Hanging High Idle, could TPS Cause?

4 replies to this topic
  • tythew

Posted January 17, 2008 - 08:45 PM


2001 YZ426 with BK mod, E-series exhaust. Seems to run great at all throttle settings, but I can't figure out some issues at idle. Blip the throttle and the idle takes 2 seconds to come all the way back down. This is especially annoying coming into a corner as the bike tries to keep going fter you let off the throttle. With the TPS disconnected the hanging idle is a lot less of a problem, but still there. I went through all the TPS tests and all was fine except the resistance at idle. It was reading ~1.3 k ohms at idle when it should be around 700. I adjusted it, but could only get down to ~1.1 k ohms before running out of adjustment. Another symptom is that when the bike is cold it will barely idle, which leads me to turn the idle up. As the bike warms up after a ways into the ride I have to keep adjusting the idle back down as it keeps climbing. Could the TPS be going bad? Maybe an air leak causing an extra lean condition with no throttle opening? I feel like I am chasing my tail on this one...:cool:
Thanks Guys!

  • grayracer513

Posted January 18, 2008 - 06:49 AM


Check for air leaks. Berrymans' B12 Carb cleaner is excellent for this (careful, it's flammable when exposed to open ignition sources like flames and sparks). Spray the suspected area and the idle will increase if it's leaking.

Also, check the hot start plunger to be sure it's seating. Easiest way is to cold start, and while the choke is on, pull the HS out. Idle should rise and fall again when you close it.

After that, check the valve clearance. A tight intake valve will cause a hanging idle by diluting the intake charge.

When this is done, you will have either found a cause, or eliminated the "normal" possibilities. Then return to the TPS. Unplug it. Is the problem gone? If so, the TPS is most likely faulty.

When you're looking at the TPS, perform the test on page 6-8 of the manual:
Connect the VOM leads to the yellow and black wires of the disconnected sensor and check the resistance at both open and closed throttle. It calls for 0-2kΩ closed, and 4-6kΩ open. Open the throttle slowly, and watch the meter to see that the resistance climbs smoothly from the low reading to the high with no sudden jumps either way.

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Posted January 18, 2008 - 06:53 AM


partially blocked pilot jet / pilot circuit .

  • grayracer513

Posted January 18, 2008 - 07:17 AM


partially blocked pilot jet / pilot circuit .

I was kind of assuming he had gone through an attempt to adjust the idle circuit already, but yeah, that should be checked out too.

  • bigdrtrdr

Posted January 18, 2008 - 01:16 PM


Check the throttle slide for a crack, These are notorious for this.
Ive seen one that chipped and nuked a freshly rebuilt top end.

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