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1989 Pontiac Trans Am GTA Fuel Injection Tuning - 101 Tech Idle MischiefTuned-Port Injection Tuning Basics For Smooth Performance From the February, 2007 issue of High Performance Pontiac By "Dr." Troy Avent Photography by "Dr." Troy Avent
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 Coil And Wires - We needed...  Coil And Wires - We needed to remove the coil bracket from our stock coil to mount our new Moroso ProCoil. The arrow points to the nub that was left when the stock coil's mounting rivets saw about 20 seconds on the grinding wheel. The new bolts are included with the Moroso coil.  While grinding on the rivets,...  While grinding on the rivets, the stock coil vibrated badly in our hands, leading us to realize that its body was actually loose on the thick metal magnet that surrounds it. We found out how important this discovery was once the new coil was in place. As we journey down the sometimes rock-strewn road of Third-Gen Trans Am care and feeding, it's helpful to make sure the basics are covered. Otherwise, installing all the fancy parts in the world will be met with limited success. Mentioned in a previous story ("Third Bird Heard," Jan. '07), the Third-Gen TPI Trans Ams are fun to drive and downright cheap to buy, relatively speaking, but more than anything else, they are a great platform on which to learn. To those who aren't familiar with port fuel injection, it can be somewhat intimidating at first, while to others more acclimated to later systems, they appear a bit archaic. But the biggest problem with the breed is that because of their current values, most have suffered from too little TLC, and in some cases, a complete absence of simple maintenance. Apart from the normal wear and tear of a 15- to 25-year-old car, TPI Third-Gens have proven to be generally reliable, but don't mistake that for a free pass in regard to tuning them. In this article, we provide a few simple techniques to ensure that your TPI car is running as smoothly and efficiently as it should. Since we only recently replaced the spark plugs, distributor cap/rotor, and air filter, we won't cover those in this story, but there are other wear items and adjustments to be made that should also be a priority on your to-do list. Please note that these adjustments should be done in the order in which they are presented, as the value of each is dependent on the one that precedes it. Conclusion
Now that our TPI system is properly adjusted, we buttoned it up and went for a drive to let the computer "learn" the new settings. We were very pleased with the results, as the T/A started much quicker, the "hunt" in the idle had disappeared, and throttle response was more crisp. Even the transmission seemed to shift exactly where and when we thought it should, regardless of throttle position. Sometimes it's the small things that make the big differences, giving our Third-Gen a refined and well-tuned feel and dramatically adding to the enjoyment of driving the car. Parts List
Moroso Blue Max ignition wires
PN 72402, approx. $115Moroso ProCoil
PN 72358, approx. $50 Next on our to-do list was...  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,...  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...  ...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...  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-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,...  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...  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...  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.  The cone portion on the end...  The cone portion on the end of the IAC Stepper motor must get a decent seal inside its port to meter the idle air properly. We removed any soot and made sure the cone seal area was clean and in good condition, using a bit of fine steel wool on the IAC cone. We also sprayed carburetor cleaner into the port and cleaned that out with the tip of a large Phillips head screwdriver wrapped in a rag, getting a fair amount of soot from that area as well.  Throttle Position Sensor Adjustment...  Throttle Position Sensor Adjustment - With the jumper removed on the ALDL terminal and the IAC plugged back in, we used a T-25 Torx to loosen the screws on the TPS, one very loose, the other slightly snug, so the TPS will stay in place when we get the right value. The protector on the front of the TPS connector unclips and swings out of the way, allowing the use of voltmeter probes (negative into the top terminal; positive into the second; the third is not used).  We brought our IAC valve into...  We brought our IAC valve into spec by gently pushing on it until it was slightly less than 111/48 inch from the base of the threads to the tip of the cone. Tip: Installing the IAC valve when it is extended beyond that measurement can cause damage; when installed too short, it will be outside the computer's adjustment range.  We turned the ignition key...  We turned the ignition key to "on," but didn't start the engine. Then we looked for approximately 0.540VDC or 0.465VDC to 0.615VDC for our MAF-equipped car (0.710VDC or 0.660VDC to 0.760VDC for Speed Density-equipped cars). We had to jiggle the probes to get a good reading. After the adjustment, we tightened the sensor, then rechecked to make sure it didn't move out of range as it was being tightened. Tip: Try to get close to the middle values as that gives the crispest throttle response.  Throttle-Valve Cable Adjustment...  Throttle-Valve Cable Adjustment - Our final task is to make sure our transmission TV cable is adjusted properly. This cable adjusts transmission-line pressure to different throttle positions, so it functions as both a kick-down cable and also firms up transmission engagements with greater throttle opening. First, we firmly pushed in the gold button and pushed the TV cable slider back towards the bracket; then we released the button. The TV cable slider should remain almost flush with the outside TV cable bracket connector (red arrow).  From the driver seat, we pushed...  From the driver seat, we pushed the throttle all the way to the floor. We could feel/hear the adjuster automatically clicking into the correct position. Back under the hood, we opened the throttle linkage by hand as far as we could. Tip: If the TV cable "clicks" any more (direction of red arrows, photo) by moving the throttle linkage by hand, the car is not getting full throttle from the gas pedal. The cause is often as simple as a poorly placed floor mat.
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