2g Bored Throttlebody/SAS Adjustment

[daren_p]

I have a question about adjusting the SAS & throttlebody adjustment in general, when installing a larger throttlebody. I recently installed a bored 2g TB, 60mm with the halfshaft mod so equal to 62.5mm. I believe I understand about setting the TPS, with the gap gauge & how you want the BISS screw adjust so the ISC is in its center of adjustment range but what effect does the SAS have & how do I know its set properly? I would think this will effect your idle rpm?

When I received the TB I read the method to adjust the SAS by backing of the SAS till the throttle plate is completely closed & then turn the SAS screw in 1 1/4 turns from this point to set it. Well when you back off the SAS screw the throttle plate actually rotates further past what I would call closed or completely perpendicular to airflow, so I measured the distance from the top & bottom of the throttle plate & when they were both equal I called this "closed" & adjusted 1 1/4 turns from there. This looked to be more backed off or closed compared to where it was origionally set & when I removed my stock unit it was also more open compared to this adjustment. So what I did is I took top & bottom throttle plate measurements from my stock TB & used them to set up the new TB, so I turned the SAS screw in further to open the throttle plate abit more & this ended up also being basically where the TB was adjusted at when I received it (don't know if it was correct or not).

Now I have got my new turbo install 100% finalized but when I started the car to check for leaks I noticed a much higher idle. It was sitting around 2200 even once the car was warmed up. I screwed the BISS all the way down just to see how much it would drop but it was still at around 1700. The ISC & TPS are off my old stock TB & were working correctly so I don't think these are an issue. I haven't had a chance to look at DSMLink to see what my values are saying but I'm thinking the SAS is adjusted to hold the throttleplate to far open & giving me the high idle. So do I need to readjust my SAS & is there a way to verify its adjusted correctly? I have tried to read up on my issue but haven't come across the same issue so far. I'm new to adjusting the TB, so any input would be great.

 

[romeen]

Daren, have you done a boost leak test to make sure it's not just a large vacuum leak causing the high idle? I am planning on sending my TB in to Steve soon. From talking to him I was under the impression that other than the BISS there really shouldn't be anything to adjust. He even suggested scribing a line to mark the orietation of the TPS so I can simply put it back on in the same position it was originally. Maybe I misunderstood him or I am missing something.

Do you think the ECU needs to relearn and adjust for the new airflow level?

 

[daren_p]

No haven't done a proper boost leak test, as I didn't want to test it all to find out I just have to take it back apart to pull the TB again. I know there were no boost leaks pre disassembly & I only removed two couplers. I made sure they were good & tight when I reinstalled them but yes your right there still could be a leak, which I do know could cause an idle issue. You are correct in your case as you will be sending him your TB for machining, I just bought one out right from him so I wouldn't have any down time. TPS & BISS adjustment don't seem to be hard & I believe I know how to set them up correctly.

I think you are correct in that the ecu sorta learns it idle after awhile but since I screwed the BISS all the way in & the idle is still a good amount high, Im thinking the ISC won't be able to adjust itself enough to get the idle in spec, unless I'm not understanding the correct TB operation. I couldn't find alot of info on adjusting the SAS & how you know its correct, so thats why I'm wondering about how mine is & should be adjusted.

 

[romeen]

Is the IAC on the new TB one of the older style ones with the metal casing and light tan colored connector housing for the electrical connector? If your original TB has one of the IAC's with an all plastic casing which is dark brown or black you might want to try swapping them. For some reason the older style IAC causes my car to idle a little higher even though both the IAC's I have test fine. This could be just an isolated incident in my case and I can't explain why it would do this but they are so easy to swap out that it may be worth a try if all else fails.

 

[daren_p]

Is the IAC on the new TB one of the older style ones with the metal casing and light tan colored connector housing for the electrical connector? If your original TB has one of the IAC's with an all plastic casing which is dark brown or black you might want to try swapping them. For some reason the older style IAC causes my car to idle a little higher even though both the IAC's I have test fine. This could be just an isolated incident in my case and I can't explain why it would do this but they are so easy to swap out that it may be worth a try if all else fails.

The ISC is the one with the lighter tan colour, I believe. The new TB didn't come with the sensors so I just swapped my old ISC to the machined TB. The ISC worked fine on my old TB so like I said, I doubt its an issue.

 

[daren_p]

Well I did a boost leak test, well sorta. The new tester wasn't sealing 100% but I was able to get 10-15 psi in the system & spray it all down & didn't come up with any leaks. I have the BISS adjusted all the way in & the idle is lower now, maybe 800-900 rpms. When I logged ISCposition & learnIdleAdj, they are both low still. As far as I understand this mean Im bypassing to much air past the throttle plate & need to turn the BISS in more to raise these values up. Well since I can't do that I have to look at other areas. Seems to be a couple things that could be causing my issue. The throttle plate can be letting to much air by so I will try adjusting the SAS to see if I can get a better seal/less airflow past the plate (then re-adjust the TPS & BISS as needed) If this doesn't help, it seems the FIAV can also be leaking allowing to much air to bypass or finally the plate may not have a tight enough fit. I have been told to use model paint around the throttle plate edges to help with the sealing & it appears they do this as well from the factory. One other thing to mention my throttle cable tension is fine & not holding the plate open abit.