Do you need to adjust the base idle on a GM TBI?

For whatever reason you have determined that you need to adjust your base idle on your GM TBI vehicle. In most cases this is only done if you have modified the internals of your engine or you have swapped a larger throttle body onto your vehicle.

What is the TBI code on a 1990 Chevy truck?

Consult a service manual or see below for any check engine light code definitions. You can use a late 80’s or early 90’s GM TBI definition. If you have access to a scan tool use a hook up for a 1990 350 cu. in. 5.7L Chevrolet truck. For some scan tools enter VIN 10th“L” 3rd“C” 8th“K”.

Why is my TBI fuel injection light on?

Troubleshooting your TBI Fuel Injection System Most of the problems encountered while installing your fuel injection system or after a time of operation are very simple. If your check engine light is on you more than likely have a hard fault meaning something is grounded out, unplugged, operating out of range or has gone bad.

Where is the idle speed setting on a Chevy?

Locate the vehicle specifications sticker, which is on the underside of the hood, and lists the factory idle speed setting. Tighten down the adjusting screw on the throttle cable linkage with the flathead screwdriver to raise the idle speed, and loosen the screw to lower the idle speed.

Where is the idle button on a GM TBI?

The “A” and “B” terminals are located on the top right of the connector. Unplug the IAC valve located on the passenger side, rear of the throttle body. Start the engine. Insert a T-30 size Torx driver into the Idle adjustment screw that is located behind the plug removed earlier.

What makes a’91 TBI 350 surging at idle?

It basically almost dies out, and then surges back to life (probably a little higher than normal idle), then repeats continuously until you apply some throttle. If I had to guess, I’d say it’s a dirty throttle body, or possibly injecters. If it is one of these, what would be the best way to clean them?

How do you change the idle speed on a T-30?

Insert a T-30 size Torx driver into the Idle adjustment screw that is located behind the plug removed earlier. Turn the screw to adjust the idle speed to 650 RPM +/- 50 RPM. Turn off the engine and disconnect the negative battery terminal from the battery using a wrench. Reconnect the IAC valve.

What makes a 91 Chevy surging at idle?

My father in law’s ’91 Chevy was running poorly, so we put new plugs, wires, cap and rotor on it, and it’s running better, but it it still surging at idle. It basically almost dies out, and then surges back to life (probably a little higher than normal idle), then repeats continuously until you apply some throttle.

Can you change the throttle body on a 350 TBI?

Modify the throttle body. This one pretty cheap but does require removing the throttle body. UTIMATE MODS . Stock 42mm TBI units flow around 450cfm which if you look at http://www.carburetion.com/calc.asp a stock 350 even with a cam upgrade to increase the powerband to 5500 rpms isn’t going to use much if any more than that stock throttle body.

What should the voltage be on a GM TBI?

Loosen the two torx screws holding the TPS in place, but don’t remove them. Rotate the TPS until the voltmeter reads between 0.45 and 0.55 volts, with 0.50 being ideal. Tighten the mounting screws (carefully, they thread into soft aluminum) and re-check the voltage to make sure it’s still within range.

How to reset the idle speed in a GM TBI?

Unplug the IAC valve located on the passenger side, rear of the throttle body. Start the engine. Insert a T-30 size Torx driver into the Idle adjustment screw that is located behind the plug removed earlier. Turn the screw to adjust the idle speed to 650 RPM +/- 50 RPM.

How to check the idle speed of a truck?

There are many ways in which you can do this. This bulletin defines the controlled idle speed and minimum idle air rate specifications for 1987 and 1988 model year trucks for all engine applications with TBI. Additionally, step by step procedures are provided for performing the controlled idle speed check and the minimum idle air rate check.

How do you adjust idle speed on IAC?

Turn on the ignition, but don’t start the engine. Wait 30 seconds. Now, go remove the connector from the IAC. Start 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”.

Do you need to adjust the base idle on a GM TBI?