I have Toyota Camry 1998, 130,000, V-6. When engine suddenly lost power, I checked the diagnostic code: it was P0302 (sparkplug #2) and P0402 (EGR). Also, the valve cover gasket started to leak oil (top head). Oil loss was moderate (I had to refil once per month) and I did not notice any smoke coming from tail pipe. I paid mechanic $300 just to replace all 6 sparkplugs and replace both oil cover gasket kits. Immediately upon leaving his garage I notice smoke coming out of my tail pipe, a lot. Three days later I measured oil level - I burned almost 2 quarts; new gasket is o'key so oil was most likely burned and went through tail pipe. Immediately I rechecked diagnostic codes: this time it was P0301, P0302, P0303, and P0402. I went back to the mechanic and requested answers. He told me that in addition to changing sparkplugs he removed residues of " sludge" under the valve covers. Also, he told me that after he cleaned " sludge" oil flows easier and that is why my engine suddenly started to burn so much oil through the piston's rings. It does not make any sense. In summary, before repair: gasket leaked oil, sparkplug #2 had random misfire and to the best of my observation tail pipe did not smoke and there were no unusual smell coming from tail pipe. Two hours later, after the repair, code shows that 3 sparkplugs misfire although the engine runs smoothly and has more power that before the repair, gasket does not leak, but engine smokes excessively burning two quarts oil in 3-4 days. And the smell of the smoke is really bad. I appreciate your expert answer. Could oil be entering combustion chambers through valve? I also suspect other failure or damage caused when the mechanic took off the entire manifold/intake/EGR assembly to get access to second oil cover (otherwise unaccessible)?