Initial Set up of throttle blades and TPS

If you have done a conversion using a GM TBI system or modified the engine or it's just a high mileage engine and TBI unit these are some critical mechanical adjustments needed that the ECM can not perform. This information along with proper fuel pressure is critical before any tuning be done.

So three things mechanical need to be set before any data logging or tuning can be done so the ECM has proper functions within it's parameters to be efficient.
1. Fuel Pressure (stock is 9-13PSI) all the best running engines I have seen are at 13 PSI or more if engine is modified.
2. Base timing. This is set with EST bypass wire disconnected and usually set to 0. Modified engines like more. If you set for more than stock calls for it also needs to be changed in the chip so you don't end up with to much advance after the ECM adds more timing.
3. Setting Minimum Air on throttle blades. Some people call this idle and it would be on a carburetor engine. But an EFI engine idle is controlled by the ECM.

There has to be a little opening of the throttle blades to let in some air so fuel can pass the throttle blades at idle. If the blades are totally shut your engine will not idle well and you could experience a sticky throttle because the blades are totally closed, then the engine starts causing vacuum and it takes a great amount of force on the gas pedal to brake free. Not good.

So to set Min Air and then TPS here is the procedure below.
Idle Air Control

Take a paper clip and open it up and form it into a big "U" shape. Insert the clip ends into the ALDL port between the 'A' and 'B' pins.

Then turn on the ignition, but don't start the engine. Wait 30 seconds. Then remove the connector from the IAC.

Start the engine. You are now going to adjust "minimum air". There is a Torx screw on the side of the throttle body. This is what needs to be turned to adjust minimum air, or more commonly known as "idle speed". It comes from the factory with a protective metal cap over it. If the cap is still there, use a small punch or drill to knock it out. Set the idle speed to 100 rpm below idle setting in your chip, rotating the Torx screw clockwise to raise rpm, and counter-clockwise to lower rpm. Once the idle rpm is set, turn the engine off.

Re-connect the connector onto the IAC. Start engine. Idle speed is now once again governed by the ECM, and once warmed up should be at or very close to idle speed in the chip.Idle should be smooth and steady.

If you set an SES light by having the IAC disconnected, turn the engine off and remove the battery negative terminal for at least one minute. minutes. This will clear the ECM of all trouble codes. Re-connect the battery and drive the car for 20 minutes to allow the ECM to relearn your driving style.

Throttle Position Switch (TPS) Since we moved the throttle blades we also moved the TPS and it may need to be reset. Check the reading with key on engine off with either a scan tool, laptop with your choice of tuning software or a digital voltage meter.

Read the TPS voltage. It should be 0.54Volts +/- a little.

If out of spec, loosen the two screws holding the TPS to the throttle body, and slightly rotate the TPS up or down, reading the voltage until it comes into specification. Sometimes you need to file out these holes to get enough room to move the TPS or bend the tang inside that rests on the throttle shaft. Tighten screws. Recheck voltage. While we are here lets check the TPS for proper operation. Using the throttle lever, rotate the throttle to WOT (wide open throttle). The TPS voltage should be over 4.0 volts. Close the throttle again, and then slowly open it to WOT, observing the voltage reading. It should increase progressively and in a linear fashion. If it sticks or jumps or falls off at all while doing this check, that could mean a bad TPS switch and could be a cause of stumbling and drive ability problems.

That's it Your done! If you have disconnected your TPS while the key was on you may have set another code so disconnect the negative battery post for a minute. Reconnect and start the car and go for a 20 minute drive for the ECM to catch up on it's relearn curve.