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    Thread: 8v has low idle and stall when air conditioning is on

    1. 07-26-2012 08:32 AM #1
      1992 Jetta GL 8v Digi 2 ce2

      Everything works good when the air conditioning is turned off. When I turn on the A/C the compressor engages, and bogs the motor down to 300rpm, and sometimes stalls. It doesn't matter if the engine is cold or hot. The AC blows ice cold, previous owner claims it is still on R12.

      I have replaced plugs, wires, rotor, cap, coil, fuel pump, vacuum lines within the past 1000 miles and have cleaned the ISV, nothing has made a difference is this issue.

      Next on the list to do is ground wires and new o2 sensor.

      The wires on the SD508 Compressor look to be connected correctly, and unmolested, along with noise free operation.

      What else could it be
      Should I try to replace the ISV?

      I would think that if the ac compressor was binding up, the belt would slip.


      Thanks

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      07-26-2012 02:43 PM #2
      you may need to adjust your idle. I also imagine there should be a wire running to the ECU to trigger AC mode idle compensation.

      Otherwise, the ISV should still be able to catch up after the idle dips, and if it doesn't stall, should bring it up to spec.


      Is your idle switch functioning? Do you hear it click when you pull the throttle, and again when you return it to rest?
      I really suck at smog.

    3. 07-26-2012 10:34 PM #3
      Quote Originally Posted by ziddey View Post
      you may need to adjust your idle. I also imagine there should be a wire running to the ECU to trigger AC mode idle compensation.

      Otherwise, the ISV should still be able to catch up after the idle dips, and if it doesn't stall, should bring it up to spec.


      Is your idle switch functioning? Do you hear it click when you pull the throttle, and again when you return it to rest?
      I have adjusted the idle set screw. I have to set the idle to 1200 without the ac on, to make the car idle at 900 with the ac turn on. I drove around a day or two with the idle set high, due the 100+ degree weather, the AC was run most of the time anyways. I have since turn the idle back down so that it idles at 900rpm without the ac turned on, and just try to remember to turn off the ac when i come to a stop.

      I'll try to check the Idle switch tomorrow with my meter, and report back.

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      07-26-2012 10:46 PM #4
      you shouldn't need a meter to check the switch although that's certainly a definitive way to test. usually, if it gets misaligned enough, you simply will no longer be able to hear it click.

      as for your ISV, is it buzzing when the key is in the on position but not started?

      even without the ac trigger, the ecu should still be trying to maintain programmed idle speed. it should usually catch it before it falls to low, although I can see with the extra load on the engine from the AC, it may not be quick enough.

      do check that the idle switch is working. If the ecu doesn't think it should be idling, there may be improper ISV behavior.
      I really suck at smog.

    5. 07-30-2012 11:38 AM #5
      The idle switch was not getting engaged. With a little adjustment it is working properly now. Idle is better, less stalling with the ac on. However, Idle and power is way down when the ac is on. I measured the voltage on the battery while at 3000 rpm, and only got 13.34 volts. and only 12.04 when idling.

      While the Alt is working, it's not up to spec per the Bentley. Could a bad or weak alternator cause my problems?

      Quote Originally Posted by ziddey View Post
      you shouldn't need a meter to check the switch although that's certainly a definitive way to test. usually, if it gets misaligned enough, you simply will no longer be able to hear it click.

      as for your ISV, is it buzzing when the key is in the on position but not started?

      even without the ac trigger, the ecu should still be trying to maintain programmed idle speed. it should usually catch it before it falls to low, although I can see with the extra load on the engine from the AC, it may not be quick enough.

      do check that the idle switch is working. If the ecu doesn't think it should be idling, there may be improper ISV behavior.

    6. 07-30-2012 11:44 AM #6
      I also checked resistance on my ground points under the hood. All measures under 8ohms. The chassis connection beside the battery tray is a little rusty, and I've also noticed a faint glow on my turn signal indicator on the cluster.

