GMC Repair: Electronic Spark Control?, gmc sierra, throttle positioning sensor


Question
I have a 1993 GMC Sierra.5.7L(350).This is also the only vehicle we have and do not have anything else to drive.
All of a sudden the truck started acting like it jumped time.But, I found that it would crank and run after it cooled off until the motor warmed up.Which I removed the Ignition Module and had it tested.It was defective.I replaced it and reset the computer.Cranked the truck.It did crank but,it still runs very rough and dying on idle.So,I ran the ECM through a test and was given code 22 (Throttle Positioning Sensor Defective).I installed a new TPS,reset the computer and I got the same result(motor running badly with popping,backfiring,and engine dying while idling).I scanned ECM again and now I am getting code 43(Electronic Spark Control Circuit  {signal to ECM has remained low too long or the system has failed a functional test}).
I have been through every diagram that I can find and cannot find one that shows where the ESC is located.How do I find it or does this sound like there is a totally different problem other than the ESC or is there even an ESC on this model.
PLEASE HELP!       THANK YOU!

Answer
Hi Eddie. There are 2 timing systems on your vehicle, one is electronic timing,EST, which controls the actual timing of the ignition system according to present conditons such as throttle postion, map signal, speed signal etc. The electronic spark control ESC, is designed to RETARD the timing when the engine senses a spark nock or pinging. If you use a cheap grade of fuel and you are getting pinging, the ignition control will RETARD the timing to stop the pinging, this will also reduce your power. Any noise in the engine such as a lifter knock will make the ecm beleive there is a spark knock and RETARD timing. There is a knock sensor on your engine, it should be located just a few inches in front of the starter and has a single wire on it. The sensor is round, about 2 inches in diameter, you can disconect it and try driving the vehicle to see if it makes any difference although this will certainly not explain the dying at idle, also, be carefull changing the knock sensor, it screws into a cooling jacket and you will burn and scauld yourself if you do not drain the cooling system before removing it. The 5.7 engine has problems with the ignition coil and coil wire, also, there are problems with the egr valve and egr control solenoid holding the egr valve open at idle, that would explain the stalling. remove the coil wire and check for corrosion, if there is corrosion, replace the cap, rotor, coil. also, check the spark plugs and the ignition wires for sign of arching, a good way to do this is the spray them down with a non flammable cleaner such as 409, fantastic or the like. The problem you have could be caused by almost any thing from fuel injectors to fuel delivery and ignition problems, i know i haven't given you a specific answer, but i will work with you on this until the problem is solved including sending you my phone number if it gets really involved. get back to me and let me know how you make out---MANNY