New 94 Ls400 Owner

[aaronls400]

I recently purchased a 94 ls400 and got a synthetic blend oil change and since then I feel as I lost some power, I don't know if this is the reason and don't know what oil the last owner was running. This has been an amazing vehicle but needs minor work, I would like some advice as to what I could do to boost power, the car had 180,000 miles on it but drives great other than the power loss. Also check engine light comes on for a few mins sometimes but always turns off before I can get the code read, any ideas on what this could be. Any advice would be wonderful, I would like to own this car for as long as possible.