UPDATE ( Harmonic Balancer failure ) Cold idle stumble 1fz (1 Viewer)

[Dullyouth]

I’m not sure to call it a stumble or a miss or something else. It’s hard to trouble shoot because it disappears once the engine idles down/warms up, does not leave me much time to poke around while the issues is present. I’m preparing to start an intake tear down to try and tackle my persistent P0401. Vacuum hoses, Pcv etc. Plugs are due as well. No electrical modifications/add ons. I noticed that the voltage takes about a .3 to .5 volt hit when this
Issues is happening. I have an obd2 ble ( veepeak ), using OBD fusion. No other codes or faults besides the 401.
Here is a YouTube link of the noise

Fzj80 startup idle noise


95 299500 miles
Edit: also searched for cold idle issues, couldn’t find anything that sounded or described what’s occurring here

 

[LandLocked93]

What does it do if you depress and release the brake pedal while it's doing that?

edit:after a few more watches, I think a whistley brake booster is the least of your worries.
It goes away when it warms up?? It sounds like something is spinning up when the rpms and voltage drop.
And the weird whistle noise...or is that beep from an electric device you have in the truck?

 

[Dullyouth]

Found some posts on the TPS and idle variances. I decided to unplug the TPS and give it a start. The noise and stumble disappeared. I cleared the TPS code that was generated from having it unplugged and started the engine again later in the day(TPS plugged back in)... Still no noise or stumble. This morning on a dead cold start ( sitting all night @ 45 F ) No noise or stumble. OBD monitor says that absolute throttle is somewhere just north of 11% during startup idle where the FSM states it should be set at.
Maybe the TPS had a bad connection? Im not sure. but it seems to be alright for now. This was a strange issue that did not present like anything that I read of other peoples experience with faulty TPS units.

 

[Dullyouth]

Just got around to pulling some things apart further. I discovered that the HB has failed. I can spin the hub independent from the pulley. So the video above is a good example of what a failed HB sounds like.

 

[BILT4ME]

Just got around to pulling some things apart further. I discovered that the HB has failed. I can spin the hub independent from the pulley. So the video above is a good example of what a failed HB sounds like.

There was someone else here recently that was having issues while driving that made noises and RPM changes like this. Had similar mileage. I wonder if that's the same situation?

 

[dallen341]

I have a Harmonic Balancer in Upland. PM me if interested.

 

[Kernal]

Interesting, the voltmeter needle goes up in sync with the noise, so
it must be driving the belts (volts go up), then slips (volts go down)??

 

[Dullyouth]

Ran the LC for a while with a used HB that I picked up from the classifieds a while back. Its been running great, no noise / stumble or charging issues.

Since I was in there
~ Coolant Flush (Zerex Asian Green)
~ Radiator hoses
~ Water Pump
~ Thermostat / seals
~ Constant torque clamps
~ Front main seal
~ Oil Pump seal
~ Distributor seal
~ Distributor cap and rotor


Here is a short youtube clip of the old HB
Failed Harmonic Balancer