Fluctuating idle 2.7 manual

I don't suppose your clutch is starting to slip on occasion? I was thinking...when at idle that could defiantly cause erratic idle because of engine breaking....

Sitting at a stop light...its in first, foot on the clutch...and it starts to slip a bit....that would make rpms drop some right?

 

Dude you need to stop worrying about this.. The pcm has control of the idle, the engine has never stalled from idling too low (like at a stop light), the check engine light is not on, there are no trouble codes, I assume you have never walked out the front door of your house to a dead battery yet. The battery/charging system warning light has not come on.

The idle is simply responding when you turn on electrical loads. This is normal..

These newer cars and trucks have "smarter" charging systems. If you don't have any electrical loads turned on (wipers, blower motor, headlights) there is very little resistance/magnetism being generated by the field in the alt windings (it is not being asked to do any work so the field backs off). The engine can spin freely and you won't feel it "struggling" at idle.

You turn on a few accessories, the pcm sees this and it starts to crank up the (magnetic)field in the alternator. Now the engine has to work (a little) harder to idle. It is going to hunt around a little as it looks for it's "happy place" to idle at. But it is not "struggling" it is "responding".. this is a good sign. If the engine were stalling when you turned loads on this would be reason to worry.

Bottom line, with no warning lights, no dead batteries in the morning, and no stalling at stoplights, you should just relax, let the truck do it's thing and just be glad you're driving a Tacoma!

On a side note, sometimes when a alternator is beginning to fail, they will start to make a whine (I hear it most on Hondas and Toyotas with denso alternators, so basically all of them..). The whine will get louder with more elec loads turned on and I can verify that the alt is the problem (even without a battery warning light) by reaching down and disconnecting the field connector with the engine running. The whine will come and go immediately as I plug and un-plug the connector.. just a little tip..

All that being said, 500 rpm seems a little low but it is not uncommon on an older rig to have some vibrations and a pretty low warm idle. Does it shake violently? It may just be the way the engine is going to behave. It's just a truck. Other more luxury platforms (mercedes, lexus,etc) go to great lengths to insulate the driver/cabin from drive train vibes but those cars cost more.. trucks are for working. The engineers have to strike a balance between utility and comfort and so sometimes little quirks (even though to us they can seem quite annoying) don't get the attention we think they should.

Good luck! Don't lose too much sleep over this one..

 

Thanks!

No clutch slip.

I know, it's a truck and I shouldn't expect it too behave like a luxury vehicle, and don't expect it too. This is my first Tacoma, but I'm use to driving a truck as a truck.

Hah! I like that, "happy place". I understand that when there is a load put on the electrical system that the engine idle will try to adjust accordingly. However, I would think that it would eventually settle at an appropriate rpm, much like when an AC compressor first kicks on, there's a change in idle to accommodate the new load. It doesn't settle, it keeps revving until I take the load off. I don't think that's normal, but I could be wrong and that's just what this Tacoma is going to do.

Should I expect it to settle out? If it's a constant electrical load being applied, I would think that the pcm should be able to find it's "happy place".

It's a noticeable shake in the truck, not quite violent, but it shakes the whole truck, repeatedly, and it's damn annoying.

There is a nice whine coming from the engine bay when the revving is occurring... Thanks for the tip on the field connector on the alternator!

 

There's a whine! Pull the plug on the alt and see if the whine comes and goes

 

Disconnect the negative battery cable while the truck is running, if it shuts off then the alternator is bad, if it doesn't shut off then the alternator is still charging like it should...

 

No, don't do that

 

Why not?

 

That's a good way to kill the PCM seen it a time or two from techs that are being lazy.

 

That wine could be from the alternator, 2.7L aren't know for alternators going bad. I use a stethoscope but a long metal screw driver works check all your idlers and pulleys as well doesn't hurt. If you had a 4.0 i would suspect a bad alternator we stock them at work they like to lock up.

 

Pulled the field connector plug while the engine was hunting for it's "happy place"... Whine while plugged in, no whine while unplugged!

Good sign the alternator/voltage regulator is beginning to fail?

 

The alt is bad.. replace it

 

Thanks! Will do and we'll see what happens.

 

Replaced the alternator this evening with a Denso remanufactured. No whine and no fluctuations, solid idle when any or all accessories are putting a load on the electrical system. Thanks to all that helped!

I'll chalk the other replaced parts up to preventative maintenance on the engine...

 

I am currently having the EXACT same situation you did. I have a new PCV valve, newer plugs, clean MAF, Clean TB, did the seafoam treatment, I cant find any vacuum leaks, I cant find a bad ground, always do an oil/filter change every 3k miles.

I recently (within the past 6 weeks) replaced my alternator since the original one was 205k miles and was starting to fail (battery light). I am starting to wonder if my new alternator is faulty.

Just to be sure, it was defiantly the alternator replacement that fixed your issue?

 

Did you replace with a new or "rebuilt" alternator.

Note: Most rebuilt alternators and starters are still junk.

 

It was probably a reman. I got a duralast from autozone with a lifetime warranty though so I’m not too worried if that is the issue.

 

I would start there.

I would also stick with Denso.

 

If I need to purchase one then I will but for now I’ll start with my free replacement and go from there

 

Yes, the alternator fixed my problems. It turns out it was not the alternator, but the voltage regulator that is associated with the alternator that was the problem. If I can remember correctly, you can't buy one without the other.

I agree with @Jimmyh, buy a good quality alternator as a replacement. The cheap rebuilds from the local auto part stores can be hit or miss with quality and longevity.

 

I really appreciate the information. I will be testing the alternator tonight. Will be replacing (again) if needed. Will report back with results for future readers with this issue.