I thought I would ask the collective knowledge base. I've got a 1960 182C. At idle on the ground, the manifold pressure is up around 16-18 inches. I verified the plumbing is tight from the manifold to the gauge. I then checked the intake system for leaks by blowing clean air (shopvac) into the air box and then using a spray bottle with soap solution. I found a few leaks in the coupling hoses which I fixed. The engine seems to run smoother in cruise but it still reads about 16 inches at idle. The only other leak I found is around the throttle shaft bushings on the outside of the carburetor and it's fairly small. My question is where is the system sucking air with the throttle at idle to give such a high manifold pressure? Could the carburetor be that worn out or is it something else I've overlooked? The airplane is fairly new to me but I am assuming the manifold pressure should be down around 10 inches at idle on the ground. Any help appreciated.

Do you know the gauge is working, does the gauge show correct values at other settings?

At 15", I would have thought the engine would be running noticeable leaner than normal, have you confirmed this with a lean-test checking for RPM rise?

Thanks, yes I checked the plumbing and gauge operation with a hand operated vacuum pump. Works great through all ranges. You raise a good point about the lean test, I get a nice rpm rise at mixture cut-off. The only thing I can think of is the carbeurator or maybe valve overlap? Is that even a possibility?

Did you check the primer system? Even a small leak has a big impact on things. When mine broke in flight, I thought the engine was not long for the world even at full rich....the cylinder seemed completely unhappy.

Just a thought,but fairly easy to test anyway without uncowling the bottom end. My problem was the tubing fretting on the fins. Since then, I've had loose compression nuts too.

Check the MP line between the intake manifold and gauge for pinhole leak. Also, check crossover tube in the front for wear due to cowling chafing.
RP