94 Accord LX, 4 cylinder. OK, I was finally able to retrieve the trouble code by waiting a bit longer for the computer to respond. I was being impatient, my bad. A good lesson to learn.

It flashed a 12: EGR system. I looked at the vacuum lines and connections, and everything looks good. The car runs fine with no loss of smoothness or power. Good fuel economy.

Where do I start? These components are a bit pricey, and I obviously don't want to throw parts at it unnecessarily.

Thanks, Dave

The Lift Sensor is a common problem......however the MAP sensor is the true "Snitch" of the operation.
So you want to have the engine warmed up and bring the RPM up thru 1700 while checking for vacum on the #16 hose at the EGR valve.

Next is to test for plugged EGR ports; with the engine at idle apply vacum to the valve, or stick your finger under the cap of the EGR valve and raise the valve pintle. The Engine should stumble severly or die.

Disconnect the 3 pin connector from the EGR lift sensor, with the key on there should be 5V between yellow/blue + and green/blue - wires.

Beyond these checks I'd have to paste together the diagnostic tree for measuring voltage at the ECM pins; holler back if you need more help.

Thanks HD, that's plenty to go on for now.