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Recently I acquired a 1997 Toyota 4Runner 4wd Ltd V6 with 360k+ miles.
Engine runs and performs fine. However, when at idle, the engine lopes audibly; you can also feel the truck physically swaying just slightly with the idle change.
Visually, the tach gauge will move less than 100rpm. Pretty much an invisible rpm change when looking at the tach. My guess is maybe 75rpm change.
Occasionally the battery light will flash in conjunction with the loping idle. Usually only when the engine is cold, or the headlights are on while driving at night — but not always.
The lights, all of them except the aftermarket stereo I put in recently (this problem existed before the stereo was installed) pulse in time with the engine loping (see attached video).
While driving at night, I can see the dash lights pulsing as well as the headlights, and it does not matter what speed I am traveling. The pulsing headlights pulse at the same rate regardless of speed or engine rpm.
I can’t hear the loping idle while driving, but I always know by the dash/headlights lights at night and the ABS light during the day.
There is no CEL light either.
Occasionally, the pulsing will stop while I’m driving, then promptly start again when I step on the brakes, turn on the A/C or something similar.
As I understand it, the alternator was replaced a couple of years ago so I took the truck to the parts store for them to test the alternator and battery. They said the battery was fully charged and the alternator was working. The guy did say that the alternator was spiking up to 15.1volts.
I checked the ground wires that I could find, but admittedly I did not check every wire in the engine compartment. I made sure the battery terminals were tight and clean too.
This issue has been present since I acquired the truck a couple of months ago and It is quite annoying to constantly have the engine loping or headlights flashing like a UFO. But there doesn’t seem to be any performance issues related to it like stalling or loss of power.
I’m unsure if this is an electrical issue, an engine issue or something else.
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Unfortunately I couldn’t get the video to play. That said, I’m not convinced the alternator is the issue. I think it’s more of a symptom based on your description. If the idle gets low enough, it will turn the battery light on. That said, I would be looking to the cause of the ‘loping’. In this case, looking for vacuum leaks is probably a good idea as suggested, however, if you have an issue with your IAC then that could also cause the issue. It could also be the computer getting bad information and trying to correct for it with the IAC. I would think that would set a CEL.
In summary I think finding the source of the loping idle will solve all the issues you’re having.
Good luck and keep us posted on your progress.
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