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Are you sure it's the red Check Engine lamp (problem detected) and not the yellow Service lamp (oil change due)? If it is the Check Engine lamp then most, but not all faults are considered serious enough to cause the lamp to illuminate and remain lit, as indicated for each DTC (diagnostic test code) in some reference sources. When a condition is no longer present (such as at a restart) the lamp may reset for some non-serious faults, but the code should still remain stored in the OBD (on board diagnostic) system. Up to 3 different codes can be stored by each OBD control module, any subsequent codes are ignored.
At the OBD diagnostic connector under the hood you should now check to see if there are any codes stored other than the normal 1-1-1. The procedure is described here in the 700/900 FAQ
https://www.brickboard.com/FAQ/700-900/EngineOBDCodes.htm
Your '89 240 has first generation OBD (OBD-I). You need to check for codes in both port 2 (LH 2.4 fuel system ECU) and port 6 (EZ ignition system controller). Keep checking codes until you get 1-1-1 or the first codes repeat. Be sure to do a reset on each port when you're done if you get anything other than 1-1-1, or you can simply disconnect the battery for a few moments. Your '89 doesn't have things like ABS or power seats so there are no other ports to check.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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