IDLE acting all kinds of crazy whacked out!

[4x4runner91]

Well, I've tried searching this and other forums/sites, but I can't seem to get enough info to figure this problem out. 1990 4runner V6 3.0 4x4: I have an Idle with a mind of it's own! At any random time, it will drop from about 900-800 to about 500...(it kinda jumps/hops around 500 like its bogging down and gonna shut-off but never does.) Sometimes when Im driving, it idles perfectly at 800rpm or a little lower. At night, the lights get dimmer till I start driving again. I've replaced the fuel filter, used SeaFoam and various other injector cleaners. I haven't touched the Idel screw yet, because Im curious as to why it idles at normal speed sometimes. Could this be "Air/Fuel" related or is it just something bizarre? I've only had the truck a year and haven't messed with anything electrical except a new battery. I am going to replace the spark plugs soon, regardless if that is the problem or not. If anyone has anything else that they think I could check, It would be much appreciated. Thanks in advance.

 

[RedApe]

We have a 94 SR5 that JUST started doing this as well.

First first guess, and part to replace: TPS
Throttle Position Sensor. A malfunctioning TPS will do all kinds of weird stuff...at idle or otherwise.
Check on that first.

 

[ultrabongo]

There's lots of stuff to check BEFORE the TPS- fuel pressure, injector seals, electrical ground points for all injection components, electrical connections for same, intake hose leaks, pressure regulator, injector spray patterns.
The TPS does create wierd symptoms, but usually more like a flat spot- the engine will "hunt" but its not just an idle problem. The dim lights are an indication you are idling below a level at which the alternator puts out sufficient current to run the truck-
Adjust the idle screw last. Check all the other stuff first- ignition components, too.

 

[Kmvreter]

Look at your exhaust gas recirculation (EGR) valve or system. If it's stuck partially open from being carboned up then hot exhaust is feeding back in when it shouldn't at idle. This will drop your idle, make it sporadic and want to die as you describe, but still run OK at off idle rpm's.

 

[4x4runner91]

EGR

Look at your exhaust gas recirculation (EGR) valve or system. If it's stuck partially open from being carboned up then hot exhaust is feeding back in when it shouldn't at idle. This will drop your idle, make it sporadic and want to die as you describe, but still run OK at off idle rpm's.

EGR- Is there a way to clean that? Some SeaFom maybe...for the carbon?

 

[88turborunner]

IAC (idle air control valve) will make this happen. also your right the tps could be the problem. check the fsm and perform a ohms check on it. should be from like a 5k-10k ohms variating resitance depending on your throttle posistion.
IAC valve sounds more like it though. it has a diaphram in it and it gets a little loose when you have gotten the engine compartment heated up causing it to work correctly.
just a theory though.
check the fsm to see how to properly isolate and check the valve.

 

[88turborunner]

some brake cleaner would work fine to clean up any carbon. its a dry cleaning solvent so no residue is left.

 

[MtnManx3]

IAC (idle air control valve) will make this happen. also your right the tps could be the problem. check the fsm and perform a ohms check on it. should be from like a 5k-10k ohms variating resitance depending on your throttle posistion.
IAC valve sounds more like it though. it has a diaphram in it and it gets a little loose when you have gotten the engine compartment heated up causing it to work correctly.
just a theory though.
check the fsm to see how to properly isolate and check the valve.

I have a 94 that I have been struggling with a high idle.....IAC is what several people say, but where is it? There is a coolant in/out underneath the throttle body and the vacuum lines on top....other than the dashpots on each side, there is the TPS, but I see no replaceable IAC.....

 

[88turborunner]

http://www.toyotanation.com/forum/showthread.php?t=86540

google is your friend when trying to find things.

peace,
Chris

 

[88turborunner]

my bad about the tps resistance if some were thinking, what a **** thats not the right resistance numbers.
so when checking a tps verify it with the fsm, which gives you a table of numbers.

 

[88turborunner]

http://www.toyotanation.com/forum/showthread.php?t=86540

google is your friend when trying to find things.

peace,
Chris

 

[MtnManx3]

http://www.toyotanation.com/forum/showthread.php?t=86540

google is your friend when trying to find things.

peace,
Chris

Roger, got it about the google.....but all the info I found when I googled was about a Camry also. Still have not found one on my 94 4runner. I bought a separate throttle body, took it apart just to see with what I was dealing and didn't see any kind of air passage with a valve other than the throttle plate.

I would LOVE to see pics of one on a 3.0 in a truck or 4runner and not a Camry, so I could clean mine.