Base Idle will not stay set

Have set it several times after messing it up once a long time ago. It will stay at the same idle, but not the one I set. After successive restarts of the engine and revving, after each rev the RPMs come back down (after already hot) and stay at a different RPM. Tried to set it to 750 and it comes down to 1100, rev it.... then 1300, .... rev it then 1400.... and rev over and over and it keeps coming back down to 1100 - 1400 rpm range. Also something weird - whenever I push the brake pedal successively the idle RPM changes within the range I said above. I know that my brake booster is probably broken, but don't know how this would have any bearing on the situation seeing as I've tried to reset base idle with the booster out of the picture and it still does the same thing I said above. I have a new IAC (ISC), new plugs, new wires, new vac lines, done a vac leak test or 2 and came up with nothing, etc.. What ya'll think?

Possibly an intake leak.

i'm having a similiar problem.

have you cleaned your throttle body recently? if so, brake cleaner should NOT get into the holes inside the throttle body next to the butterfly valve. this will harm the FIAV (fast air idle valve). this is what i think i've accidentally done.

the FIAV increases the idle to around 1500 rpm upon cold starts. when the engine coolant heats up flowing through the throttle body, it warms a ball of wax which will expand and block the passage of the FIAV. then the idle should decrease to normal.

i suspected my ISC was going bad, so i took it out for a cleaning and cleaned my throttle body. when reinstalling everything, i think i reinstalled the TPS a little out of spec.

the proper way to adjust the base idle speed is a little more than just adjusting the BISS screw. here's how to do it: http://www.3si.org/wiki/index.php/Idle_Speed_Adjustment

and here is how to set the TPS, and throttle body place to spec: http://www.3si.org/wiki/index.php/TPS_Throttle_Position_Sensor_Adjustment

i just picked up a feeler gauge yesterday. so when i get home from work later today, hopefully i'll have some motivation to set the TPS, and perhaps mess with my idle. though, it IS friday, and i think my motivation to work on cars will change to beer or a movie. so maybe this weekend i'll get around to it.

I have not cleaned the throttle body since 2002 at 120k miles. The car now has about 140k miles as its not been driven much at all since Aug 2005 when Hurricane Katrina hit. However ya know I shop cleaned it and I have no way of knowing how well they did it. It was one of the things to do on my list actually. I guess I should get it out of the way to eliminate it as a possibility.

Due to my problems setting the idle with the BISS all the way in on 2 tries out of 6 I'm wondering if it is indeed the FIAV because the book says thats what it is if you can't set the idle when the BISS is all the way inward. I need to go grab a can of SeaFoam and clean the TB tonight.

Beer and a movie sounds much better at this point. I do know how to set the idle right, but I'll give that link a whirl to see if I'm missing anything. Taking off the throttle body means getting a new gasket (ugg) which I don't have, but it needs to be done. I've wondered about the TPS since the idle returns to idle at a NON-base-idle speed after I rev the engine a few times. Are there any testing procedures to make sure the TPS is bad/good?

i'm having a similiar problem.

have you cleaned your throttle body recently? if so, brake cleaner should NOT get into the holes inside the throttle body next to the butterfly valve. this will harm the FIAV (fast air idle valve). this is what i think i've accidentally done.

the FIAV increases the idle to around 1500 rpm upon cold starts. when the engine coolant heats up flowing through the throttle body, it warms a ball of wax which will expand and block the passage of the FIAV. then the idle should decrease to normal.

i suspected my ISC was going bad, so i took it out for a cleaning and cleaned my throttle body. when reinstalling everything, i think i reinstalled the TPS a little out of spec.

the proper way to adjust the base idle speed is a little more than just adjusting the BISS screw. here's how to do it: http://www.3si.org/wiki/index.php/Idle_Speed_Adjustment

and here is how to set the TPS, and throttle body place to spec: http://www.3si.org/wiki/index.php/TPS_Throttle_Position_Sensor_Adjustment

i just picked up a feeler gauge yesterday. so when i get home from work later today, hopefully i'll have some motivation to set the TPS, and perhaps mess with my idle. though, it IS friday, and i think my motivation to work on cars will change to beer or a movie. so maybe this weekend i'll get around to it.

