ShadowClown

my car is ideling too high...althought it changes all the time. When i first start it in the morning it idles about 3500rpm untill it warms up, but then the idle never drops below 1500rpm at all even with a warm engine, somtimes it wont go below 2000rpm. should there be a screw in the BAC valve for ajusting the idle? i can see where a screw should be i think but im not sure if there is anythig in there, I cant see in there and if I put a screwdriver in there it wont grip anythig so im not sure if its got a screw or not. any ideas is there ment to be a screw in there for ajusting?? what type of screw is it?

SpeedRacer

No that is just a hole in the BAC...I think if you plug the whole with your thumb the idle is supposed to drop a tiny bit..Or if you unplug the BAC you should have the same results(this lets you know the BAC is working)...although if you are idling at 1500-2000 then the BAC probably isn't effecting your idle at all, so that won't work. What year/model is your car. On top of your throttle body there is an idle/air adjust screw...it may be covered by a rubber boot that pops off. Tighten it to lower your idle. See if that works for ya.

ShadowClown

its an '88 13b turbo....i couldnt see an ajusting screw, would it still be there on a turbo model or only on the N/A's? The car has always idled a bit high but im sure its gotten higher than it used too.

deadof_knight

the air mixture screw /resistor like the shop manuel shows you step by step .or have your tried this if its always been a lil high maybe someone else adjusted this before you got it and got it wrong or it was misadjusted at the factory and no one else caught on ?

SpeedRacer

hmmm...actually, turbo models might have an ajustment screw on the BAC? I'm not sure though, but I think I've heard that. There is also a idle/fuel mix adjuster on turbos that is right by the boost pressure sensor, which is a little black box by the passenger side strut tower. It has a vacuum line going into it...this screw supposedly leans and richens your fuel mixture at idle. You might want to check that as well.

Sniper_X

the BACs are different for Turbo and NON_Turbo.

Nippon used the same mold at the factory for both..
However on the turbo models, there is a Idle adjust screw in the tube/hole that you are referring to.

In the Non-turbo cars, there is just a tube with no screw.

get a haynes manual or better yet, a factory shop manual.

Adjust the idle using the procedure outlined in either book.
(dont forget the initial set wire!!!!!!)

thend check and adjus the TPS (throttle position sensor) and then remove the battery cable wait 2 minutes, then re attach.

Drive the car normally for two days to let it learn.

You can make small adjustments, but dont forget a length of wire to take with you for shorting the initial set wire if you adjust the idle screw!!!

Also check the dashpot, and thermowax..

the thermowax is the culprit 50% of the time.

Deathbots

I'm having the same problems with my idle. It seems to have coincided with the cooler mornings here in Illinois. I didn't think it was a problem, but the engine does continue to idle at 1500 or so even with the temperature sensor 1/4 way up. If i turn it off, later on in the day it sometimes idles back at 750. It's very annoying.

What is a dashpot? And what is thermowax?

Sniper_X

Dashpot:
A non-vaccum/ non-electrical sluggush springloaded "buffer" that keeps your throttle from slamming shut all at once when you let off the gas.

Press on the little white piston with your finger and it goes into the dashpot slowly, release it and it returns quickly.

Helps with smooth idle when extra vaccum is applied to the system when accessories are causing load.. (but not a whole lot of help, really)


Thermowax:
A wax filled part of the throttle that holds idle high when cold.

You see, there is coolant running through it, and when the engine is hot, the wax melts and its piston retracts into the body of the thermowax.

When the car is off, there is no intake vaccum and the piston returns to the extended position (via a spring that is overcome by vaccum when the engine is hot). This hold the throttle open.

then the wax cools, and hardens. freezing the piston in its extended state and this hold the throttle slightly open until the car warms up.

(Its like a choke on other cars)

Deathbots

that thermowax system is ingenius. Very interesting, thanks for the response!