Over the past couple of days I've pulled the Suburban out and been driving it a lot. It has been running fine. Now, when I go for a drive, the first 30 miles or so of driving is good, but once I get off the interstate or slow down a lot, the check engine light comes on. The engine doesn't seem to be running rough or complaining, so I just let it be. I checked the code, and it's OBDI code 42 which my Haynes book says is the Electronic Spark Timing issue. Trick is, the manual keeps referring to the HEI ignition setup, which I don't have. I have the normal electronic ignition system. So, I'm not quite sure where to start. A code 43 references an Electronic Spark Control module, which I think I do have, but it's not throwing this code. Any idea where to start looking? I'm thinking about checking out the ignition module under the rotor in the distributor, but until this weekend I'm not in a position to check it out. Any ideas?