'91 300E 3.0 check engine light, code 17, after 02 sensor replacement
 

Hello all,

After a fruitless search of the archives, I figured I'd post my question. First some background:

Blown headgasket, went in for repair, crack in head not noticed after head rebuild, coolant got into exhaust (quite a bit), head got welded/fixed, headgasket problem now completely sorted, but check engine light came on, indicating code 17, bad 02 sensor.

For the first 1-2 days after repairs, with exhaust relatively full of coolant, car had some trouble coming up to proper idle speed after coldstarting--it would barely fire, chug along at 400 rpm, then idle nearly normally after 30-45 seconds, although it would still hesitate on larger applications of throttle until more warmed up. These symptoms went away after 100 miles or so, and car ran increasingly better.

Then, shop replaced 02 sensor, check engine light still came on, code 17. Shop did M-B fix of adding another ground to old 02 sensor, checked + adjusted fuel mixture with C02 meter, everything seems fine, car runs fine, but check engine light still comes on, still gives code 17. check engine light wasn't on before headgasket repairs. Car now starts fine cold.

We know the troubleshooting routines, but I ask to see if there are any obvious things we're overlooking.

Thanks!

Kristian Soholm

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