Thanks for the information. I ask because I have trouble with my car it starts but rpm dips down and back to about 850 rpm .I tested idel control everything check out good tps is on 98v .checked for vacuum leaks good. Maybe spark plugs I have are no good I have motorcraft sp502x and think they are bad.
Then like nickyb indicated the surging idle check list is your friend. Follow it step by step and do not skip around. The success rate of fixing the problem is really high if you do it that way.
Updated 05 July 2022 to add rough idle when cold and smooth idle when up to normal operating temperature. See the EGR tech information, section #15 for more help.
Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank Checklist. They are very effective in finding and eliminating the problems by use of a systematic process that checks and eliminates possible causes. This idle problem checklist will use the same troubleshooting strategy and methodology.