Mailbag: Solving Fuel Starvation and Idling Problems in a Tuned Port Injection Pontiac

You’ve got questions, we’ve got answers. We work with the Summit Racing tech department to help you tackle your auto-related conundrums. In this week’s Mailbag, we’re troubleshooting a Pontiac Trans Am Tuned Port Injection engine that’s experiencing both idle and off-idle stumbling.

tuned port injection pontiac engine


Q: I have a 1988 Pontiac Trans Am GTA with the 350 engine. I installed an SLP three-inch cat-back exhaust system, 180-degree thermostat, and a K&N air filter. The car has 50,000 miles on it and has never been in the rain or snow.

Recently, I have noticed that when I start the engine cold, it stumbles and dies out. On the second try, it starts and runs fine. I have also noticed the acceleration is not what it used to be, especially with the air conditioning on. The car will also stumble and try to die from a standing start with the transmission in Drive. It seems like the engine isn’t getting enough gas at idle.

I did the last tune-up on the car about four years ago. Could the problem be dirty fuel injectors, a bad fuel pump, idle speed control, or something not fuel system-related?

A: The Tuned Port Injection engines in these cars have a reputation for developing both vacuum leaks and dirty throttle bodies. Either of these can cause the idle and off-idle stumble problems you’re having. We recommend looking at both to find a solution to your problem.

Also, be sure to check your fuel pressure. It should be 36 psi at idle.

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  1. David W Henninger says:

    80s TPI engines are notorious for sticky poor flowing injectors. cleaning sometimes helps but usually replacement does the trick

  2. Or you could replace the fuel filter and see if that helps.

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  4. 5.7 tuneport
    Starts up cold good goes norm idle
    Start to ilde from 600 to 1200rpm surges up down any ideas fuel psi is 37psi shows no codes

  5. I have a 1990 Chevy 454 tpi it have new tune up for most run ok the problem is when you first start up in runs rough idiot it acts like the computer takes time to catch up with it to make it run even write no codes on your computer no lights on the dash only one code flash is 112 so after it is running for a bit runs fine then turn off the motor to go into store come out starts right up then dies or starts right up And run route runs rough for a few then it runs just fine when you give it gas passes in gear it falls on his face but then takes off wind gauge tuneup had to replace screw in distributor so had to pull distributor out to fix wind pulled out rusty icky looking hard to getNew rotor on had to clean real well finally got it on and it was running fine new wires plugs Rotor seem to make it run a lot better but then right back to the same problem get to the store after right driving it and won’t start it’s three times to get it to stay running it will start every time but then die at wits end

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