jgood

I purchased a 96 ES300 last week with 125k miles. I drove it about 500 miles so far, and it had no issues, other than a severely leaking rear valve cover gasket. I replaced that today, along with the plenum gasket, throttle body gasket, and EGR valve/tube gaskets.

Got it put back together, and the car has a very rough idle now. It revs fine, accelerates fine, has great throttle response, doesn't smoke. It throws a CEL after 5 minutes or so of running. P0300 through P0306, all misfire codes for each cylinder.

I sprayed starter fluid, it smooths out and revs almost anywhere I spray it. Plenum gasket, valve cover gasket, vacuum hose connections, fuel injectors, literally anywhere. That alone baffles me. I tightened everything properly, cleaned mating surfaces, etc.

Next up is a smoke test, but I figured I'd post here to see if anyone has any other suggestions. I'm not familiar with these cars so I don't know of any common issues. I did triple check the vacuum hose routing, I took before pics and also checked against the diagram on the hood. The hoses were also slightly formed from age, and most fell right into place anyway.

Thanks in advance for any input/suggestions.

jgood

Smoke test made the issue immediately apparent.

The throttle body gasket was installed wrong, rotated 90*. Doh!

mitmaks

Glad you figured it out.