Hi everyone, I am the proud & frustrated owner of a firebird that was my first car(I’ve had her 11 years now). I’m looking to get the car running close to factory specs again so it can pass emissions here in Massachusetts. And also so it can save me a few bucks in gas mileage lol . I’m hoping that some of you know the problems I am having and are able to help me.

91 Pontiac Firebird
305 TBI stock (103,500 miles)
5 Speed T-5
Stock rear end
Cat back exhaust 3” HF cat new o2 sensor


I have several things which concern me. One is a reoccurring SES light I searched on the forums and found the suspected sensor responsible (IAT). But when I removed my air cleaner assembly I found it was not plugged in. I have searched everywhere in the engine bay but can’t find the female end to plug it into. Is there something I’m missing? Am I going to have to splice somewhere and connect that part of the sensor?

Second thing that has me worried is I also have another sensor in my air cleaner assembly that does not seem to be hooked up at all. Its located towards the front of the car and is rectangular in shape. Do you guys know what it is, and what it goes connected to?


And I have a vacuum line that’s not plugged in, it’s on the Tbi unit itself facing the front of the vehicle in the middle. Don’t have a clue where it goes plugged in.

And last but not least my car over revs a lot mostly when cold , but also when hot as well. It happens when I depress the clutch in first and second gear the revs will jump to 2000-3000 range it feels like the throttle cable it stuck but I checked and it free so this leads me to believe that it’s a sensor, could this also be attributed to the vacuum line I’m missing?


Thanks you guys in advance for the help I understand my post was big but I wanted to make sure I got it all in one swoop instead of posting a thousand posts of doom.

P.s if you have pics it would help greatly lol .

 

Welcome aboard! You have come to the right place for help with your car.

I will try to cover your questions in the order that you asked them.

There should be an IAT harness plug somewhere in your engine bay. It should be more towards the passenger side near the firewall. The extension off of the engine harness for the IAT is roughly 6" long so it may have fallen down into the engine and could be hiding from you. Trace the main engine harness and see if you can find it. Plugging it in will solve your SES light.


You have a vacuum leak. When you installed your open air element you unplugged the vacuum source the the stock thermac system (little rectangle thing in your air cleaner). You left that vacuum port unplugged so you have a vacuum leak. You high "revs"/idle is a direct cause of this leak. If you go to any auto parts store you can buy vacuum line plugs that cost next to nothing. Find the one in the pack that fits tightly over that vacuum port and your car should run like normal.


If the car has never had a tune up now would be a good time. Replace the spark plugs (gapped to .035") as well as the fuel filter, and 02 sensor. A few minutes with a volt meter can also check the condition of your CTS (coolant temp sensor) and plug wires. You should also check your base timing and verify that it is in the 0° to 4° advance range (unplug EST and check timing with car at idle, adjust accordingly).

For more info on anything that I vaguely covered use the search function. Items such as adjusting timing and overall tune up tips are all over this website and can be easily accessed though the search function. Good luck and happy modding!

For more detailed pics on various TBI items refer to the new to TBI sticky linked at the top of this page.

 

Shiffty , im gonna take another look closer to that firewall and see if i can find something. what do you think about the injectors? what the easiest way to clean them? TIA

~Dirty~

 

You can always run injector cleaner through your tank but you may want to rebuild them if you suspect that they are not functioning normal (excessive drips at idle and or spitting/surging). If you are not ready to take on this task you can simply remove them and make sure that the screens and orings are intact and not damaged/worn. TBI injectors are very robust and will last and run normal for hundreds of thousands of miles.