the links i provided talk about the TPS and setting base idle speed, correctly. its much more than ADJUSTING the idle with the BISS screw.

the throttle body gasket is metal (or at least it should be), so you won't need to replace it. don't let this worry prevent you from pulling the TB and cleaning/inspecting it.

so are you in/around NOLA? i may be spending a year there helping rebuild. your car didn't get flood damage, did it?

the links i provided talk about the TPS and setting base idle speed, correctly. its much more than ADJUSTING the idle with the BISS screw.

the throttle body gasket is metal (or at least it should be), so you won't need to replace it. don't let this worry prevent you from pulling the TB and cleaning/inspecting it.

so are you in/around NOLA? i may be spending a year there helping rebuild. your car didn't get flood damage, did it?

Yes, around NOLA, but not sure of my address at the moment. GF problems and was supposed to move in with her up North. If you are interested in my story you can see it here at my car club web site that I never got going after Katrina hit: http://www.no3s.com/MyKatrinaPerspective.htm - I wrote it very shortly after the storm. I'd intended on getting the club going as soon as my car is good enough to drive again, but thats been a lower priority ever since big K hit.

are you ProwlerGT on 3Si?

are you ProwlerGT on 3Si? It is I.

BUMP - Anyone?

The ECU has tested bad. This is a common problem when you can't figure anything else out after testing nearly EVERYTHING else. Common mostly on 1st gen and hybrid years 3S'.

Hybrids dont have the faulty cap issues. ;) Only 91-94 DSMs (speakin of which I need to check the Talons out LOL) and 91-93 3s's/

The ECU has tested bad. This is a common problem when you can't figure anything else out after testing nearly EVERYTHING else. Common mostly on 1st gen and hybrid years 3S'.

so if it TESTED bad, then please confirm its bad by pulling the ECU, removing the cover, and inspecting it for leaking capacitors and/or fried ISC drivers.

i ordered a used throttle body from a guy off 3si. it comes with the FIAV and ISC. i only wanted it for the FIAV, but since it comes with and ISC, kill 2 birds with one stone. i only hope (i guess there's no way to hope or TEST with these weird ISCs) its a good ISC. but for 60 shipped, i knew it was a good deal. basically, i cleaned my throttle body with brake cleaner, adn this is a no-no, since it got down into the holes leading to the FIAV. i'll let you know if this solves my idle problem.

so if it TESTED bad, then please confirm its bad by pulling the ECU, removing the cover, and inspecting it for leaking capacitors and/or fried ISC drivers.

I've already inspected the ECU and its not leaking anything from the CAPs. Turns out the ECU IS GOOD from further testing so far. A misprint in the service manual led me to believe it was bad before and I've also discovered at least 7 exposed wires (Oil pressure sending unit, TPS, and A/C radiator cooling fan) from the bends in them. I've repaired the wiring issues I've found so far. Found them from stepping through electrical tests in the service manual for the MFI components. Problem is still not resolved and I'm away from the car now for a few months.

Linebacker - Did your new throttle body and new FIAV fix your problem?

Linebacker - Did your new throttle body and new FIAV fix your problem?

i STILL haven't received it yet, 1.5 weeks later. i hope it does solve the problem. i saw my idle fluctuating again today at a stoplight.

Linebacker - Did your new throttle body and new FIAV fix your problem?


YES! the throttle body assembly arrived just yesterday. took 3 weeks for it to arrive b/c the guy forgot to ship it. so for $60 shipped i got a TT throttle body with FIAV, ISC, and TPS. dropped it in, and idle was perfect. i fine tuned the idle with the BISS screw b/c the screw from the TT TB was further in than my NA TB.

so it was either the FIAV or ISC. i'm leaning toward the ISC. oh well, problem fixed for 60 bucks, as opposed to buying a new ISC for $132.

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SearchErr...did you have any update on your progress? have you replaced the ISC yet?