Engine Idle pulsing randomly - head scratcher

[popageorgio]

I do not own this 4runner but i end up working on it a lot because it belongs to my girlfriend. She has a 1994 4runner with the v6 no 4wd automatic Tran. I have done the normal tune up stuff. New plugs, new wires, replaced starter, and... well i have done alot to keep it moving down the road. But recently when the engine is hot and sometimes when it is cold. The engine's idle speed starts to pulse while its in neutral/park from 1k rpm to 2.5k over and over and will not quit while the power is not applied to the tranny. When the truck is in gear it seems to idle fine... but probly because it just cant physically pulse while power is transferred to the wheels. Well i thought maybe a vacuum leak and yes the intake had a crack but i got a new intake with no leaks and i still get the pulsing. My other thought is that it may be an issue with the throttle position sensor. But im not sure if i want to replace it for 90$ if it may not be the issue. The engine light is also not on.

The engine idle speed does vary form time to time while driving then parking it can sit at 1.1k or 1.7k and sometimes 1.9k its pretty random. but the engine revving from 1k to 2.5k after its warm is also random but getting to be where i can count on it doing it after driving the vehicle for more then 10 mins.

Any help or thoughts would be appreciated. Im sure this isn't the only old 4runner with idle issues. =)

 

[popageorgio]

I have also checked all the vacuum hose on the intake and they seem pretty healthy. I sprayed a little carb fluid around the mass of the on the left side of the intake and i got no acceleration. I dont really know how to check the pcv valve but could that cause engine operation similar to my symptoms?

 

[Mr.pughe]

dont waste your money on that sensor.......mine is doing the same thing. and i have replaced the sensor and it did nothing.....i am stumped on this one. but if i figure it out ill let you know. the pcv valve is on the passenger side valve cover....its easy to replace if you dont get anything mixed up when disconnecting the lines on that side of intake manifold. But if your going to go thru that pain i would get your injectors checked out, then make sure the fuel pressure regulator screw hasnt backed out. Then replace the valve cover gaskets and then change the pcv. It took me like and hour and a half to do all that..im not a mechanic or anything.........and that did absolutely nothing to mine but make it worse.

 

[popageorgio]

Well thats a bummer. I know the head gaskets leak oil like they were made to do so but i have not built up the courage to tackle that one yet. The pcv valve may not be the issue since you had no luck.

I read some post about people having this issue because of cooling and heat problems but The AC doesnt have any noticeable issues and the heater works good too. Im not real sure on what to check out next.

 

[Moustache]

Check her coolant level. My V6 does the same exact thing when its low on coolant and seems to stop when i topped off the radiator and res.

 

[popageorgio]

That is interesting you say that because the first major thing to go out on this vehicle was the water pump. then about a year ago the engine was running hot quite often so i replaced the thermostat and refilled the coolant and everything seemed peachy but still getting the pulsing off and on.

later on after that the truck had a coolant leak in one of the hoses that is going to the intake. I did fix that as well and filled it backup and it seem to do the same thing after wards as well.

I guess what i am getting at is that the engine has had cooling issues in the past but i have been fixing them as they come. topped off the radiator last night so i will have to see what my GF says about the pulsing.

Any other ideas that may make this happen are appreciated and thanks for the info bud.

 

[Moustache]

To get mine to stop pulsing or surging This is what all i did. Keep in mind though that i am having a coolant leak and am now surging again, but it was solved up until i started losing fluid again.

-Replaced every vacuum line attached to the Throttle body, and intake.
-Removed the throttle body and cleaned with TB cleaner and tooth brush.
-filled the radiator and res.
-I then adjusted my idle speed down to 850.
1. allow engine to warm up
2. run at 2500 rpm in Park for 2 minutes
3. turn the idle screw clockwise to adjust the idle down
(this is supposed to be done with a hand held tach but i did this with the dash tach)
The idle adj. write-up can be found in the Haynes repair manual

This helped a TON with my surging right up until a started leaking coolant.

