Rough idle, poor fuel econody


2006 Nissan Micra, K12, 80,000 miles.

Over the last couple of weeks it has developed a rough idle and the fuel economy has dropped from its mid 40's to around 35 - almost a 10mpg loss.

No MIL light, no misfires, no stored codes, no pending codes. Delphi shows no errors, but does show IAT at 27'c when the engine is warm, whereas the outside temp was 9. I've replaced the spark plugs (anyway), put 2 tanks of E5 through it with some redex, new air filter. Cleaned the throttle body and MAP sensor, no difference.

I don't think its a vacuum leak as I've tried propane around the hoses whilst the engine is running.

Any other ideas?