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Idle Position Switch / Stop Switch cause high idle? How to TEST?

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tsi1991awd

10+ Year Contributor
1,366
6
Sep 28, 2008
Puyallup, Washington
How do you test the idle stop switch (located on the top of the throttle body)? I am having a weird idle issue now. Put the throttle body back on and when it warms up it will idle right around 800.

When I drive and come to a stop it will idle at about 1100 or 1200. If i hit the gas a bit it will go down to around normal. Other times if I just sit and wait, it will come down and start to idle normal (takes a minute or two)

So i am wondering if the switch is toast or out of adjustment or what? Anyone think this switch could be the problem?
 
The switch simply connects ground to the top terminal. With a multimeter, place one lead on the idle switch terminal and the other lead at chassis ground. If the switch is working properly, you should see low resistance (few ohms) when the throttle plate is closed. When the throttle plate is open, it should go high resistance.

There is a very specific procedure for setting the idle switch in the manual if you have access to that. If not, I can look it up when I get home.
 
The switch simply connects ground to the top terminal. With a multimeter, place one lead on the idle switch terminal and the other lead at chassis ground. If the switch is working properly, you should see low resistance (few ohms) when the throttle plate is closed. When the throttle plate is open, it should go high resistance.

There is a very specific procedure for setting the idle switch in the manual if you have access to that. If not, I can look it up when I get home.

Would a bad switch cause that high/weird idle? Also, is there any voltage from the ISS wire (green wire) that i should check for? I also do not have the manual.
 
Not having the idle switch working could do some weird things to the idle. It's definitely possible.

There's no specific voltage to check for on the switch. If the switch terminal is connecting to ground when the throttle plate is closed, it's working.

I didn't get a chance to look up the procedure for you last night. I can do it tonight, though. Sorry about that.
 
To adjust the switch. You unloosen the lock nut of the switch, turn it all the way out counterclockwise. Make sure you loosen up the throttle cable as well. Get you meter put on a good ground and the positive on the switch, turn switch in unitil you get continuity, when it is constant;turn the switch 15/16 of a turn clockwise, stop and tighten up the lock nut and your done. Make sure you tighten your throttle cable.
 
^^^ Thanks, I couldn't remember the amount you turn after getting continuity and I didn't want to get it wrong by guessing.
 
Everybody should have a copy of the factory manuals. Go get them.
http://www.dsmtuners.com/forums/fre...tions/344490-download-1g-service-manuals.html

The ECU pulls the IPS signal high and looks to see if it's high or low to know if the throttle is closed. IIRC the pullup voltage differs between the 90 and 91+ ECUs. With the connector attached and the ignition on you should see close to 0v with the throttle closed and something like 5v or 12v with it open a little bit.

Getting a good idle can be tricky, Just scrubbing the factory sealer off the back of the throttle butterfly is enough to cause an air leak that won't let the idle down. What I'm trying to say is it doesn't take much extra air getting in to cause a high idle.
 
Also, make sure that your throttle body is grounded to either the IM, the black cast brace that connects the IM to the head, or to the firewall. Most people overlook this when they take the car appart, and put it back together. There is usually a small piece of wire that connects the throttle body to the chassis or block, otherwise that ground the circuit completes when the throttle plate is closed, is NOT the same ground reference as the ECU as its floating. Especially if you run a phenolic TB gasket and removed the cast black brace. :p
 
Thanks for posting the procedure. I will have to check it out on Sunday when I am off of work.

The only thing is when the tb isnt connected to the cable or anything the plate moves freely. Every once in a while it will stick (can feel it when pushing the gas to accelerate)...can this be cause by the idle stop switch? I mean sticking CLOSED...when I go to push the gas its a bit tight/hard and then loosens up once the plate opens...at least i think thats whats happening.

And ONE MORE important thing...happened a lot last night and this morning. Coming to a stop, push the clutch in put it in neutral....idle falls to 500 then up to 750/800 then goes down a tiny bit to maybe 650/700 then back up to settle. What can make it do that? Think its a bad IAC motor? I put in a bypass plate for the FIAV....is there any way to know that the IAC is bad or would this not be the cause?

Good point. That's usually my second post when 1G people are having IPS problems.

I have the little L shaped bracket that screws into the top and goes through the top tb bolt hole. I am missing the NUT for the big bracket that connects to the engine. (The one that the 2 TB bolts go through that connects to the side of the engine)....anyone know the size of the nut? Could that be a problem?


ONE more thing. At a stop with the AC button pushed (so the fan is on), my idle is at 1500 and wont go down. This morning it was surging. 1100 to 1500. When I turn the fan off, idle goes back to normal. Didnt do this before
 
Just want to say thanks for all your help. I went out today and checked the resistance on the idle stop switch. It read 10.3 I thought that was ridiculous after reading how you're supposed to adjust it! So I took the switch completely out and unbolted the throttle cable from the manifold. There was quite a bit of slack in the throttle cable to begin with.

So I made sure the throttle was closed all the way, began to screw in the switch and got to the contact point. I stopped. It read .2 on my multimeter. So I went ahead and screwed it in 15/16 of a turn and tightened the lock nut, resistance is now .6

Now, .6 and 10.3 are COMPLETELY opposite ends of the spectrum!! I tightened the throttle cable back up, leaving a bit of slack. Started car...idled fine. Drove and WOW, my gas pedal used to be real loose and I could push it down a bit before it would even do anything. Now there's no play and feels really nice! Came to a stop and it idled fine. Ran it down the road and back...idled fine. Amazing what two small adjustments can do! Thanks again for your help!
 
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