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idle surge
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TOPIC: idle surge

idle surge 15 years, 1 month ago #1109

"Rather urgent help needed to diagnose/fix a surging idle problem on my 944. Today we replaced the dampers, bled the brakes, and took the slack out of the throttle cable on an aftermarket throttle cam. Upon restart, the idle immediately started to repeatedly lope between 1000 and 1800 rpm.

Initially we thought the throttle cable was too tight. Slackening the throttle cable did nothing...nor did removing the fuse for the cruise control, disconnecting the idle control valve plug, or just about anything else we could think of to do. Disconnecting the electrical plug into the throttle body caused the idle to jump to and hold at about 3000 rpm, but reconnecting this connection (after cleaning both ends) resulting in the problem immediately reemerging.

Prior to this, I had experienced no problems with idling at all, and the only throttle/idle-related change we made today was tightening, then slackening the throttle cable.

Any suggestions or help is much appreciated!"

Re:idle surge 15 years, 1 month ago #1110

I would guess vacuum leaks but I really don't know what changed when you put on the new cam . maybe the J boot or the vacum hose under it ???

Re:idle surge 15 years, 1 month ago #1113

  • vwmann1
  • Comp School
  • Posts: 25
It has to be a vacuum leak somewhere. It is loaping because the ISV is trying to stabilize and when it does there is too much air. Did the intake boot crack? Did the vac line the runs under the TB break?
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