After 2 treatments of AC Delco Cleen (1liter for each treatment on 2 successive days throught the braker booster hose) I was sure that a lot of carbon got burned out through the exhaust. The second treatment produced very little white smoke compared to the first treatment a day earlier. I'm now noticing that my engine seems to be idling less smoothly after both treatments. At high RPMs it seems fine.

Did any carbon get dislodged and stuck somewhere? I'm guessing either the EGR valve, EGR vacuum modulator or the O2 sensor got plugged/dirty...

Any suggestions?

Troy

 

Those would be good places to start.

 

The spark plugs are probably full of junk too. I'd say pull and clean/replace all the plugs then pull and clean the o2 sensor(s) with some throttle body cleaner.
Just an opinion.

 

Spark plugs are clean. In fact the ceramic part was almost white. I guess the cleaner did them also. I'll pull the front O2 sensor and check it. Can it be sprayed with electronic cleaner without harm?

Troy

 

Electrical cleaner won't do much to get rid of the carbon on the sensor. You can soak it in carb cleaner (look for sensor safe), but then hit it with electrical cleaner to ensure it is residue free before reinstalling it. Sometimes the sensor is on the way out and the top end cleaner is the straw breaking the camel's back (can even foul a new sensor too). Worth a shot anyway.