Trucks randomly idling slow/stalling

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Aug 2, 2017
Tustin, California
I've had zero issues with my 80 since I've owned it. I had some serviced done at the dealer, picked it up a few weeks ago, and it stumbled from 800rpm down to 200rpm with a vibration. I turned it right around, picked it up the next day and they told me they did a complimentary throttle body service and it was idling "strong".

This morning, I replaced my PCV valve with no issues and cleaned my battery. Normal maintenance. Im driving to work, and here we go.... the same thing. Stop at a light, it starts stumbling and vibrating. Quickly turn around and swap cars. Get back in after work, drive around, truck feels normal and strong as always. My intake boot looks good, fuel filter/air filter/oil filter are good.

Stumped on what to do now... I am thinking that I possible need plugs/wires/distributor. I don't know when this was done last, other than knowing a dealer did plugs 30k ago. Wires dated 1999 Yazaki.

Any help is much appreciated, thanks all.
Replace the fusible link. $8, 20 minutes tops. Cheap to find out.
Pull, clean, and reset your idle air control valve. Clean the throttle body where it enters. Test the EGR modulator, VSV, and run a wire through the vacuum channel that passes between the two through the intake manifold.

I had weird, intermittent low idle and stalling. My IAC was gummed up and carbon had packed into the vacuum lines after the EGR modulator, which interfered with the VSV.

And if you're not sure about the ignition system, replace the distributor and rotor with Toyota parts. In my past experience on other vehicles, they're only good for around 30k miles. Not sure about the longevity of genuine Toyota distributors.
Try looking under the hood at night or in complete darkness, you may have a lead that is breaking down, you do a little maintenance and the lead gets moved only to vibrate back to its original position where it may short.

The intake boot is a classic, try spraying some throttle body cleaner around intake areas, if it gets drawn in the engine note will change, then you have found your problem, always keep an extinguisher nearby in case it is a fuel leak.


I'm going with TPS monitor. I have this issue with mine intermittently.
TPS monitor?

Sorry. Not drunk. Just sleep groggy. TPS is Throttle Position Sensor. There is a way to check it and adjust it, I believe. I threw a code on my trip out west last year. Replaced it with a used one and was fine for about 11 months but it is doing the same thing again.
I personally would first check the main wire harness that routes next to the EGR valve and ensure the wires are in good shape. Re-wrap with silver thermal/insulated tape. Also remove glovebox and make sure the harness that goes from the ECU out towards the firewall and next to the metal frame behind the glovebox is in good shape.
Does this stumbling only happen after the battery is disconnected?
Does this stumbling only happen after the battery is disconnected?

Nope, i had thought the same thing, but it happens every now and then. Happened 3 times now.
Long shot, but mine did something similar when one of the O2 sensor connectors got wet. I was getting rich/lean code though. Worth a check anyway. I added some dielectric grease to the connector and it resolved my problem.
I would pop the hood in the dark , mist all around plug wires and cap with water..... MIST NOT DROWN!......then fire it up, and watch for a “light show”! Easiest, and most accurate way to check firing system for faults. Good luck!
Double check the rubber air intake hoses. Mine had a crack along the rib and when starting up or idling there was enough vibration to open up the crack and make things vibrate more and rough idle. Eventually the crack got big enough that it would stall the engine, and then I was able to find the crack. The crack was on the bottom of the rubber hose- you really need to remove the hose and pull apart along the ribs to see if there is a crack.

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