Hello from a Newbie who needs some help already!

[billsheila]

Well I am the proud owner of a 1999 4Runner SR5, but with a problem that has spilled over from before I started ownership!! I am hoping I might get some help. When I first looked at the car the owner disclosed he had been having trouble with hesistation and CEL coming on. The rest of the truck looked fine so we agreed to a price subject to him fixing this issue. The saga began. Long story short he is into it for the following:

New O2 sensors (not sure if they were aftermarket or toyota)
that didn't work so
New MAF sensor
that didn't work so
New fuel pump

They said "its fixed" so I paid the guy for the truck and picked it up (He paid for all of the above :violin:. Not 20 minutes into my new ownership and I have the same problem. It isn't throwing a code or throwing the CEL light on (although it did this in the past and it was P0171 "Lean Bank 1" when the prior owner brought it to the shop).

I have searched this site for help with that problem and it seems like a variety of things it could be, anything from the above items that were changed (which were obviously wrong) to the ECM, injectors, temp sensor, Throttle position sensor?

The only way I can describe the symptom is to say that it seems to occur if the truck is sitting idling for a while. The idle then drops real low and it starts to run rough. Then when you go to accelerate it just dies...still running but engine is making some popping noises, no power it just crawls along....then if you keep the accelerator pushed and pump it a bit, it seems to break through the dead spot and clear itself up. It has happened a few times but when it isn't happening, truck seems AOK and again no new codes or CEL these last few times. Once you get through the rough spot it will seemingly run fine. So far for me anyway it seems to only do it after a fresh start.

QUESTION FOR THE EXPERTS ON THIS BOARD:
What should I try next?

I was thinking the temperature sensor, because this is listed on the P0171 code helper that I read and my theory is it seems to happen when it is sitting, then is started and warms up? If not that maybe the TPS next? These two bits seem easy enough to change, but I have no idea how to test or change an injector.

Mileage 110K. Any help would be very much appreciated.

Thanks. Newbie

 

[JT3HN86R]

Clean the throttle body. IAC if it has one.
Should repair the problem.

 

[lucky'99]

Clean the throttle body. IAC if it has one.
Should repair the problem.

Here is the link on how to clean the Throttle body.

Toyota 4Runner Highlander Throttle Body cleaning and O Gasket Mod

I used this as a guide when I did mine resently (I've never done it before, and it was really easy!)

Dont forget to disconnect the battery before you do this. Autozone has the TB cleaner for like 5 or 6 bucks.

 

[cj80cruiser]

Was anything welded on the truck? I had a truck before and my dad stick welded a bumper on the rear. My ECM was having a similiar issue as you describe. Just a thought.

 

[billsheila]

Thanks guys for the advice. Cleaning the TB sounds easy so I will start with that. The TPS is like a $50 part so that may be next.

No idea on the welding...do you think if the ECM was fried it would run at all?

Also, what is an IAC?...see I really am a newbie!

 

[NickF]

If, after all that, it still doesn't work, try grabbing some new injectors

 

[ChildrenOfBodom]

Thanks guys for the advice. Cleaning the TB sounds easy so I will start with that. The TPS is like a $50 part so that may be next.

No idea on the welding...do you think if the ECM was fried it would run at all?

Also, what is an IAC?...see I really am a newbie!

I noticed it's common for a TPS to break... I did mine too. My IAC (Idle Air control valve) broke once too.

 

[cj80cruiser]

Thanks guys for the advice. Cleaning the TB sounds easy so I will start with that. The TPS is like a $50 part so that may be next.

No idea on the welding...do you think if the ECM was fried it would run at all?

Also, what is an IAC?...see I really am a newbie!

Yes sir, it will still run and randomly do that crap...mine did it after i let it sit for awhile, like overnight. It didn't do it all the time but just sometimes. I would check all other parts first though as I imagine an ECM would be expensive for a 4runner.

 

[billsheila]

Problem Continues

Well today I started with the Throttle Body clean up, as you guys suggested. It was indeed pretty dirty, but that didn't fix the problem. It seems to run a little nicer, but then this intermittent rough idle, hesitation "dead zone" on acceleration (just off idle) started all over again. Then I tried the TPS, changed it for a new one from NAPA, still no luck.

I was going to change the Engine Temp Sensor but I suspect that one is OK because when stone cold it revs up higher and then comes down in steps just like I think it is supposed to...and this temp sensor controls that action, so I suspect it is OK.

I then stopped in to talk to my local mechanic. He tested the Idle Air Control thing by asking me to put on the A/C...it seemed to work as well. I asked him about the ECM/ECU and he said "I doubt it". So at this point I am unsure where to look next. Mechanic suggested "drive it for a while, sometimes the computer needs to relearn".

So that is where I am. Love the truck, just have to get to the bottom of this gremlin.

What about spark plugs? Probably not...once it gets off idle and past this dead spot...it seems to pull strong and is fine at speed.

Thanks for any further assistance and help thus far.

 

[koulee]

Pull the negative on the battery to reset code and when it comes on again after driving, pull codes to see if there is a new code or multiple codes being stored...

 

[billsheila]

Thanks Koulee. Through all of this it seems to seldom actually throw a code. The previous owner got a P0171 code "Lean Bank 1" but I think only once, yet this symptom consistently happens and no new code. I have read the toyota tech article on P0171 and other than checking injectors which I don't know how to do or checking/changing the whole main computer...I think everything on the list has been done.

Regading the IAC, do you know can this part fail "partially" meaning it with "hunt" for idle but not totally die? I have heard others with this part failing they can't hold an idle at all, car simply won't run at all down low.

 

[billsheila]

self bumping not allowed!

 

[billsheila]

Update

Ordered another ECU from salvage yard. Should get it in the next day or two and will give that a try. Problem continues, obviously, intermittent as hell and very frustrating!