I am trying to address an ongoing misfire issue on cylinder #3 (P0303) on my 99 Corolla 148,000 miles. I have already replaced all spark plugs and wires, all 4 fuel injectors, new air filter. Car only misfires on one cylinder (#3) and only in the morning when I first start the car. Once the car reaches normal operating temperature its smooth and runs fine. In the morning on a cold start I can also smell gas from exhaust pipe.(might be running too rich?) If I drive the car before it reaches normal operating temperature the car idles rough and shivers like its going to stall but has never actually stalled. It takes a good 15 to 20 min of driving for the engine to smooth out. My mechanic thinks it can be a leak in the intake manifold gasket. My question is can a leak in the intake manifold gasket cause a misfire on only cylinder#3 (P0303)? Thank you in advance for your feedback and expertise.
