2007 camry with rough idle when ac is on. Runs fine down the road,still gets great fuel mileage,what is wrong?

Fuel pump

Does it run rough at hot idle ? How many miles ? Any recent work done on engine ?

Vacuum leaks work like this. A small hose breaks, you don't notice a engine problem, but the gas mileage goes down a bit. As the leak progresses, mileage goes down more. A large leak you notice the engine runs rough at idle. Combine this with clogged air, fuel filters and clogged catalytic converters and it will start killing the engine at stops and eventually go down the road. But to answer your question, No the line going to the diff, wont affect the engine performance. Because the PCM will compensate for the small leak. More fuel.

Throttle plate may need cleaned and check your plugs.

Check the fuel pump , filter, throttle position sensor.

I believe your A/C idle up valve may have failed. They do this when hot, but test OK when cold. See here p228

http://www.turboninjas.com/camry/eg1.pdf

ive had a problem like this before it turned out being a shim under the camshaft worn and when idle it wasn't pushing the valve down properly.all it took was shimming it out.might want to check that out pending your mileage.

make sure you put the right plugs in the fault is most likely the coil pack follow the plug leads from the spark plugs and you will reach the coil pack about £60

You need to Replace your Gas Cap. The Seal is worn and it is allowing Air to get inside the Fuel tank Causing your Rough Idle.

I had the same problem with my 99 Cherokee. I was told to replace the blower motor for the carburetor, works great and gas mileage improved.