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87 Toyota pickup high idle low voltage

Old 05-13-2019, 04:46 AM
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87 Toyota pickup high idle low voltage

Hi guys,
i have an 87 pickup with a 22r that I rebuilt about 12,000 miles ago. I started having issues with a very high idle (around 1800-2000) after the freeway drive to work. When Iím driving city, the charge light on the dash flickers but the idle remains where it needs to be. After 20 minutes or so if freeway driving the charge light in the dash and the emergency brake light turn on and the idle shoots up when I come to a stop. Iím at a loss and wanted to see if you had any ideas.
Timing is correct, electronic fuel pump put on about 8,000 miles ago and no vacuum leaks that I can find.
thank you
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Old 05-13-2019, 06:49 AM
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Start with a multimeter. Check first that you batter is fully charged. Then start the truck and see what the alternator is putting out.

I just had a similar issue with a New From Toyota alternator on my wife's 98 3.4. Drove fine then she started getting weird lights on the dash. Then the battery puked. She did not have a charging gauge so I could not find out if it was charging intermittently or just died. Put a new alternator in it after exchange and runs fine.

And my 99 silverado all of the sudden started randomly flashing the charging light. She drove it home and it was fine. I started it the next day and no lights on dash, charging about 14V on the dash gauge and 14.2 with my multimeter. So I jump in and take it for a drive. About a mile down the road light is on and gauge is reading under 10 volts charging. Drove it home and it went between 10 volts and 14 on the gauge and when low charging I got random dash lights. Put a new alternator in and problem solved.

Last edited by thefishguy77; 05-13-2019 at 06:50 AM.
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Old 05-13-2019, 06:53 AM
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Do you think the truck could be using the high idle as compensation for the alternator not putting off enough power? I just have no idea where the high idle is coming from because it was all perfectly dialed in before this started. Thank you for the reply!
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Old 05-13-2019, 07:15 AM
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Unfortunately I don't know a lot about 22r, carbed, motors. But I don't think the truck is doing the high idle thing as compensation. I suspect there is either a bigger electrical problem, make sure all ground wires are in good condition, search big 3 upgrade. I can see bad grounding causing electrical gremlins. I found some 4/0 welding wire on fleabay and used that to replace all my major grounds. I didnt have a electrical ground related issues at the time. I was just rebuilding the motor so getting to all the ground wires was very easy at the time. As a bonus I have enough extra wire to upsize wires down the road for my winch and similar items.

Ground wires can look good but have corrosion under the insulation that you cant see. You could test resistance with a multimeter if you want. But its pretty much impossible to have too much grounding.
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Old 05-13-2019, 09:30 AM
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I know even less than thefishguy77 about the 22r, but it's really unlikely that your high idle is coupled to your alternator issue.

First, diagnose the "alt" light. Put your multimeter right on the battery posts when you have the alt light. You should get 13.9-15.1 volts. If it's below 13v, the alternator is not charging. If so, reach up and push the throttle to rev the engine up a bit. Does the voltage rise more than one volt? You could have a slipping belt, high-resistance wire, or other problems. Flickering alt light also suggests inadequate charging voltage.

Any change in idle or engine speed while pressing on the brake pedal points to a leak in the power brake booster system. Carefully apply and release the brake when you have high idle; any change in rpm?

While you've got the hood up, check the level of brake fluid. It shouldn't turn on the alt light, but will turn on the brake light.
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Old 05-15-2019, 10:54 AM
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Does the high idle and the charge & brake lights happen at the exact same time?

The engine has no way to compensate for low alternator output so the high idle and charge & brake lights are most likely two separate problems but one problem may be affected by the other, giving you these symptoms.

Just curious, why did you install an electric fuel pump?

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