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Thread: Aircon and engine cutting out(with engine light) when moving from stop

  1. #16
    Forum Member 1st year Apprentice
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    Default Re: Aircon and engine cutting out(with engine light) when moving from stop

    Quote Originally Posted by ajh
    The easiest way to check the operation of the ISC valve is to start the car, then turn on the A/C. When the compressor cuts in, you should hear the engine idle speed dip slightly for about 1/2 a second, then go back up to normal idle speed.

    When the compressor cuts out, the idle speed will go up slightly and drop back down to normal speed.

    Put simply, its purpose is to maintain the idle spped at a constant level when various loads are put on the engine. EG: A/C, Power Steering, etc.
    when i turn on the AC, it does that.

    although its constantly at 1000rpm. UNLESS i short the terminals that give me a code, then it goes up a little for 5 secs, and then drops down to 700rpm. I've taken this out of the WS manual for testing the ISC valve.

    When you had your ISC/TB problem, did yours idle at just over 1000 ?
    Last edited by Thraxeh; 02-12-2006 at 04:48 PM.

  2. #17
    Junior Member Grease Monkey
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    Smile Re: Aircon and engine cutting out(with engine light) when moving from stop

    Mine only idled fast for a couple of secs when I shorted out the diagnostic terminals ( as per the w/s manual)

    It then dropped down to normal. 650-700 rpm.

    Under normal driving conditions, mine would idle ok, a little fast, which I found the ignition timing was advanced way too far, so that was easy fixed. however when the A/C was switched on, the engine would nearly stall, then crank itself up again. This would repeat over and over until the A/C was switched off. The tacho needle would bounce up and down like a yo yo while this was happening, and the A/C compressor would cut in and out constantly.

    I'm assuming you've checked the output of the A/C amplifier to eliminate that as a possible source of the problem. ( the w/s manual has a procedure for checking this too) It plays a role in sending a signal through to the ISC valve.

    To test it, you need to have the engine running with the A/C on. On mine, I had to manually wind the idle speed up so the car would idle with the A/C on to perform the test. The idle speed screw is on the top of the throttle body. Wind it anti clockwise to increase the speed and vice versa to decrease.

  3. #18
    Junior Member Grease Monkey
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    Smile Re: Aircon and engine cutting out(with engine light) when moving from stop

    Sorry, One other thing I forgot to mention,

    On the opposite end of the manifold to where the throttle body sits, you will see a device ( not sure of the correct name for it, some sort of adjustable modulator perhaps???) with vacuum tubes connected to it and a spring loaded knob in the bottom of it., they are tied in with the ISC valve and to another electrically operated vacuum switch mounted on the firewall.

    On the electric vacuum switch, do a quick check with your multimeter to make sure the switch is operating. From memory, I think it has voltage applied to it when the A/C is off and no voltage when the A/C is on. ( again, the manual will show you in more detail)

    Also, just check all those vacuum lines to eliminate the possibility of a split or broken line making the idle speed go crazy. In particular, the big vac hose that runs from the ISC valve to the other end of the manifold. Mine literally crumbled when I disturbed it!!

    I'm seriously thinking of buying a load of shares in one of the companies that manufactures vacuum hose. With all these people working on old toyotas, (camrys in particular) there's a fortune to be made!!!!!!!!!

  4. #19
    Forum Member 1st year Apprentice
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    Default Re: Aircon and engine cutting out(with engine light) when moving from stop

    Quote Originally Posted by ajh
    Sorry, One other thing I forgot to mention,

    On the opposite end of the manifold to where the throttle body sits, you will see a device ( not sure of the correct name for it, some sort of adjustable modulator perhaps???) with vacuum tubes connected to it and a spring loaded knob in the bottom of it., they are tied in with the ISC valve and to another electrically operated vacuum switch mounted on the firewall.

    On the electric vacuum switch, do a quick check with your multimeter to make sure the switch is operating. From memory, I think it has voltage applied to it when the A/C is off and no voltage when the A/C is on. ( again, the manual will show you in more detail)

    Also, just check all those vacuum lines to eliminate the possibility of a split or broken line making the idle speed go crazy. In particular, the big vac hose that runs from the ISC valve to the other end of the manifold. Mine literally crumbled when I disturbed it!!

    I'm seriously thinking of buying a load of shares in one of the companies that manufactures vacuum hose. With all these people working on old toyotas, (camrys in particular) there's a fortune to be made!!!!!!!!!
    yes, i found this, although i dont think its linked to the ISC, as it bypasses the throttle body(its on the other side of the plenum), and lets in air that way.

    I found that the AC Idle up is working perfectly, i also screwed the idle screw on the throttle body to decrease the idle, but its still at 1000rpm, but the engine noise did change to sound like it was at a lower RPM.

    vacuum lines seem fine as well.

    i have to do some tests on the ECU, and see that its recieving the signal's it needs

  5. #20
    Junior Member Grease Monkey
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    Smile Re: Aircon and engine cutting out(with engine light) when moving from stop

    FYI: It's a bit hard to see, but if you put your hand down under that vacuum thing I was referring to, you will feel a large vacuum hose connected to the bottom it. This hose runs down to a steel tube which runs across under the manifold, and has another rubber tube on the other end going up to the ISC valve.

    Do you have a tachometer / multimeter that you can connect up to check the idle speed?
    I found the tacho on the car is not the most accurate.

    I bought one from Supercheap Auto ( if they exist in NSW) for $39. It's a handy thing to have as it is also a multimeter and measures dwell too.

    By the way, did you check the A/C amplifier to make sure it's working?

    With the fast idle, it may even pay to check your ignition timing. As I said with ours, it was advanced too far, not enough to ping ( the rattling noise under heavy load) but it was causing the idle speed to increase somewhat.

    Anyway, keep us informed on what you find.

  6. #21
    Forum Member 1st year Apprentice
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    Default Re: Aircon and engine cutting out(with engine light) when moving from stop

    Quote Originally Posted by ajh
    FYI: It's a bit hard to see, but if you put your hand down under that vacuum thing I was referring to, you will feel a large vacuum hose connected to the bottom it. This hose runs down to a steel tube which runs across under the manifold, and has another rubber tube on the other end going up to the ISC valve.
    oh right, i didnt see the vacuum hose.

    I'm sure the tacho is correct, when i put the ECU into diagnostic mode revs dropped to 700rpm(you could tell from engine noise) and the tacho showed the correct RPM.

    i'm not 100% sure on the AC amplifier, Although after fiddling with the AC idle up, i loosened the screw which gave the car more revs with AC on, i tested the car and it seems its not stalling when i accelerate from stand still.

    But still the Idle problem is still there.

    not sure how to check the ignition timing though, but i'm sure this wouldnt be the cause, as the car does run at 700rpm when i put it into diagnostic mode..

  7. #22
    Junior Member Grease Monkey
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    Smile Re: Aircon and engine cutting out(with engine light) when moving from stop

    The ignition timing being out is unlikely, but worth checking if you have a timing light.

    All you do is connect the light up to #1 plug lead and a power source, put the jumper wire in the diagnostic plug, start the car, ( turn all acessories off) and aim the light down at the crank pulley.

    You'll see the timing mark on the pulley and the indicator on the timing belt cover. When the strobe in the light is flashing, it will flash on the mark on the pulley ( optical illusion will make the pulley look like it's not turning) the mark on the pulley will line up somewhere on the indicator on the belt cover. eg 10 degrees BTDC. ( check the manual for the correct setting) If necessary, loosen the two bolts on the distributor slightly and turn the distributor body a bee's dick in either direction to retard or advance the timing. Tighten bolts and re-check.

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