Strange loping idle turns 4Runner into UFO

[Woody]

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.

Topic

[college man]

With the battery light flickering That tells me that your alternator is
not putting out the proper voltage. If its an aftermarket alternator that
most likely your problem. see if this link helps further.

http://www.ericthecarguy.com/faq/solving-automotive-electrical-problems

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

[Bill]

Looks to me like a voltage regulator problem and I believe the regulator is inside of the alternator on that vehicle.

[Glenn]

Well, my answer may be unconventional because of a prior experience. You will get no better/ more knowledgeable help from people like College Man and Wysetech. I had a similar issue once, including the lights dimming with the pulse. I discovered this was due to a vacuum leak. After it was addressed all these symptoms disappeared. I honestly cannot say why the lights dimming with the loping was part of the symptom. I can only theorize that alternator was not spinning sufficiently thus causing minor voltage fluctuations. Best of luck…

[Woody]

[quote=”tomatofarmer1″ post=121775]Well, my answer may be unconventional because of a prior experience. You will get no better/ more knowledgeable help from people like College Man and Wysetech. I had a similar issue once, including the lights dimming with the pulse. I discovered this was due to a vacuum leak. After it was addressed all these symptoms disappeared. I honestly cannot say why the lights dimming with the loping was part of the symptom. I can only theorize that alternator was not spinning sufficiently thus causing minor voltage fluctuations. Best of luck…[/quote]

Interesting! I saw a friend once hunt around for a vaccum leak by spraying carb cleaner (I think) around suspected areas.

I think that would be an interesting and inexpensive thing to try. I suppose if I find a leak, I should plug it and see if the idle flattens out?

[James O’Hara]

Both autozone and pepboys have been known to have issues with doa dead on arrival alternators. Once you find a good one from them though they work like a champ. I also agree with wysetech and collegeman though I would say just check the bolt tightness on the alternator and on the battery terminals first simple check and is someone is moving to fast or simply forgot you will have the same issues from a loose connection. If it is not that then ya bad alternator.

[Glenn]

Here you yo on the possible vacuum leak…I do recommend water in a spray bottle to be safe though…

[Woody]

[quote=”MDK22″ post=121785]Both autozone and pepboys have been known to have issues with doa dead on arrival alternators. Once you find a good one from them though they work like a champ. I also agree with wysetech and collegeman though I would say just check the bolt tightness on the alternator and on the battery terminals first simple check and is someone is moving to fast or simply forgot you will have the same issues from a loose connection. If it is not that then ya bad alternator.[/quote]

I checked the connections and they seemed tight.

I’m hoping if it’s the alternator, that AutoZone will uphold the lifetime warranty.

[Woody]

[quote=”tomatofarmer1″ post=121789]Here you yo on the possible vacuum leak…I do recommend water in a spray bottle to be safe though…[/quote]

Thanks, that’s what I saw my friend do.

[Woody]

[quote=”college man” post=121718]With the battery light flickering That tells me that your alternator is
not putting out the proper voltage. If its an aftermarket alternator that
most likely your problem. see if this link helps further.

http://www.ericthecarguy.com/faq/solving-automotive-electrical-problems

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues%5B/quote%5D

[quote=”wysetech” post=121723]Looks to me like a voltage regulator problem and I believe the regulator is inside of the alternator on that vehicle.[/quote]

I haven’t yet had a chance to check for vacuum leaks. I did however pick up a multimeter for $6 at Harbor Freight.

I tested the battery with the engine off and it read 12.5v. I then tested the alternator with the engine running and it was bouncing quite a bit. In the attached 10 second video it ran from about a low of 13.35v to a high of 14.16v.

Is that normal? I’ve never tested an alternator so I have now clue really if it should fluctuate nearly a volt at idle and so quickly. Seems like it’s pulsing in the same way as the lights.

Is this a good indication that either the alternator is screwy or that the voltage regulator is unable to regulate voltage properly?

[Glenn]

While everyone is rightly looking at the alternator, I haven’t heard anyone address the loping engine issue here. A bad alternator won’t cause this symptom to my knowledge. I’m just saying, as suggested previously you may heed to look beyond the alternator. You might have more than one thing going on..

[David]

look at the o2 connectors, had a 97 rodeo do this, both banks were hooked up backwards

[Woody]

[quote=”tomatofarmer1″ post=121938]While everyone is rightly looking at the alternator, I haven’t heard anyone address the loping engine issue here. A bad alternator won’t cause this symptom to my knowledge. I’m just saying, as suggested previously you may heed to look beyond the alternator. You might have more than one thing going on..[/quote]

The lope coincides with the battery light flashing (when it flashes) and the lights dimming. Could this be a case of what comes first—the chicken or the egg? Is the pulse causing the engine to lope or is the loping engine causing the pulse by temporarily slowing the alternator?

I haven’t the foggiest idea. I’ve yet to get a chance to check for vac leaks, but could this be the root cause or is that unlikely?

[Woody]

[quote=”IGS4Dragon8″ post=121941]look at the o2 connectors, had a 97 rodeo do this, both banks were hooked up backwards[/quote]

I’m not sure what O2 connectors you are referring to or where I would find them. But I’m willing to look into them if I can find them.

[Glenn]

Good analogy and question…sometimes for me, like others, a past similar experience can cloud objectivity. I think all the other post advice has been good here. It just sounds exactly like what my car did with the vacuum leak last year. It all cleared up when I addressed the problem. That might have been the chicken coming first… 🙂
Good luck… I’m confident you’ll track it down.

[Glenn]

I have an idea for you… If it’s not too much of a hassle, remove the serpentine belt(s) from the engine, thus disabling the alternator. Crank the engine for a few minutes and see if the loping occurs. You can do this for a few minutes without it hurting anything. I just wouldn’t do it for long and let the temperature rise. This may help you zero in on whether the loping is caused by the alternator or not…just a suggestion…

[Author]

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