Idle Setup (Cable Driven Throttle Body)
No aftermarket throttle body should be expected to work out of the box. Also, if you have a large cam and/or more displacement changes may be required of the stock throttle body. All GM vehicles with cable driven throttle bodies (not fly by wire) use what is called an IAC motor. This motor controls an air bypass in the throttle body, which basically controls your idle. For example, if your idle is low and needs to be raised the motor will open a valve and give the engine more air, which will allow the idle to come up. The IAC motor has a certain range it may operate in, officially its 0 – 2XX IAC counts. If the valve is closed completely it will be at 0 counts, open is 2XX.
You want to set your throttle body up so that you put your IAC motor in a good effective range so that it may catch any idle dips and trim high idles just like it does in a factory vehicle. To do this, open your scanner and look for IAC counts. With a fully warmed engine at idle in Drive we recommend 30-50 counts. If your IAC counts are not in this area adjust your throttle body until it is.
Increasing Closed Throttle Body Airflow
1. Enlarging the hole in the throttle body. – Preferred method but carefully go up in size.
2. Moving the throttle body stop position – Not ideal, often leads to TPS range issues. Requires TPS to be unplugged while adjustment and TPS minimum voltage to be reset in the ECM after adjustment. Idle is often not as consistent as cars with an appropriate sized hole.
Why is enlarging or drilling the preferred method? The throttle body stop exists to keep the blade from digging into the bore of the throttle body and getting stuck. Relying on the gap between the throttle body and blade is not a good idea. This clearance changes due to temperature and expansion. This area also will get fouled with carbon deposits over time. This clearance area is very sensitive to changes. The factory throttle body uses a bypass hole. I recommend you utilize one as well.
Also by changing the throttle stop you run the risk of the TPS not being in an allowable range. If needed this can be fixed by elongating the slots on the TPS. If the throttle body stop was changed you must double check to make sure the TPS % and voltage are in the appropriate range afterwards. 0.45v-0.79v closed and no more than 4.8v seems to work in most applications. TPS % MUST RETURN TO 0.00%. The computer calls the lowest voltage recorded 0% throttle. If you move the throttle body stop the new lowest TPS Voltage must be resaved.
The computer will not try to control idle if TPS % does not read 0.00%
Excessive spark advance which may cause damage might happen on some cars if TPS voltage exceeds 4.8v!
Our preferred method;
1. The engine should be tuned decently well. Too rich or lean will greatly effect this adjustment. We often save this adjustment until the fuel trims are +/- 10% and the wideband is reading near stoich
2. Ensure TPS % reads 0.00%. Observe IAC counts fully warmed up in gear for automatics, neutral for manuals. A/C and defrost is off.
3. If IAC counts are higher than 50 counts remove throttle body and open hole up by 1/32nd. You should never exceed a 1/4″ hole. Go up in size slowly, you cannot easily undo a hole that is too big.
4. After IAC counts are in range double check to make sure TPS voltage is 0.45v- 0.79v and TPS % is zero. If not, adjust TPS, reset ECM by disconnecting battery or performing a write entire.
Again, general procedure is this;
1. Engine tuned decently well at idle? TPS % reading 0.00% at idle? If so go to step 2.
2. Are IAC counts greater than 50 fully warmed up in gear for auto or neutral for manuals? If yes go to
3. If no go to step 5 3. Open hole in throttle body -OR- unplug TPS and open throttle body stop.
4. Go back to step 1.
5. Plug in TPS if unplugged. Verify TPS voltage is 0.45v- 0.79v. If not, elongate TPS mounting holes and clock sensor until it does. If yes go to step 6.
6. Ensure TPS % reads 0.00%. If not disconnect battery, pull ECM Battery fuse, or WRITE ENTIRE the ECM. If TPS % reads 0.00% go to step 7.
7. Ensure TPS voltage does not exceed 4.8v.
The computer will not try to control idle if TPS % does not read 0.00%!
Excessive spark advance which may cause damage might happen on some cars if TPS voltage exceeds 4.8v!
