what factors would cause my idle speed to race?

I've got my timing set at about 5 degree before TDC....

and now must times at stop lights, etc it runs around 1900 to 2100 rpms? then I can (with the clutch depressed) kick the throttle and it will drop to about 1000rpms. occassionally down around 700?

I've backed off of the throttle stop too but it doesn't help the incosistency?

 

Mine does this sometimes too. It doesn't lope, just races when I stop until I blip the throttle and then it calms down. I have never really thought much of it lol. We will see what some others have to say.

Rob

 

that's a good description.

Might also note that i have lubed the throttle plate/butterfly in the event that it was mechanically sticking. no luck.

mine also has miss at idle but that might be for another message...

 

and it's an 87 4runner, 4cyl, 5sp.

forgot to add the details above.

 

I have a 1995, and it does the thing. I HOPE OTHERS TUNE IN FOR THE PROBLEM.

 

Dang mine does too! It's like a little sputter every couple seconds.

Rob

 

yeah....it shakes almost like a 'chill'.... which would be cool if I had a huge cam or something...but to me it just means its not running perfect yet.

I've looked for a vacuum leak or break but nothing. I'm wondering if it might be running rich and 'loading up' with too much fuel and that causes the sputter when it tries to 'catch up'?

or maybe its leaned out and a little starved? but it sure runs great and pulls hard under a load? you'd think that it would surface then if it was one of those two conditions?

 

no suggestions?

 

Check your anti-freeze and fill if needed. Thats the problem with mine. A small leak so every once in a while I need to fill (in the process of fixing) Mines a hose leak. I'd check it. Check the cap not the resavore.

 

I too have the slight miss at idle.. ive thrown new plugs, wires, cap, rotor, cleaned the TB, cleaned the Mass airflow, new 02, new tps. ive started to live with it lol. im thinking it might be a dieing mass airflow.. or perhaps its the oil i burn (1 quart every week and a half or so)

 

low coolant causing a miss at idle?

please explain....

 

the computer relies on the coolant temp sensor located on the front of the intake to tell it when the vehicle is warm and then the ecm will change from warm up fuel-ign-idle preset values and start using the o2 sensor and others to calculate air fuel ratio. I'm sure I just lost you but the sensor doesn't measure air temp so no coolant on the sensor no reading. Coolant will spash up onto the sensor giving quite an rpm surge especially at idle. Keep coolant toped off and no leak no problem

 

My nissan does this.. I don't pay any attention to it though.

 

Is it surging up and down when your foot is on the brake? You may need to adjust the idle lower. Low coolant has caused surging in the past for me, but it was really low. Also, I think a vacuum hose leak will have the same issues.

 

mine did the eratic idle as well. I tried everything and eventually my fix was to unhook the little small coolant line that goes to the throttle body and blow air through it using an air compressor.

highway

 

here's two thing I've found.. I have been having the brake issue when you depress the idle, it drops down. So I know my idle is not adjusted correctly.. In addition, when I'm 4-wheeling I will press the peddle and it drops and then surges if I push more on the peddle.. So.. I took apart my throttle body and cleaned out hoses connecting to the Air Valve below the throttle body.. When I took of one of the hoses nothing came out.. i remembered coolant flows through this valve.. I starting poking a small plastic zip tie and found it was clogged and rust chunks were coming out.. after I was finished cleaning it was flowing nice and clean and leaking into my bucket.. Now I've had Idle issues for a awhile and after cleaning the throttle body, Air Valve and adjusting my TPS everything is running great.. even my timing is adjusting correctly.. These three items are crucial for proper operation.. hope this helps..

 

did you try turning down the idle screw?

 

Try something next time it's racing. Instead of blipping the throttle pedal, put your toe behind the pedal and give it pull. If that brings it down, then your throttle cable is hanging up. Mine did this right after I got done installing my rebuilt engine and it turned out that I'd just set the throttle cable too tight and it wasn't letting the butterfly close all that way. But since you probably haven't messed with that, it could be that the throttle cable is wearing out and not smooth, maybe the EFI dashpot on the TB is sticky (this is really common), etc. Easy to check anyway, before you start trying some of the other things. Low coolant, vacuum leak, EFI adjustments. Could be a lot of things, but easy to check the throttle cable and all that first.