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      07-30-2012 01:17 PM #7
      8ohms is A LOT.

      What do you mean by idle and power "way down"? Idle speed lower than it should be? Horsepower down? Voltage down?

      Now that the idle switch is verified to be working, how does it normally behave coming down to idle? Perhaps it's time to play with the idle screw again. Do you have a Bentley?


      Power should not be affected. If it is, is the idle switch sticking now?

      12.04v idling, 13.34v at 3000rpm. What kind of electrical load are you placing? AC fan on high? Headlights on?

      Assuming you have an old Bosch alternator, the voltage regulator is installed with two phillips screws. Takes a minute to remove. Examine the brushes. A new one is cheap.

      http://www.autohausaz.com/search/pro...ge%20Regulator

      Bosch is $29.


      Do triple check you don't have any vacuum leaks
      I really suck at smog.

    8. 07-30-2012 05:29 PM #8
      Quote Originally Posted by ziddey View Post
      8ohms is A LOT.

      What do you mean by idle and power "way down"? Idle speed lower than it should be? Horsepower down? Voltage down?

      Now that the idle switch is verified to be working, how does it normally behave coming down to idle? Perhaps it's time to play with the idle screw again. Do you have a Bentley?


      Power should not be affected. If it is, is the idle switch sticking now?

      12.04v idling, 13.34v at 3000rpm. What kind of electrical load are you placing? AC fan on high? Headlights on?

      Assuming you have an old Bosch alternator, the voltage regulator is installed with two phillips screws. Takes a minute to remove. Examine the brushes. A new one is cheap.

      http://www.autohausaz.com/search/pro...ge%20Regulator

      Bosch is $29.


      Do triple check you don't have any vacuum leaks
      Picked up a brand new Bosh alt from a friend for $40, even if I don't need it, it's good to have a spare.

      I do have a Bentley.

      I've triple checked for vacuum leaks, I even temporally plugged off the vac lines to the charcoal canister, no difference, so I hooked i back up.

      I did check the brushes on the alternator. They were pretty worn, one looked about 10mm and the other about 7mm long.

      I made 30 mile trip, with out ac in 110*F heat, car did fine for about 10 miles, and then started loosing power, felt like running out of gas. It kept getting worse, if I pressed the gas pedal it would bog down even more. Barely made it back home. Looks like the recently replaced fuel pump is failing.

      What do you mean by idle and power "way down"? Idle speed lower than it should be? Horsepower down? Voltage down?
      very low power, barely take off in first gear with ac on, once up to 2-3k rpm it pull a little better, but far from what it should be. Idle is also low. voltage dummy light never comes on (unless idling very low)

    9. 07-30-2012 05:30 PM #9
      so, next on my list..

      Ground wires,
      replace alternator
      replace fuel pumps.


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      07-30-2012 07:26 PM #10
      try disconnecting them and cleaning the contacts. it'll give you a chance to examine the wires to some extent as well. chances are, they're fine. that or you're using a not-too-good multimeter maybe? the cheap ones sometimes really struggle with the ohmmeter.
      I really suck at smog.

    11. 07-30-2012 07:49 PM #11
      it is a cheapy.. I did measure the resistance from the negative terminal to the edge of the clamp, it was 8ohms too.

    12. Member Seax_Smith's Avatar
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      08-02-2012 11:20 PM #12
      Start at the green wire @ pin 26 of the ECU. This is how digi knows to bump the idle with the AC on.

      First junction is a white, 2X, connector below the brake booster and will probably have a blue wire on the other pin.

      Trace that wire and you will probably find your issue. You will be going from the ECU connector to the fuse / relay panel to the HVAC (and some internal connectionion in the fuse / relay panel) and then out to the compressor and back.

      Also look carefully at that tangle of Red/Whites associated with the relay screwed onto the radiator fan shroud.

      That green wire and that tangle of Red/Whites is why my car is now wired as a non AC car.
      I'm currently out of my mind, but feel free to leave a message.

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