Hi everyone,

After a cold start (like in the morning), after the engine warms up to a certain point, I get a check engine light (CEL) code 12. If I turn off the engine and restart (engine now warm), the CEL won't come back. So, as long as the engine is up to a certain operating temperature, I get no CEL. The CEL only comes on during the transition from cold to warm engine temperature. I've cleaned the EGR valve and checked the plunger operation with applied vacuum. I've not checked the EGR passages nor voltages. Please help me diagnose the problem. Thanks so much.

 

Check voltage on the valve when cold. It could be thermal failure of the sensor, wiring or connector.(corrosion, open circuit when cold, etc etc)
Clogged EGR manifold would not cause a code 12. 12 is only for the lift sensor on top of the EGR valve.

 

Thanks Mike. I found out it was a disconnected vacuum line from the EGR valve to the EGR control box. Now there's no CEL. However, now there's more vibration. Can EGR function affect engine vibration? What should I check next?

 

If the car is now vibrating/stumbling at part throttle it is most likely due to the EGR manifold and/or ports into the runners are partially blocked. What you are feeling is part throttle lean misfire.
EGR will not(should not) operate at idle. If it is recheck the vacuum line connections are correctly routed.

Easiest way to clean the EGR manifold is to use a #1 and #2 flat head screw drivers. They are perfect for scraping out the majority of the manifold portion of soot, and the ports to the runners can be cleaned with the #2 and #1 flat heads by gently drilling into the carbon. Ports are stepped, so the #2 will work to a point and then use the #1 to clear out the rest. Use a shop vac while drilling out the ports to keep the junk out of the intake. I don't use TB/Carb cleaner as it just goops/gunks up the carbon and makes a slushy mess.

 

The previous owner likely disconnected the vacuum hose so it would turn off egr, and when it did and it turned the egr code on and the egr system off, it would run fine. With the hose reconnected you will need to clean out the ports, which, assuming your car is the 95, is fairly easy compared to most cars. Eric the Car Guy has a good video on youtube for this.

 

Mike/Holmes: Thanks. The vibration is low but noticeable. You feel it at the steering wheel and in the seats. The idle speed is constant and steady (~600-700 rpm, 2nd mark up). I'll check and clean the EGR manifold this weekend.