Mustang, 1992 2.3L dual point OBD 1 error codes problem

Have you checked for spark on all 8 plugs? Unplug the exhaust side coil pack and run the engine. Does it run on all 4 cylinders?

I have a 2.3L 92 mustang and had intermittent codes 223 and 224 and the RPM meter would report 1/2 the normal RPM even though the car idled at the normal RPM , I took the ICM out and had it checked at AutoZone and it wouldn't fail on their tester even after running it a dozen times. I did the ford resistance diagnostics and all the external stuff looked good. I even had new coils and wires put in 2-3 months ago since I did have a misfire problem back then but no codes associated with that. In the end I ordered a new ICM module on eBay for ~$90 and installed it and the problems went away. I read on other sites that people had similar random problems and they replaced the module as well. Guess the module goes bad after 22 years of use. :) BTW the ICM manufacturer wants you to put the 4th screw in so the heat sinking works right ( the module back is slightly curved making full contact dicey) but blind drilling and tapping the hole was a real pain but I got it done by taking the alternator off and using a Dremel tool. . The original screws are metric but I tapped the 4th hole as 8-32 and used a few washers to get the screw depth right. They also didn't include the dielectric grease so you need to get some of that as well before installation. Some manufacturers might include it so you have to check.