1989 Pontiac Trans Am GTA Fuel Injection Tuning - 101 Tech Idle Mischief

Next on our to-do list was installing our Moroso plug wires. Our old wires had a few straight-boot plug ends that were sitting on our new headers, so their days were already numbered. The blue Moroso wires came completely assembled and numbered on both ends (except the coil wire, which requires one end to be put on by the user). It's amazing how quickly the installation goes on these wires: no trial and error, just grab the wire numbered for that plug, and put it on.

The plug wires look huge, but these 8mm wires, wrapped in a protective silicone-impregnated fiberglass sleeve, are perfect for their proximity to headers. This sleeve is also shrink-wrapped tight against the plug boots on both ends, creating a virtually sealed, protective envelope around the wires. To assemble the coil wire, we cut the unmade end to length, stripped off the insulation, folded the core over and pushed the boot on with WD-40 before crimping the terminal on...

...and then slipped on the shrink fit sleeve. We used a lighter to shrink the sleeve. Tip: The double-numbered ends allow for super-quick service of anything requiring removal of the plug wires.

After swapping the bracket onto the Moroso coil, it went on exactly the way the stock one came off. All connectors fit perfectly, and the dimensions were identical. Performance is not identical, however, as we noticed the engine started immediately on turning the key, and it seemed more willing to rev, most likely due in part to the condition of our loose stock coil.

Idle-Air Control Valve: Computer-Controlled Idle - The IAC valve (yellow arrow) is a way for the computer to meter additional idle air without getting involved in the cable-operated throttle blades. It mounts into the bottom of the throttle body on the passenger side. We took off the connector to allow removal of the valve.

Using a cheap 1 1/4-inch socket, we removed the IAC valve. The IAC body is very close to the bottom of the throttle body, requiring us to grind down the diameter of the outside of the socket to allow it to grasp the IAC body without spinning.

Minimum-Idle Adjustment: Low-Idle Speed - With the car completely warmed up and in closed-loop mode, we turned the ignition off and used a paperclip to make a "U" shape to short the A and B terminals on the ALDL (the socket is located under the dash by the drivers' right knee). The far right terminal is A, the ground, and the B is the diagnostic. We then turned the ignition on but didn't start the engine. After waiting 30 seconds, we disconnected the IAC valve connector.

We started the T/A and used a low-scale tach to get the engine idle to approximately 500 rpm. This will now be our low idle, or minimum-air adjustment, performed at the throttle stop on the driver side of the throttle body with a T-25 Torx. Tip: If your idle is too high, you might have an intake leak. Intake leaks are common in Tuned-Port cars because of the multi-piece intake plenum and runner design. Plug your IAC back in, and use carburetor cleaner to spray around all the intake manifold seams. If the idle drops consistently when the carburetor cleaner is sprayed in a specific area, you have located your leak.