Hi all,

Been having a weird issue lately with my 1990 runner with a 3vze. It happens in all gear positions including park. The rpms will fluctuate as will the voltage on the dash and aftermarket gauge pod. It bounces between 14.4 to as low as 11.9. It will fluctuate every second. In addition the exterior and interior lights flicker and dim. The only time this condition is not observed is when I'm accelerating and the rpms hit the 3k range.

My thoughts were a bad ignition coil, alternator, or ground cable. Over the last two years I have replaced probably 80% of everything on this engine to include battery, terminals, plugs, wires, cap, rotor, most sensors, coil, tps, alternator, and alternator charge wire. The alternator is a 130 Amp from LCE so I would doubt that route as I have had excellent luck with their products. I also keep the motor very clean including a cleaning of fhe throttle body and manifold when I pulled it to replace the valve cover gaskets. Any help is appreciated!

 

Still sounds like a charging (alternator) issue, though the first place to start is with the battery. Charge the battery and check your voltage while running.

If the engine RPMs bounce up and down there alternator output will also bounce up and down.

 

I will do that and check it with my multi meter. Terminals appear fine with good connections as do the connections at the motor and starter. The plug at the back of the alternator was a tad loose, made a slight click upon pushing it in but not a click as if it was fully seating after having been unplugged. Issue still remained after the motor warmed up after a minute or so. Also of note is I had upgraded to a thicker gauge (8 I believe) charge wire, those connections are also solid.

If this helps I noticed when blipping the throttle the voltage will dip real low and idle down to the 400s range, hold for about 8 to 10 seconds then rise back up maybe as if its getting enough charge after a load with the blip action?

 

May I suggest pulling the battery terminals off and cleaning them thoroughly? They can look, LOOK, perfectly good, and yet have corrosion built up, either on the lead terminals coming out of the battery, or down inside the wires attached to them's insulation. Down inside the insulation is the worst to find. Flexing the wire while measuring the wire's ohms end-to-end will usually tell the tale. Any doubt, it's easiest to replace the wire entirely.
Just a side note, if you use a regular lead-acid battery, it's a real good idea to put a piece of meltwall heat shrink on any wire connected to a battery terminal. It seals the wire against the acid mist that batteries put out.
Make SURE there are no wires connected to the battery before ohming anything. Even a slight voltage on a wire while ohming it will blow the fuse on the ohm side of the meter. Depending on the meter, it can be a royal PITA to get to for changing.

I also suggest checking all the ground points in the engine compartment. A corroded ground point, at either end of the wire, can cause all kinds of odd problems. It's not usually to tough to find them, or check the ends for corrosion.

Just my two little pennies worth...
Pat☺

 

Thank you for the reply and information. I spent considerable time doing just all that today (minus terminal cleaning) and all tested well with my multi meter. Didn't seem as bad today but driving it around still shows the same symptoms. I'll take a soft brass one to the battery connections, I did them just over two years ago but worth a shot. Going to swap out the alternator as well tomorrow and will report back.

 

Just an update. Cleaned up the terminals even though they did appear clean already. Also cleaned the alternator plug. After installing a new one it appears the problem has been solved but have not had time to test drive it yet. I will update in the coming days.

 

So here's the verdict:

Can't replicate the issue and voltmeter on my gauge pod would not drop below 14.0. However, once warmed up and revved the idle it drops to 450-500 and fights its way back up (recently set idle speed, replaced set screw o ring and cleaned the nasty port, also set timing with my usual two degree advance).

I cleaned my throttle body about a year and a half ago and still looks clean but never pulled it for a proper cleaning of the idle air control valve, which would be my guess. Would love to hear others input!