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1G Throttle Body on 2G/IAC/CEL/Idle

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Xit40

15+ Year Contributor
264
2
Nov 23, 2004
Weedsport, New_York
Ok so I recently put a 1G Throttle Body on my 2G and have been having difficulties with the idle. I have the Back up service manual and have read how you need a scan tool to adjust the BISS screw to idle the car down. It so happens that my brother in law is an Auto mechanics teacher at a local college so I have free access to his scanner (thank god). So I went over there yesterday and got the TPS adjusted to like .1% which was close enuff for me which helped the car idle down some. After that he started adjusting the BISS screw. In the service manual it says start the car and run at idle with the vehicle in neutral, all accessories off, and coolant between 80-95 C; hook the scan tool up and select item number 30 of SCAN TOOL (MUT-II) Actuator test. Now my question is this: my brother in law insists when he hooks up the scan tool that it holds the IAC at base idle without selecting it as the manual says is this true or does he need to select something specific as the manual says? I think he's wrong and have tried to explain it to him, but would like someone else's experienced postion. So right now my car idles at about 950ish with the BISS screw almost all the way closed no surge or anything like that just nice smooth idle it's just kinda high. Also I've been over there twice and had it hooked up and after both times the CEL has come on with code P505 for the IAC. I believe this has something to do with the scan tool being hooked up because it has never come one before ever. This is the same IAC that as on my 2G Throttle body for months and months and I never had a problem with the idle on it. It was always about 800ish. So after having the code read the first time I thought it was kinda odd and cleared it to see if it would come back. I drove over 250 miles with no sign of another CEL but after returning to my brother in laws and having him hook it back up to his scan tool and playing with the BISS screw some more it came back on within 40 mins.
 
The problem you're having seems to be an excess amount of air(metered) is bypassing/getting by, the TB.
Ways that air bypass/get by your TB butterfly for 1g TB's:
1. Improper setting of the TB switch causing the throttle plate to not close all the way.
2. FIAV
3. ISC
5. BISS screw
6. PCV

If the BISS screw in all the way in and it's not dropping your idle, then air is is making it's way in some other way.

I would check these in this order:
1. Do you have the Throttle switch installed?
2. Check the ISC http://dmtalon.v8eaters.com/ISC.html Since your getting the code, I think this may be your problem

If it's not one of these, then we will go from here.
Good luck
 
Throttle switch is in and adjusted correctly. I made sure when I changed the throttle body that it closes all the way, changed the seals, and cleaned it. So that's all good. I'm pretty sure the IAC is good since I never had a problem with it on the 2G Throttle body, but I'll check it just to make sure. I think it may end up just being because it's sooo hot out like 95 here right now because after it cools down for a lil while it will idle at 750 to 800 with the screw most of the way closed without surging or stalling. Doesn't stall when driving or bog down either. Once it cools back down I'm gonna check the coils and see what I get. Thanx for the IAC check procedure.
 
Uncontrollable idle is usually a sign of a vac/boost leak very near the throttlebody. What color is your ISC?
 
Tallen said:
Uncontrollable idle is usually a sign of a vac/boost leak very near the throttlebody. What color is your ISC?
Boost leaks are always problems but a boost leak letting in unmetered air will cause a low idle(depending on how bad they are). Unfortunately he's experiencing a higher than normal idle with the BISS screw almost all the way in.

Xit40, here's a little more info about the BISS and SAS
http://www.vfaq.com/mods/BISS-2G.html
 
Ok tested the IAC and the resistance between pins is fine. It seems to be idling where it should now right about 750-800 after it warms up for a minute. I dunno the computers on these cars are to wacky for me. I guess since I just reset the computer the other day that it needed to build a base back up or something because it idles real nice now nice and smooth just like before I changed the throttle body. I'm not messing with that thing anymore now that it idles right. Thanx for the helpful info much appreciated.
 
I bet your post is exactly right about resetting the ECU. It definitely relearns the settings and re-adjusts itself :thumb:
Glad it's running good for you.
Good luck
 
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