Cadillac Repair: 1990 Cadillac Seville 4.5 V8, coolant temperature sensor, 1990 cadillac seville

Question
Car will not start unless you press gas pedal while cranking starter. Will start but will not idle until warms up. Runs OK warm but idles rough in drive. Idles much better in park. Where should I begin trouble shooting problem?

Answer
Hi Rick,

      Reading troublecodes for current...EE...or history...E...is a good place to start. With the key on or engine running push off and warmer for 5 seconds or until the climate control panel goes into diagnostics and see what codes are displayed.

      Making sure all the tune-up stuff like plugs, coil, cap, rotor and wires need to be in good shape. If they have over 50,000 miles since they were changed then that might be all you need to do is do a tune-up. Just make sure to install the AC Delco plugs and stay away from the Bosch and Autolite brands because they make a Caddy run worse.

      If the TPS/throttle position sensor happens to be flat across the face instead of a molded edge install a new one.

      The fact that you need to press the gas pedal to tell the computer to put more gas into the engine could mean a defective coolant temperature sensor. You would need to check the coolant temp and ambient air temp sensors cold like before the first start of the day and see what they read. They should be the same.

      The oxygen sensor might be more to the lean end of the scale. It should read around .450V when started. You might try unplugging the sensor connector and see if it improves the running. If so then replace it.

      Cars of that year are known for having bad fuel injectors. Use your ohmmeter and see what they read. I believe cold they are around 12 ohms but if any are more than 2 ohms difference than the average then they are definitely shorting and will cause a rough idle.  

      Check for correct fuel pressure and that the fuel pressure regulator doesn't have a hole in it allowing gas to go into the vacuum line and into the engine. The fuel pump could be weak or the filter might be restricted.

     Start with those things and see where that leads you. Let me know what happens if you need anymore help. Bill