Hi my name is XXXXX XXXXX Your complete satisfaction is my goal. Please provide as much information about your concern as you can.
Are there any trouble codes setting? 14, 15, 33, 34,45? Have you checked the EGR valve for being stuck open slightly?
I would inspect the EGR valve, and also relocate the MAP sensor hose from the rear of the throttle body to another manifold vacuum source.
Next I would inspect the coolant temp sensor circuit for the ECM. if it is open or has high resistance, it will read , like the engine is cold, and the ECM will deliver fuel, like it is a cold start, and this will be too much when the engine is warm.
Try disconnecting the o2 sensor. if it runs better, then you may have an o2 sensor that is reading lean all the time. also inspect the o2 sensor wire to make sure it is not shorted to ground. this also will tell the computer to give the engine more fuel.
If you need more information, let me know.
Do you have a scan tool to get some readings from the ECM so I can see what is going on with the fuel control?
I need block learn readings, and o2 sensor reading, coolant temp readings, TPS reading, and MAP sensor reading.
I need to see what the computer sees, to find out what is going on here.
Have you verified good power and ground to ECM. Use a voltage drop test to verify ground from the ECM to the engine. Connections at the thermostat housing can get corroded and still be tight. If no codes are setting, I want you to disconnect the TPS and see if it will set a code for the TPS. we have to see if the diagnostics are capable of working. The TPS is the fastest code to set when disconnected and should set immediately.
Also check the distributor shaft. If the shaft gets worn it will wobble inside the housing and give an inaccurate rpm signal to the ECM ( this was a very common concern in these years on a 454.)
What kind of scan tool are you using?
Is it the genesis scanner? Doesn't matter, it will work just fine.. I sorry i did not read that you had replaced the distributor already. Do you need a diagram of the ECM connector to do the voltage drop test?
You can get back to me by responding to this question.
I have to get offline soon, we are having severe weather now and the power is kicking on and off, I had to restart my computer to respond to you. I will be back online later this afternoon if you need more info before Monday.
Here is the ECM diagrams for a 89 7.4V8 throttle body. Let me know , if you need more information.