v6 Idling rough at 500 rpm
 

my 91 toyota v6 is idling at about 500 and pretty rough for the past month. I had a blown head gasket couple months ago and had whole top end rebuilt new valve guides, seats etc. replaced knock sensor, plugs, wires, cap and rotor, water pump and timing belt. I know there is no idle adjustment on the v6. Its all in the computer i have checked all plug wires. the rough idle goes away if I bring rpm up to 800 where its supposed to be. do I have a sensor possibly shot? any suggestions thanks.

P.S. had toyota check new h/g by sniffing radiator the said its fine.

The idle adjusting screw is on the TB you can turn it with a regular screw driver.. mine was filled with gunk and couldn't even tell it was there at first =p


Edit: here's a link to a pic Corey posted in response to a thread I made asking about the idle screw http://pnw4runners.com/tech/V6_3.0_e...e_screw_V6.jpg

Check your TPS if its bad of out of adjustment it will cause that. Timing can also cause it. I am currently chasing down a simular problem.

Well the V6 is supposed to idle more like 750-800 IIRC so if it is idling at 500 im sure it would be a little rough.

how do you adjust the idle??????? turn all the way to right?

Clockwise=Idle DOWN, Counter-clockwise=Idle UP

If the idle doesn't change much with that screw, there's another issue to address. More on that if need be...

probaly, i bought this truck with most of all the tune up parts in a box!.....it starts then dies down immediately? injectors maybe?

If your having no luck with the idle adjustment screw, you may need to set the throttle stop screw. First, make sure you don't have the idle screw turned all the way down(clockwise)by backing it off(counter-clockwise) 'till it's about flush with the housing(throttle body) if it isn't there already. Then, here's a pic of what's next.
Attachment 172494
The trick is to have it set just far enough so the idle smooths out. Start by loosening the nut,then turning the allen head screw all the way out(throttle closed as far as possible). Engine SHOULD be running rough at that setting. Then slowly screw it in till the idle smooths out. You'll notice a point when it "jumps" from around 500-600 rpm and rough, to around 800(or higher)and smoother. Stop turning it in when you find the "sweet spot" there, don't go too far in. And don't forget to tighten the lock nut when your done.

What your adjusting is how far open the throttle plate(butterfly valve)will close when the accelerator is fully released. It needs to be open a little bit, but not too little or too much for the engine to run smoothly.

ohhh, thanks i do this sat...would a cloogged injector/s cause it to die down immediately? Like as soon as starts it boggs down to the end?

Yes, it/they could. Next on the checklist though would be the Engine Coolant Temp Sensor Circuit(1 on the list, really, 2 being the idle adjustment) then the Volume Air Flow Meter Circuit, then the injectors. If we go by the FSM troubleshoot list.

HERE: http://personal.utulsa.edu/~nathan-b...63troubles.pdf

The rest of the manual HERE: http://personal.utulsa.edu/~nathan-buchanan/93fsm/

Okay,thanks I appreciate the info! I guess ill go down the list....and one thing at a time.

Mine idles at like 300 RPM sometimes. It Idles high at start up until it is warm, then it dies down to below 500. I'm not quite sure what is wrong. Couldn't a vacuum leak cause this?

i'd check the tps. that's exactly what mine did...listen to mudhippy.

What the TPS? I VE heard about that!.....whats it do?

Maybe, but it would make the engine run rough too.

The Throttle Position Sensor.

It tells the ECM how far the throttle is open, it then uses that input to help calculate the proper injector timing.

The FSM only says to check the TPS circuit if your experiencing a "High Engine Idle Speed" condition on the Poor Idling troubleshoot list. It shouldn't cause any other idle issues than that.

mine does the same.. idles up in the 1000- 1500 range untill it warms up, then it stays steady at 600rpm without any stumble...

id try adjusting the tps as stated before...

600 rpm is too low for idle when warmed up. The specs for the 3VZE is 800 rpm +/- 50 rpm.

And I wouldn't go fiddlin' with the TPS untill you make sure all other things are eliminated. I haven't heard of them coming out of adjustment too often. It could be malfunctioning electronically though. Then you'll need a new one, if the circuits don't test good.

As I stated previously however, unless you can't get your idle low enough by all other means, don't worry about the TPS.

MAP sensor? Any vacuum leaks?

It does...it feels like it's missing a little bit.

Maybe after re-building the motor the mechanics did not re-adj your idle , was it like that before ? If not then maybe all you need to do is re-adj back to the 800-850 rpm and you will be fine .

The TPS can create a idle problem as well as performance problems (ie power and throttle response), it can be diagnosed without removing , it basically tells the ECM when your motor is in or out of idle circuit operation as well as controlling VAFM operation in respect to throttle plate opening .
This link will give you the testing proceedure for your TPS :
http://www.4crawler.com/4x4/CheapTri...PositionSensor
* do not loosen screws unless you are going to replace , if it tests good then leave it alone :) .
When my TPS went bad it caused power/acceleration issues and generally unstable/high idle as opposed to low idle.
The Throttle Stop Adj should not be a adj you would have to make unless the throttle plate is sticking in idle postition from wear and if you have that problem then it is best to remove and clean Throttle Body thoroughly before adj.ing the throttle stop , that is why the idle adj is there :) .
Also I had problems with a vacumn leak at the Idle adj screw - it had a o-ring on it to prevent vacumn loss from around it and by the threads of the srew , dealer could not order but I replaced with one out of generic plumbing repair o-ring kit , lubed with dielectric silicone and re-installed and it sealed well and had resistance when turned again from good airtight seal from new o-ring , but this vacumn leak resulted in idle creeping up after stopping , not a low idle condition .