What does spitting back through the intake suggest?

Spitting back through the intake suggests that the intake valves are not properly seated. When the intake valves fail to create a proper seal, it allows the combustion process to push some of the exhaust gases back into the intake manifold. This backward flow disrupts the air-fuel mixture and can lead to performance issues in the engine, such as rough running or difficulty in starting. Properly seated valves ensure that gases move in the correct direction during the combustion cycle, maintaining efficient engine operation.

In contrast, excessive fuel pressure could result in a rich mixture and other symptoms, but it typically would not cause backfiring through the intake in the same way. A clogged catalytic converter affects exhaust flow and may lead to different performance issues, such as increased back pressure, but does not directly cause spitting back through the intake. On the other hand, a damaged air filter primarily impacts airflow into the engine but does not lead to symptoms of spitting back through the intake.