Low stumbling idle when at operating temp (like at traffic light)

[89FourRunner]

Hey all,

I have been running into a problem that grows larger as time goes on.

My 4runner seems to have developed a low idle (almost to the point of stalling) when the engine is at operating temps.

Example 1: After driving for a while - when I go to a red light and sit in neutral the engine rpms bounce from 500 to -350rpm, and while it bounces, each time it drops to 350 the truck obviously nearly stalls. I hold the gas a bit and sometimes it will clear up, sometimes it wont.

Example 2: I drove around to whatever destination, turned the car off and when I go to start the car to drive it again once I return, it will do the same problem as described in example 1. (as long as it is still warmed up)

This only happens at operating temp, never when cold.

It used to only occur with example 2, but now it happens like example 1 all the time, so it has progressed.


Any idea where I should start?

 

[flyinhawaiian01]

Any codes from the ecu? 4 or 6 cylinder?

When was the last time maintenance was done,ie., cap, rotor, air filter, timing, plugs, oil, filter, pcv valve?

Sounds like it needs a good tune up and idle needs to be reset. I'd also clean the throttle body while I'm doing all the other items.

 

[89FourRunner]

It is a 3VZE 3.0 V6 with 350,275 miles on it. I cannot tell you the last time it was tuned up, but I have done repairs down the line. Always ran well until this.

Did timing belt in 2013 along with water pump, thermo gasket, etc.

PCV valve is two years old, that was fun.

Oil and filter I do regularly, I just did it.

Air filter 6 months ago.

Fuel rail pressure damper a year ago.

I am sure it could need plugs, wires, cap etc - I cannot recall when it was last done in its 27 years. It just seems odd that sometimes it idles perfectly at 850rpm smooth, and more often then not it will idle like described.

 

[89FourRunner]

Im glad I made this post because It made me go out and take a closer look. All vacuum lines are good - cant find any intake leaks or anything obvious.

I DID find that my power interupt switch (on my negative battery cable line) had the negative battery terminal connected on it loosely, and I could pull it off with my hand, lots of wiggle room. I tightened that up and time will tell.

It would all make sense because lately Ive been feeling as though I had a weak battery or alternator as windows have been slower than normal.

Hope this is it.

 

[The Count]

Im glad I made this post because It made me go out and take a closer look. All vacuum lines are good - cant find any intake leaks or anything obvious.

I DID find that my power interupt switch (on my negative battery cable line) had the negative battery terminal connected on it loosely, and I could pull it off with my hand, lots of wiggle room. I tightened that up and time will tell.

It would all make sense because lately Ive been feeling as though I had a weak battery or alternator as windows have been slower than normal.

Hope this is it.

If that does not change the issue I would do the following:

-Disconnect battery
-clean throttle body very good
-reconnect battery
-set base timing
-set idle speed

And go from there. Worn ignition parts are never a "good" thing, but are unlikely to cause the kind of idle issue you are having. They will be beneficial for you to replace if they are so old you can't remember changing them, but I would focus on fixing the issue first. That way you don't accidentally do something wrong in the process of changing them and compound you problems, making it harder to diagnose the issues.

 

[Ahlem]

I had the same problem.
The timing was too advanced.
You do not say where you are located. In places that have real Winter, the temperature sensors have an effect.
I have had to adjust the idle speed seasonally.
We just replaced one temp sensor and until we get a good read on whether this solved the issue I'm just hoping.

 

[dogojoe96]

Pull your plugs! I had a very similar issue a few months ago and I was amazed they even barely still worked. If not they are a cheap part that will improve efficiency and by pulling them can give you more insight to your problem.

 

[89FourRunner]

The Count,

I have cleaned the throttle body and so far so good. It immediately boosted my RPM idle while cold and while hot.

I am not going to jump the gun and say it is fixed, but I did not experience the problem at all after the cleaning this morning.

I noticed the truck has a ton of blow-by, the intake passage had oil, the throttle body looked as though at one point it has a pool of oil at its base, etc - but the engine has 350,000 original miles. The PCV is fairly new, I am going to chalk it up to wear and tear over 27 years. The throttle body wasn't all that bad, but I cleaned it out real good, sprayed it well in carb cleaner, and sprayed that little bypass passage well with carb cleaner and a straw.

Time will tell but I had a pretty strong idle of 900rpm when warmed up at a red light. I have my doubts so if this did not work, then next I will check plugs.

 

[89FourRunner]

A good throttle body cleaning did the trick. It idles at about 900rpm steady when warm now.

Thanks for all the suggestions!