 04, 2008

    fantastic... so my recommendation to you was accrate and worthwhile, the oxygen sensor was the problem, broken by the previous mechanic. Just wondring why you have not accepted my solution. This is how we are paid for providing you this service.

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I do not think that any welding job done on the exhaust, even using an electric welder can damage the computer module. At least if this is even possible, it is rather unlikely.

From description the car looks like there is more then one problem.

The rev counter will go from 1000 rpm to about 500 rpm and back up again, and behaving erratically may be because there is a problem with idle and fuel settings . A car ECU code reading will probably tell you more about this.

If the car is emitting white smoke from the exhaust, check also the water level.
If the level in the water tank is going down after driving the car for a while, that may be a symptom that the head gasket is starting to go, and water is being vaporized inside the engine.

Posted on Nov 02, 2008

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Dear Sir/madam,

The first step must be to determine whether the sensor is bad, or it's being sent gases out of normal parameter. It's possible to have an excessively rich or lean condition, a less that healthy engine, an egr problem, and a few more. You probably will have to pay a talented professional to deal with this. You need to isolate the cause of the signal problem. Personally, for no particular good reason, except "hunch", I suspect the egr or idle system. I'm curious now, let me know how this goes......

Checked and cleaned MAP sensor and idle air valve. No help. During low engine speed there is a loud sound from the valves however it stops at 3250 rpm and above and runs good at high rpm. I checked the timing and its way off. When it is able to idle the timing is off the scale to the left. Could it be a sensor that changes the timing or has the timing belt sliped?

Verify all the basic engine parameters, cam timing, compression, ignition timing. You can't go after the tricky stuff until you're certain the basics are perfect. The ecm(engine control module) controls almost everything, and can only react based on the premise that all the sensors, etc are attatched to a "normal" motor. The loud sound from the valves doesn't sound like a good thing. If everything else checks out ok, that's a symptom that needs to be investigated. Most of the time, everything is pretty much cause and effect.


Thanks

Posted on Nov 01, 2008

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Check to see if there is any smoke coming out of the exhaust pipes. If there is, then you may need to get a new engine because a head may be blown, and if there is not, make sure you did not just change fuels suddenly. This could clog up the fuel pump causing the rpm's to lower. You may need a new fuel pump or fuel filter.

Posted on Nov 01, 2008

  • Jazz Boyce
    Jazz Boyce Nov 02, 2008

    And if it happened after the mechanic did work on the car, you will need to take it back to the same mechanic and tell him that after he worked on it, it started to mess up and he will have to fix it especially if you used an electric welder.

  • Jazz Boyce
    Jazz Boyce Nov 04, 2008

    The first mechanic is responsible for what happened and you should take it back as soon as possible to get it fixed for free.

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Tistara hello,

When does this happen? Right after you start the car? After a long drive? Is the air conditioning on?

Posted on Nov 01, 2008

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My guess would be the oxygen sensor needs to be replaced.

Chad

Posted on Nov 01, 2008

  • Chad Houston
    Chad Houston Nov 01, 2008

    Could also be the idle air control valve or a leaking vacuum hose

  • Chad Houston
    Chad Houston Nov 01, 2008

    Now that I have thought about it, I am leaning more towards leaking vacuum hose. Raise the hood and listen for a sucking air sound. It could be as simple as a vacuum hose has come off, or has dry rotted and is leaking. Hope this helps, Chad

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