Trembling TPI - My '85 305 TPI Trans Am is driving me nuts. The car is in beautiful shape and runs well, but the idle quality is awful. It never idled great even when new, but now it feels like it has a dead misfire. All the ignition parts have been replaced and are good. Do you guys have any ideas? It has gotten to the point of embarrassment-I don't even want to drive the car. By the way, there are no codes in the computer and the Check Engine light never comes on. Paul Clarke of Council Bluffs, IA
Ray Bohacz Responds: TPI systems need to be diagnosed as if they were engines with eight individual carburetors, since there is an injector for each cylinder. The most common cause of an unstable idle that acts like a dead misfire is either fuel injectors that are not atomizing the gasoline properly or an air leak in the TPI manifold. Your car may have both conditions due to its age. An additional source of air leaks with these engines is the rubber O-ring that seals the injector to the intake manifold. The same O-ring is used to seal to the fuel rail, but if that failed, it would cause a gas leak.
Your Pontiac was equipped with cast-iron cylinder heads, and since the intake manifold is aluminum, there is a difference in the rate of expansion of the metals. Over time, this may cause a slight air leak that is isolated to one cylinder. Likewise, the extreme underhood heat generated by these cars takes its toll on the injectors and seals. It is common for the rubber seal to introduce a small amount of air into a cylinder and create a lean misfire, which would feel like a dead miss with an EFI system.
Given the age of your Firebird, I would remove the fuel injectors and send them out for service to Marren Motorsports, (203) 732-4565. Tim Marren is one of the best injector people in the country, and he has a precise method of both testing and cleaning fuel injectors. This service runs around $22 per injector and would include new O-rings.
While the runners are off the engine, take the opportunity to retorque all the intake manifold bolts. You might also want to change the EGR gasket while access is easy. Then reassemble the runners with new gaskets, and your TPI's idle should be restored. While the intake system is apart, do a good job of cleaning the throttle body, and install a GM gasket kit to eliminate the possibility of leaks in this area.
It's hard to believe, but your Pontiac is more than 20 years old, and many of the seals are starting to fail. What I described is standard maintenance on these engines and is usually overlooked by most owners. Good luck!
'05 GTO Exhaust For '04s? - I have an '04 GTO, and I love the car, but the lack of a dual exit exhaust really bothers me, especially when I saw an '05 with the new rear bumper. Can I just buy that bumper and the '05 exhaust and bolt them on? Please let me know-I'd love to do this. No name given, via Internet
Chris White Responds: Actually, the '05 rear fascia is a bolt-on, but you need to buy the '05 rear styrofoam energy absorber (or modify the '04 piece to fit). The '05 exhaust is not a bolt-on to an '04, however. If you are looking for increased performance and a better tone to boot, Stainlessworks (www.stainlessworks.net) carries an '04-'05 rear fascia conversion exhaust that will bolt up perfectly and give your '04 an aggressive tone. The kit is complete and utilizes mandrel-bent 3-inch stainless tubing and quality hardware. This is by far the easiest way to put the '05 fascia onto an '04.