Hope this helps man

 

[B208]

I have no information that will help you other than I'm having a very similar problem. And I am sick of messing with it and i think i'm gunna take it to a professional. Mine started out running fine just was lacking general maintenance from the previous owner. So i replaced water pump, thermostat, water pump, radiator and timing belt. Still ran fine stopped all the leaks.... So did a tune up. Replaced the cap and rotor, wires and plugs, also a k&n air filter. Then the pulsing started just softly noticeable at first only at low rpm's then after a week or so it became much harder shaking the truck while driving. I checked my plugs and wires making sure i did nothing wrong. Then i started reading on this forum. I found my way to the TPS and tested mine with an multi meter, it seemed to be a little out of whack. SO i replaced it at the auto parts store not knowing it needed to be clocked to work.... haha i was not able to get it home under its own power... Have now spent hours learning about the TPS and how to properly install one. However no luck in fact it is so much worse now. It will idle fine warm up fine but if you even touch the throttle it misses makes small pops and back fires. All said I'm lost and annoyed i spent 90 bucks on a tps 15 on a cheap mulit meter and then 50 on a better meter.


Ill let you know if i happen to figure out whats going on with mine or what the Pro says.

So you know mine is a 90' v6 3.o with a standard

 

[DoctorJest]

We had this problem on our '95 -- not sure if it'll apply to the older models, but the fix for ours was to do with the air-intake baffle. We had that replaced, and the problem hasn't come back since.

 

[lancakyl]

I have a question about your problem. Does it idle that way when the engine is cold and hot, only cold, or only hot?
Does it seem to be a particular type of driving, like city verses highway?

I'm having a similar problem, but it's intermitten.

 

[lancakyl]

We had this problem on our '95 -- not sure if it'll apply to the older models, but the fix for ours was to do with the air-intake baffle. We had that replaced, and the problem hasn't come back since.

Could you explain a little bit more? Do you know exactly what they replaced? I'm not familiar with what a baffle is specifically.
I've heard of dirty throttle bodies causing this.

 

[B208]

Could you explain a little bit more? Do you know exactly what they replaced? I'm not familiar with what a baffle is specifically.
I've heard of dirty throttle bodies causing this.

I'm not exactly sure what baffle he replaced, I think it might have been a electronically controlled valve in the top of your air cleaner box. I think it has something to do with the emissions. If you take off the outlet hose of the air cleaner box you can see it in there. I got a hole new "used" top half of a box from a junk yard and put on mine. It did not help resolve the issue.

 

[lancakyl]

It has to be a sensor. I just can't see those valves failing in there. They're all so simple. Has anyone tried the O2 sensors? I just bought one of them, and I'm going to replace it.

I also find that when I put the 4Runner into gear, out of park, the idle varies much more greatly, sometimes killing it. This is so bizarre, and seems to be so common. Oh well, going down the list is sure to fix it. Next I'm going to replace the sensor, I need to be the other one since there are two sensors, and clean my throttle body.

 

[Charlie_Hustle]

My truck just started doing this also on xmas day. The pulse is about 200/300k. It seems to do this when truck is already warmed up and not from a cold start.

 

[lancakyl]

Something I noticed the other day. I drove to the top of Mount Ranier in Washington state, and it idled perfectly at the top. Usually I am at sea level- I live on an island. I'm curious if we have a air pressure sensor of some sort...
I'm about to go and replace my upstream O2 sensor. Will keep you all informed.

 

[m3elmo]

not sure if it applies, but mine did this too, would go from 800rpm then up to about 1100, and then maybe drop down. i couldn't figure it out myself until the head gasket blew. The car always had some sort of coolant problem that seemed to slowly leak, then got worse. Not sure if this is your problem, but having coolant problems seems to do this.

 

[924runnerSR5]

hi guys. my v6 5speed has done the same thing 2 times. and the reason for it i think is because my coolant was low both times. when i added more it stopped right away. hope this helped you guys!

 

[lancakyl]

not sure if it applies, but mine did this too, would go from 800rpm then up to about 1100, and then maybe drop down. i couldn't figure it out myself until the head gasket blew. The car always had some sort of coolant problem that seemed to slowly leak, then got worse. Not sure if this is your problem, but having coolant problems seems to do this.

Thanks for the heads up. The only thing is that my friend as a '94 with the V6 and it does the same thing, and his head gasket was replaced two weeks ago.

Does yours still do it?

 

[lancakyl]

hi guys. my v6 5speed has done the same thing 2 times. and the reason for it i think is because my coolant was low both times. when i added more it stopped right away. hope this helped you guys!

Surprisingly I've heard this solution a few times. I will make sure, but I am pretty sure my coolant is full whenever it does it. I take it you're talking about within the radiator itself, and not in the reservior?

 

[popageorgio]

On this 4runner i have been working on it seems when the engine gets to normal operating temperature it begins to surge. The idle also varies quite a bit when starting the motor and stopping it. One thing that puzzles me is that there is no engine light on. I might try to read some codes if there are any at all. If that fails i will take it to a shop and have them diagnose the issue for me.