Idle jumps between shifts?

i'd love to know as well
my car has been doing it for about a year n a half now

I would start by cleaning the ISC and making sure the throttlebody and ISC are set to factory specs -- 1.5-2.5 turns from bottom on the ISC screw and 0.010 clearance on TB screw then a full turn in to slightly crack the TB open. Not a bad idea to look for vacuum leaks as well.

Wes

I would replace your IAC valve then try resetting your idle with the following procedure. It is the actual procedure for getting the measurements listed above. If your idle problem is NOT being caused by a bad part or vacuum leak then I have never seen this not fix the problem!

Begin with a cold vehicle. The idea here is to get the car to a firm cold idle with enough air bleed capacity left in the idle circuit for IAC adjustment.

The idle stop should be set first. Back out the idle stop screw, away from the bell crank arm, until about 1/2 turn past the point where it no longer makes contact (blade fully closed). Using a 0.010" feeler gauge, tighten until gauge just drags between screw and bell crank arm. Remove feeler gauge. Tighten screw exactly 1 1/2 turns. If the screw is very loose, put a drop of loc-tite or silicone on it, so it doesn't work out of adjustment.

Now remove the connector to the Idle Air Controller (IAC) just on the other side of the throttle body. Start the car and allow vehicle to warm for 2 minutes. Give a small "blip" to let it settle. If it is having a hard time staying running you may have to get an assistant until you can get to the front of the car. Now open or close the air bleed screw (CCW opens) next to the IAC until the car idles at 575 to 600 rpm. For guys with aftermarket cams and an EEC tuner, you might want to idle a bit more briskly, say 650 to 675.

Obviously, this rpm range is by what the car and driver wants...IE, no set idle speed, whatever works for YOU.

Turn off the car. Now count the number of turns clockwise to close on the idle air bleed screw. If it falls between 1/2 and 2, it's okay, now reverse it out the same number of turns. Log the number somewhere in case you need it for the future. Reconnect the IAC. You are done.

If the air bleed screw is above 2 turns, it's a good idea to tighten the idle stop screw another 1/2 turn, and then repeat the idle setting. If it is below 1/2 turn, then loosen the idle stop screw by 1/4 to 1/2 a turn, and repeat the idle setting. Be sure to put another drop of silicone RTV on the stop screw if it was disturbed. Reconnect the IAC.

Now remember we adjusted the set screw on the throttle body. That means that the voltage reading from the TPS sensor has changed. It should read between .96 and .99 volts. Anything outside of that range will cause all sorts of issues including misfires and rough idle.

you will have to back probe the TPS connector. With the connector attached to the TPS stick a paper clip into the rubber boot on the connector where the top and middle wires go into the connector. The rubber is very flexible the paper clip will slide in between the rubber and the wire.

Set your multimeter to volts. Turn ignition to ON. Then place your multimeter leads on the metal pins. If it comes up as a negative that is okay as long as you are -.96 to -.99. If you get this reading then great you are done and hopefully your issues are gone. If not proceed to step 9

This is where and extra pair of hands come in handy. Using a large screw driver you will need to loosen the bolts that hold the TPS. DO NOT USE A SCREWDRIVER THAT IS TOO SMALL BECAUSE YOU WILL STRIP THE BOLTS. They probably will be really tight so you have to really lean on the screwdriver and use some finesse.

Once the bolts are loose you will need to move the TPS up or down and continue to read the voltage. Once you get it to the desired setting you can retighten the bolts. What I do is I find .97 and then as carefully as possible I tighten the TPS down. what will happen is the voltage will change usually to .96 or .98 but that it okay. Once you are done with this manually open the throttle body a few times and close it then reread the voltage and make sure it is still within our desired range.

Depending upon how loose your set screw was you might want to cover it in RTV to hold your setting. At this point you have CORRECTLY reset you idle.

Great reset procedure, one small adjustment...

You can safely skip this section - as long as your TPS is within 0.48v-1.22v you are within the range that the computer will use as a "closed throttle" reference when the car is running. Anything outside of this range will set a code.

Wes

R.J. said:

Now remember we adjusted the set screw on the throttle body. That means that the voltage reading from the TPS sensor has changed. It should read between .96 and .99 volts. Anything outside of that range will cause all sorts of issues including misfires and rough idle.

you will have to back probe the TPS connector. With the connector attached to the TPS stick a paper clip into the rubber boot on the connector where the top and middle wires go into the connector. The rubber is very flexible the paper clip will slide in between the rubber and the wire.

Set your multimeter to volts. Turn ignition to ON. Then place your multimeter leads on the metal pins. If it comes up as a negative that is okay as long as you are -.96 to -.99. If you get this reading then great you are done and hopefully your issues are gone. If not proceed to step 9

This is where and extra pair of hands come in handy. Using a large screw driver you will need to loosen the bolts that hold the TPS. DO NOT USE A SCREWDRIVER THAT IS TOO SMALL BECAUSE YOU WILL STRIP THE BOLTS. They probably will be really tight so you have to really lean on the screwdriver and use some finesse.

Once the bolts are loose you will need to move the TPS up or down and continue to read the voltage. Once you get it to the desired setting you can retighten the bolts. What I do is I find .97 and then as carefully as possible I tighten the TPS down. what will happen is the voltage will change usually to .96 or .98 but that it okay. Once you are done with this manually open the throttle body a few times and close it then reread the voltage and make sure it is still within our desired range.

Click to expand...

Stanger007 said:

I would start by cleaning the ISC and making sure the throttlebody and ISC are set to factory specs -- 1.5-2.5 turns from bottom on the ISC screw and 0.010 clearance on TB screw then a full turn in to slightly crack the TB open. Not a bad idea to look for vacuum leaks as well.

Wes

Click to expand...

should idle be adjusted when warm ?

i have a 850 rpm set through sct chip ,
i am chasing this hanging idle lately

i had adjusted the idle one day ,car was warm ...and the nevt day it was much to low at start up

how does one clean the isc?
whats the best way to find vacuum leaks?

Most SCT dealers will properly setup your ISC and TB screws for you. If the idle has been getting worse lately but was good prior, I'd look at cleaning or replacing the ISC valve. I've sprayed electronics cleaner inside of it after removing it from the car. Swish it around a bit then let it air dry.

If you've got someone around you that can swap you their ISC, that would be a good, inexpensive place to start.

For vacuum leaks, you can trace each vacuum line and visually check the lines or listen for a hissing while the car is running. Some like to spray carb cleaner around to see if the idle changes but I think I quick visual/ear check would set you straight. Especially look at the PCV valve area behind the intake.

Good luck,
Wes