Too many codes

[nerflhopper]

My sons 1st car is a 92 sho w/250k. It ran well enough at test drive that i gave the boy a "thumbs up" for his 1st purchase. A few days after we got it home, started running rough, so, thinking the way I do, threw plugs and wires on it. That helped for a bit, then all the codes started popping up. 114 ACT, 556 Fuel Pump Relay, 334 EGR Valve Position Sensor, 214 Cylinder ID sensor, and 121 TPS.
Problem is, car will start well, run smooth, then after driving a short distance begin to run very rough. We plan on starting to address these one by one, which do we start with? Are there any that will inherently cause major misfires over others? This is my 1st dealing with these cars so I admit being very much a novice when it comes to working on them.
Any help in the right direction would be welcomed.

Aaron's SHO, Dan's wrenches

 

[jmpSHO2nd]

Was there oil in the plug wells when you changed the plugs giay nam? I would start with upper and front 60k clear codes and see what pops up for codes after.

 

[zoomlater]

Welcome to the forum. A front and upper 60K are good things to do to get the car in top running shape. But you can try and trouble shoot each code first to see if you can find if its just one or two sensors that have gone bad.

I've solved most of my problems by typing each code into the "Search" function and finding out what others have done to fix each code. For example, a 214 code could be a bad CID sensor or maybe a bad DIS sensor.

 

[rubydist]

114 ACT out of self-test range.
556 Fuel pump primary circuit failure.
214 CID circuit failure.
121 Throttle position (TP) sensor out of self-test range.

556 is set on these cars when the engine stalls, and can be ignored.

the tps and act are on the same section of harness, and the fact that you have them both at the same time (and both are out of range issues) suggests a wiring issue - I would check the connectors and ground on that section of the harness.

the car will not run right with either of the 114 or the 121, so you need to figure those out - I would start there. neither are expensive, so you might just try replacing both.

214 is either the cam sensor (most likely) or possibly the dis. the cam sensor is not expensive, so I would replace it.

does the tach jump around when the car is running rough? if the cam sensor is sick, it can cause timing issues, make the tach jump around, and result in a very poorly running engine. you can disconnect the cam sensor without issue, except that it will make the pcm have to guess which cylinder is at tdc, so it will typically take 2-3 cranking tries to get it to start.

with the tps acting up, once the engine switches from open loop at startup to closed loop a little later, the engine will not run right either.

and I have never seen a SHO motor run right with an act code present. symptoms vary widely, but it will basically run very poorly.

 

[nerflhopper]

Thank you all for your replies. The boy and I are otherwise employed, so we'll be looking at it again as soon as we have a moment free. I'll keep you all posted. Zoomlater, happy to see your in the Seattle area...could come in handy someday