Code 42.... HELP!!!!

[adot]

Code 42 has got me going crazy! Let me fill you guys in on whats been going on with my "90 burb". While warming up the burb one day I heard the engine start to lope, so I check it out and the check engine light came on. So I get my little tool and code 42 is what I get. I check my book and it says I have an electric spark timing problem. So I check for shorted or grounded timing wire, but all looks good. I do checks on ignition module, and the pick up coil, every thing still checks out ok. So I clear the codes, and drive the burb for a couple days. Then once again while warming up, it does it again. I've noticed a loss in performance, and my gas mileage has gone down. Hope some one out there can help me out.