[car guy]

I have a 1986 Pontiac Grand Prix. The car has 100K miles but is still in like new condition as I bought it new and have maintained it. The car is all stock with the 305 4bbl engine. I read somewhere that if your car has over 75K you should change the oxygen sensor. So I did and the car seems to run better but now it is throwing a code 53 with the check engine light on. I thought maybe the computer was just readjusting to the change so I cleared the code after driving 20 miles. The service engine light come back on today and had reappeared a couple times after restarting the engine. I purchased the sensor from Auto Zone and it is an OEM style Bosch. That code refers to the EGR but why would that come on after changing the O2 sensor and what is the recommended or most common fix for a code 53? Thanks

[judgethis]

Check your vacuum to your EGR valve soleniod at idle. Should be over 7". If not check for vacuum problem. Also with the engine running push up on the uderside of the EGR-engine RPM should drop. If RPM doesnt drop then EGR port is plugged. Check your vacuum after the soleniod at idle and should be zero. You ma have a problem with the EGR soleniod.

[Oreif]

It is the EGR/Purge/TCC/TVS module that trips the trouble code. That is where the ECM sense line is hooked up at.

If you follow the vacuum line from the EGR it goes to a "T". One side of the "T" goes to the EGR bleed solenoid and the other goes to the EGR/PURGE/TCC/TVS module.
Check the all the lines as well as the electrical connections. Did you possibly bump or crack a vacuum line when changing the O2?
You could check in the area that you were working in to see if you accidently bumped a vacuum line or electrical connector.


Here is a vacuum layout for the 305:

[car guy]

Thanks both of you for the help. I just got the time to check it out and the small vacuum line from the EGR was dry rotted so I replace it and cleared the codes. I drove about 30 min. and so far no code has shown up.

Now I am the original owner and other than some warranty work no one had touched the engine but me. The T you speak of has one hose to the EGR and another to the module( my guess that is what it is it has electrical plug also an is at the back of the engine), the other part of the T is capped off with a plug. I will have to go follow your diagram tomorrow and see what is missing an replace it. I wonder how the bleed of being unconnected affects the car and how much better it will run hooked up? This car has always had a hard start problem when the weather is above 75 degrees.