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biss screw adjustment

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For everyone who doesn't have link, the general rule is to have it screwed all the way in, and do 2 full turns out. Again, this is a rough estimate, but pretty accurate.
 
Just make sure to make the adjustments slowly, monitor your progress, and after each adjustment let it settle in for a bit before making another.
X2 - mine would take 5-10minutes to show adjustments.
 
Without a scan tool its a matter of trial and error. Though 2 turns from closed should do it but that can change depending on boost leaks etc.

Give turning it a shot little by little and let the car adjust and check the idle, if its not where you want it to be keep tinkering with it.
 
Without a scan tool its a matter of trial and error. Though 2 turns from closed should do it but that can change depending on boost leaks etc.

Give turning it a shot little by little and let the car adjust and check the idle, if its not where you want it to be keep tinkering with it.

With AT transmission, do you do this in park or neutral?
 
Don't you have to ground a test plug to do this? I thought i remember doing that based on the write up in tech forum.
 
Don't you have to ground a test plug to do this? I thought i remember doing that based on the write up in tech forum.
You do that with a timing light, i've never heard of anyone doing that with a biss screw.
 
Now you've heard of it (after reading the link below, of course).
1G BISS Adjustment
Thanks, sorry for the misinformation! I've never ground my biss before and i've always had a perfect idle though. Donniekak has helped me a lot with DSMs and even him, i've never seen do that. Makes sense though how it works.
 
A lot of "interesting" replies in this thread.

For a 1G (since some 1G questions popped up):

To adjust the BISS properly, you need to lock the timing, ground the diagnostic port, and then adjust the BISS until your RPMs are around 750-800rpm (or whatever you have it set to via Link, chip, etc.). If you don't ground the diagnostic port, the ECU will see the BISS adjustment as a change in idle airflow and will attempt to use the ISC to compensate for it. Keep screwing the BISS, the ECU keeps adjusting the ISC with no apparent change in idle rpm...until it runs out of adjustment range.

The other alternative for ECMLink users (as Brian suggested) is to leave it ungrounded and adjust the BISS while watching ISCPosition, until it reads between 30 and 37 or so.

1G BISS Adjustment

For a 2G:

The concept is similar, but I'm not sure about how the OBD-II handles locking the ISC out of the loop. According to the VFAQ, it requires a scan tool, but I've never played with a 2G so I'll leave it at that. The ECMLink method should work the same on both though.

2G BISS Adjustment

EDIT:

Damn it Brian.... you ninja'd me with your one-liner. :p
 
I just make sure that I have zero Boost Leak and everything in good working order, and I just play with it until it gets to 750 rpm.

Other wise, I would go with the 2 full turns before close position.

This is not the proper method on a 2g & what your doing is basically taking a guess where the correct spot is. The BISS screw is not use to adjust the idle, its used to center the ISC in the middle of its travel range to allow it to have most control over your idle. A side effect of adjusting the BISS is it may change your idle rpm but this is not a proper way to set it or your idle.

Just turning it a certain amount of turns may get you in the ballpark if your TB is 100% stock & there are no leaks & you haven't made any changes to it (though not a precise way to set it). But if you've made any changes to your TB or have leaks, etc, this method is basically a guess.

If you want to set the BISS correctly on a 2g you need the scan tool or ecmLink.
 
Last edited by a moderator:
This is not the proper method on a 2g & what your doing is basically taking a guess where the correct spot is. The BISS screw is not use to adjust the idle, its used to center the ISC in the middle of its travel range to allow it to have most control over your idle. A side effect of adjusting the BISS is it may change your idle rpm but this is not a proper way to set it or your idle.

Just turning it a certain amount of turns may get you in the ballpark if your TB is 100% stock & there are no leaks & you haven't made any changes to it (though not a precise way to set it). But if you've made any changes to your TB or have leaks, etc, this method is basically a guess.

If you want to set the BISS correctly on a 2g you need the scan tool or ecmLink.

Any chance u know a link to a thread for making a boost leak tester?
 
Any chance u know a link to a thread for making a boost leak tester?

Ok. I understand you are anxious, but PLEASE start searching before cluttering the forums with these types of posts. There are probably hundreds of threads on it....a simple title search on "boost leak tester" in the bar a few inches up there ^^^ should give you all the info you need.
 
This is not the proper method on a 2g & what your doing is basically taking a guess where the correct spot is. The BISS screw is not use to adjust the idle, its used to center the ISC in the middle of its travel range to allow it to have most control over your idle. A side effect of adjusting the BISS is it may change your idle rpm but this is not a proper way to set it or your idle.

Just turning it a certain amount of turns may get you in the ballpark if your TB is 100% stock & there are no leaks & you haven't made any changes to it (though not a precise way to set it). But if you've made any changes to your TB or have leaks, etc, this method is basically a guess.

If you want to set the BISS correctly on a 2g you need the scan tool or ecmLink.

I know its an old thread but how do you adjust it if you have ditched the ISC motor?
 
I was looking around cause I am having a problem and I found this. I am constantly needing to adjust my BISS. my RPM drop to 500 and sometimes my car will just drop bellow that I die, but it I turn my BISS about 2 turns left, my idle gets healthy and steady again. It will last a couple of weeks and slowly close again and I would get that bad idle.
 
I know it's an old thread but I didn't want to start a new one.This may have been answered already but i have searched and can't find it. My throttle body is removed, and I was planning on replacing my BISS screw and o-ring (boost leak) while its out the vehicle. I keep reading that i need to ground terminal 1 of OBD port. Should i wait and replace the BISS until throttle body is back in vehicle or it wouldn't hurt it if it's out? Any feedback would be appreciated

-Abe

PS, I don't have a scan tool or link
 
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