DIY Dialog

Air filter thermac temperature sensor function.

  • My air intake Thermo Sensor was not connected on one side. I discovered this after replacing the TBI with a rebuild. I used a standard vacuume diagram to trace connections. Where can I find information for testing and replacing, if needed? I also need diagrams that include vacuume connections for heater controls which connect off the same line with a back flow valve, and then off to a round ball where the vac line ends. Any help would be appreciated. Greg

  • More information:

       When I tried to start my truck cold today it would not start. I disconnected vac hose to Thermo sensor and plugged vac connection to T at TBI. I disconnected and reconnected - battery term to reset computer. It now starts and at least runs reasonably well. Help!


  • We will contact you.

  • I ordered a new Thermo sensor. I also plugged the inlet at the air cleaner vacuume connection to the sensor. The truck now starts cold quite well. I will install the new part and make all the vacuume reconnections as my diagram shows. (And across my Fingers?) My main concern is not having a diagram that depicts my trucks vacuume configuration. Perhaps my VIN# and the correct web site could lead me to what I need?

  • Thank you for your subscription!

    Glad we could connect via email and assist with the vacuum diagrams and other information.

  • I installed the new sensor. I disconnected the battery to clear codes, which allows the IAC to reposition itself? The truck barely ran at first at low idle. It now idles different every time I start it, but runs better than ever at highway speeds. With all the right connections and new part will it just take time to learn to idle well again? I am out of my level of knowledge for what to do.

        Appreciate any suggestions, Greg.

  • Yes, it should get better over time.

    You can try the relearn procedure we just emailed.

  • After every attempt to get the idle issue to subside I still have trouble. The current consensus is that replacing the distributor is the obvious best solution. I trust the part from rock auto is a meticulously rebuilt TBI from Auto Line products.

         Facts are the engine has 225,00 miles, but has had excellent maintenance. The cylinders have acceptable compression within limits of each other, new plugs, rotor, cap.

       Symptoms: when starting cold I need to slightly depress gas pedal before starting to get motor to idle speed. After warm it will start at sustainable idle, but will exhibit poor uneven acceleration and irregular shift points.It can be difficult later to re-start and require depressing the gas pedal enough to re-idle until it settles down. Oddly, It really great at certain periods with power and smooth acceleration, but the bad cycle soon reoccurs.

        My understanding is the distributor controls shifting points and has a magnet generating electronic component for power control, and can affect the idle as well. There are no diagnostic codes, but the check engine light will come on when the engine starts idling really bad.

       My plan is to have the shop replace the distributor with new one; check torque on TBI bolts, and double check that all vacuum connections are correct.  I just ask your opinion before I proceed, and will share any results afterwards. Appreciate your feedback! Greg

  • That very well could be the distributor. We want to save you the time and expense of replacing a part that is functioning normally. Before you commit to replacing the distributor, there are basic things to check, such as the fuel pressure and base timing, among others.

    Your ChiltonDIY subscription has a lot of good diagnostics that will help you pinpoint the issue. PATH: Engine Performance & Emission Controls > Diagnosis & Testing > Diagnostic Charts

    Use a good scan tool. Even if a failing component (such as a MAP sensor) doesn’t set a code, it can still be faltering and the scan tool will show you.

    Especially check the TSBs (technical service bulletins), such as those about the fuel pump hoses.

  • My S10 is finally running better. A ground connection to the ECM had high resistance. The distributor was replaced with a new one. The engine feels more like the new TBI is learning to talk to the ECM now, and has mostly returned to normal.

       My question: The catalytic converter was replaced about eight months ago and has minor exhaust leaks front and back connections. Besides the monoxide, would lost exhaust back pressure affect engine performance, or O2 sensor readings?

        Thanks, Greg.

  • Usually small exhaust leaks will not cause performance issues. The only way your exhaust leak would play havoc with the O2 (oxygen) sensor, would be if the leak were close to the O2 sensor. In that case, the leak drawing air into the exhaust system could causing the O2 sensor to go lean, signaling the ECM (engine control module) to adjust. I would seal up the exhaust system, sometimes just the sound makes you think it's not running correctly!