Im having problems with my 93 lexus ls400. I know i need to replace my starter. Its got problems at times while turning my key. One day when first starting the car for the first time somthing happend that made a very rough idle. Like it was a misfire. As i drove the car it felt like the front of the car was bouncing up and down while my foot hit the gas. I figured i needed a tune up. So i replaced plugs wires and distributer caps. I thought about the ignition coils. But did not have the money and i was not sure if that was part of the tune up and what they where for ( i have never had a car like this one) so after the tune up the car had strong power but it still had the same problem. As i was diving it home the car got slower and my car would not move. I had to floor the pedal just to make the car move. But it was hard and slow and i made the engine smoke. It went in reverse just fine but would only inch forward. So i took it in. Found out that my car was working on 4 of the 8 cylinders only. So they replaced the ignition coils. My car started to drive again. However the problem is still there but in a different way. The car drives but at a certain speed the jumping feeling starts up and it still feels like a missfire. Im sucking up gas very fast. I went from 14 miles to a gallon to 11.. And the engine still feels rough at idle and drive. now i took it into pepboys and they hooked it up to a machine and no codes came back and no check engine lights was on. They beleve its a cylinder head problem. I still feel like its a spark misfire problem. Another mechanic checked it out and still no codes or check engine light. I called up the dealership and besides telling me to bring it in and give the car a tune up ( i guess they did not understand when i told them i gave the car a tune up ) they had no idea the problem either. I feel i may have blown the new spark plugs due to force driving it home on 4 cylinders instead all 8 before replacing the coils. I do not have money to replace random parts in hope its whats wrong. I have a smell of fumes like my muffler coming from the engine. The fumes smell heavly gross of paint thinner. What is this problem With my car ????????????