I am working on a friend's 89 C1500 with 350 TBI, problem is hard start, then when it does start it surges then almost dies then surges almost dies and keeps repeating this.

First I noticed bad plug wires (three of them were burnt by laying on exhaust manifold, I replaced the wires and rerouted them with hold down clips so as to keep away from manifold, ended up replacing distributor cap, rotor and plugs as there were burn marks from spark jumping in cap. None of this helped. Next I replaced Idle control valve on throttle body. I then took for a test drive of about 5 miles and stopped to put gas in it, during that short period it cleared up and ran as it normally should, but upon restart it started running rough again and barely made it back to her (the owners) house.

I have noticed that the right (passenger side) injector will sometimes keep injecting fuel after the engine is shut off for a few seconds, when that is happening you hear a slight electrical buzzing.

I purchased an OBD I to OBD II adapter cable in order to try to retrieve codes but could not get either of my OBD II code readers to work on it, so I did the jumper wire procedure and service engine blinking and got the following code 12 three times, then code 22 three times then code 33 three times then 44 three times and finally code 45 three times. I have checked for vacuum leaks and have not found any, I did cap a fitting on the outside edge of MAP sensor which did not have anything going to it. I also removed the throttle position sensor with the intention of replacing it but the part I got was not the right one, It had slightly different electrical connection coming out of the side of the sensor and a round plastic connector with square hole to meet up to throttle linkage whereas the sensor on this vehicle had the electrical connector coming out of the top of the unit with a metal arm that hooked up to the throttle linkage.

While I had the unit out I took resistance readings from center connection to right connection and the resistance increased as I turned the actuator lever and then decreased as I released the lever, and the resistance was the opposite when checked from the center connection to the left connection. I checked the new part and it reacted the same way as the original one, I think this rules out a faulty TPS?

I disconnected the battery in order to clear codes and rechecked and found code 12 three times (normal) but have not been able to drive for a "run cycle" because I cannot get it to keep running, just the surging up and almost dyeing as I said in the beginning of this post.

I have purchased a new MAP sensor but do not expect it to have any affect.

As I previously stated, after I replaced the Idle air control it cleared up and ran perfectly ( for maybe 10 minutes until I shut it off to get gas, upon restart it slowly went to hell again.

The vehicle has no rust and body is in good shape, we want to save it.

Any advise would be greatly appreciated.