1999 Toyota Solara SLE v6

I bought this car a few months ago and shortly after buying it noticed a roughness when driving around 40 mph with little to no load on the engine. It also kind of pulses when driving very slowly. There was never any check engine light so I went through the normal things-plugs, wires, mass air flow sensor, and nothing helped. I asked an expert on allexperts.com and he said that about any engine or transmission problem on this car should illuminate the check engine light, so I don’t know where to go from here. Any suggestions?

Re: the pulsing (surging) problem.

Check the following: Intake air (vacuum) leak
Possible worn fuel pump (Have fuel pressure checked)
Faulty IAC (Idle Air Control) valve (clean or replace)
Faulty emissions controls or a partially plugged fuel filter