I have been slowing trying to tune my engine after a few small changes. Everything was running well until today. I made no changes to the engine between yesterday and today. Today I went to start my car and the it was not idling well. My air fuel readings were 13.0 on average until today- now they are 18. Then I turned the car off and the readings were 15. I turned the car off again and the readings were 17.

I hadn't made any changes. The car doesn't run well now. Doesn't improve with changes in the idle mixture screws.

My air fuel gauge was recently calibrated. New o2 sensor. My fuel pump is new and sounds to be working well.

I was thinking fuel filter or some other fuel pressure issue. I purchased a fuel pressure gauge however it is on order. I will purchase a new fuel filter tomorrow.


Any ideas?

Pressure, pump, and idle jets
Clean the idle jets, see if that helps.
It takes five minutes.

Cleaning out the idle jets and removing and cleaning the mixture screws (needle valves) and ports where they screw in would be my first idea. If that doesn't work I'd look for vacuum leaks. Being that lean isn't good. If it does turn out to be plugged jets I'd look at better air and fuel filters.

Idle circuit doesn't need a lot of pressure. I wouldn't look at pressure issues unless this problem happens on the main circuit after a hard pull.