I have a 1991 Subaru Legacy with about 230,000 miles on it. In the past couple weeks the idle became really rough. It idles between 300 and 500 rpms. Jumping between the two quickly causing the car to shake pretty bad. Also when I start the car after it is warm it cycles up and down between 1200 to 300 rpms three times then settles to the normal 300 to 500 range. I changed the fuel pump, spark plugs, and ignition wires. Now I've run a few resistance tests on the Idle Air Control solenoid, coil, and all four fuel injectors. All test came back good except for one fuel injector. The fuel injector resistance was about 30 ohms higher. Is one bad fuel injector enough to cause these problems or is there something else I could be overlooking. I ordered the fuel injector but would like some input on other things I could check out.

sometimes warm start issues are engine coolant temp sensor

sometimes warm start issues are engine coolant temp sensor

 

 

Also, check for vacuum leaks and air intake leaks.