hanging idle when coasting....

DemonGT · Jun 7, 2005

my car idles fine...but when i drive it...and im coming to a stop light...i push the clutch in and the RPM's hang at around 1500 then a moment before coming to a complete stop it will drop down?? or as soon as i come to a stop it drops? what could cause this? is this the TPS or IAB...i do have a ford idle plate behind the IAB...mabe ill try removing it..need suggestions

jerryD · Jun 7, 2005

i would guess you are describing the VSS(vehical speed sensor). there is no problem going on. it is suppose to keep the idle up a little to help with up and down shifts. with a stock motor many don't notice it. when you throw in a modded motor it becomes more noticeable.

D347643 · Jun 7, 2005

its prob the wrong thing to do but i disconnected my vss and it went away. idle never hung or anything.

speedytang · Jun 8, 2005

Everything was OK. The other reason it does this is so the idle does not fall and not recover from WOT and under a load and you push in the clutch and the rpms fall fast and can't recover and stalls.

DemonGT · Jun 8, 2005

but i mean...i was going down hill on a road so i just coasted for like four blocks down hill with the clutch in and it did this?? also..where is the VSS at? its on the tranny isnt it?

jerryD · Jun 8, 2005

the VSS is on the end of the speedo cable.

speedytang · Jun 8, 2005

The VSS does not know your going up or down a hill it just knows your rolling. VSS is on the transmission end of the speedo cable.

super302 · Jun 8, 2005

I had this EXACT same problem, i cleaned the MAF, TB and IAC (all with throttle body cleaner, used q-tip on MAF), problem fixed....all for $3

rio95 · Jun 8, 2005

Did you take the IAC out off when you cleaned it? Could you give a short descrition, b/c I am switching to a fox TB set-up, so I have no experience with fox IAC's.

rio95 · Jun 8, 2005

Also, the position screw can cause hanging idles. Try closing the blade a bit more if you can. That worked for me.

DemonGT · Jun 9, 2005

would carb cleaner work for the IAB

SilverFoxbody · Jun 9, 2005

VSS is not computerized or controling idle position on 5.0.

your IAC or TB need cleaning.

Wknd_Warrior · Jun 9, 2005

if you have the adjustable Idle plate behind the IAC, you don't even need the IAC plugged in. Then the RPMs will drop off without hanging... at any time.

DemonGT · Jun 9, 2005

hummm? yes i do have the idle adjustment plate behind the IAC...guess all i can do is try it unpluging it and see what happens

89MustangGX · Jun 9, 2005

SilverFoxbody said:
VSS is not computerized or controling idle position on 5.0.

your IAC or TB need cleaning.

On Mass Air cars it actually does have some effect.

I do agree though that the IAB or TB may need cleaning and is more likely the problem (if there is one).

jerryD · Jun 10, 2005

the effect of the VSS besides for the cruise control and other various EEC things is to keep the idle up, while the car is in motion. to test it, when car is idleing in the driveway, blip the throttle a few times, or even hold it at 1500, 2k for a couple of seconds. let off of it and then the rpm should then drop back down to whatever you have the idle set at. next, take it for a drive. just do a couple of 1-2 shifts,then push in the clutch or just put it in nuetral. the rpm should stay up above 1k. when you come to a stop, after a brief moment the idle will come back down. reason is the VSS is reading that the car has stopped, and thus not needing the extra rpm's, it goes back to idle mode. another test is go on the hiway or a long road and get speed up and then coast as long as you can/want. as long as the car is moving the idle is going to be a little high because the VSS is detecing motion. if you try to "blip" the throttle like in the carb car days of warming up a car, the idle will still be high. but when you come to a complete stop, then the idle will come back to normal. if this is what is happening, nothing is wrong and the VSS is doing it's job.

jerryD · Jun 10, 2005

check this place out. lots of info.

www.fordfuelinjection.com

and this

http://fordfuelinjection.com/index.php?p=33

HISSIN50 · Jun 10, 2005

Jerry and Adam are exactly right about the VSS and rolling idle.

DemonGT · Jun 10, 2005

what jerry said is what its doing..just seems to be keeping the RPM's alittle TO high...close to 1500rpm....what should it be hanging the rpms at? seems to me it was like...1100 or something...will try some carb cleaner on the IAC...

any other info on if i can unhook the IAC with the idle plate?

HISSIN50 · Jun 10, 2005

DemonGT said:
what jerry said is what its doing..just seems to be keeping the RPM's alittle TO high...close to 1500rpm....what should it be hanging the rpms at? seems to me it was like...1100 or something...will try some carb cleaner on the IAC...

any other info on if i can unhook the IAC with the idle plate?

It will depend upon mods, base idle setting, etc. 1000-1500 RPM rolling idle is right in the ballpark, IMHO.

If you have a vac leak, that can create a hanging idle too (I think someone mentioned that, but it bears repeating). good luck.

hanging idle when coasting....

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