I've been scratching my head for days trying to figure out this problem. A few days ago while my son was driving the blazer when it started idling rough and the SES light came on so he went by Autozone and they checked it and it said it was a loose gas cap, so they tighted it up and it fixed the problem. The next day it done it again so we replaced the cap and this time the problem continued. I plugged it up and checked the code and it was the P0440 EVAP, so I pulled the canister out and checked the lines which were ok and I replaced a couple of lines at the purge solenoid then cleared the codes and started the engine, it was still running rough. I then checked the codes again, this time it was the P0122 code. I have checked the voltage on the TPS, it had 5v on one wire an the other one was .8 with the throttle closed and went to 4.7v with the throttle open. I went ahead and replaced the sensor but it still runs rough, I also checked the voltage at the MAP sensor and the EGR and they both have 5v going to them and checked the wiring as best as I could to see if it was grounded out anywhere and did not see anything wrong. I cleared the codes again and restarted the blazer and now I am getting P0107, P0122 and P0123, do you guys have any suggestions? btw, I replaced the fuel pump and fuel pressure regulator about 9 months ago.

 

Codes:
P0107 - Manifold Absolute Pressure [MAP] Sensor Circuit Low Voltage
P0122 - Throttle Position Sensor Circuit Low Voltage
P0123 - Throttle Position Sensor Circuit High Voltage

These sensors all utilize the +5V reference from the PCM. You may have a problem with the wiring from the PCM to these sensors that is causing voltage fluctuations.

 

The blazer drives good once you get the RPM's up, I unplugged the TPS and the idle went up and the engine smoothed out, but at idle it runs rough and runs very rich.

 

If the MAP sensor isn't reading properly, your PCM won't be able to accurately deliver the fuel. Diagnosing the codes in conjunction with each other (comparing the trouble shooting steps, wiring, etc) is what is needed. I suspect a common problem is causing your troubles.

 

Thanks, I appreciate the help!

 

Well, it ended up being a stuck EGR...I guess I should have started there first! Thanks for the imput!