Just bought my first Blazer a couple weeks ago, a '97 V-6. Having a "service engine" light and shifts hard going into 2nd.

Getting a P0122 code, low TPS voltage. I found out TPS was unplugged, reconnected and Blazer wants to die when I touch gas pedal, but no code.

I replaced TPS and disconnected battery for about 20 min, can accelerate slowly fine, but wants to die if I hit pedal hard....also, shifts normal.

Until yesterday morning...... Won't start, unless I unplug TPS. Only code I ever get is P0122 when it's unplugged.

Parts store guy said it could be a short in TPS wires. Voltage reads 5V in and increases up to 4.7 coming out. If it is wire, where does the blue wire (mine is green) connect to PCM?

Any other suggestions?

 

The wiring diagram (including pin locations) is provided in the trouble code sheet:
P0122 - Throttle Position Sensor Circuit Low Voltage

You need to verify that the sensor return is within spec as well. Unplugging the TPS sensor could put the PCM into open loop operation where it may be ignoring the values from other sensors. Monitoring sensor information should tell you which sensor is the culprit.

 

Pin 24 on black side on PCM has gray wire running to it, white side is blank. Could it change color somewhere? It doesn't look like anything has been replaced in harness, all tape is old.

I tested the return, I can't remember the exact numbers, but it started out around 1 volt and opening throttle it slowly climbs to near 5 at max.

When TPS is connected, I don't get any codes. Drove it a couple miles with reader attached and got no codes. Thought it may be a small problem with EGR or MAF, disconnected one at a time and they coded, so reconnected.


Getting horrible mileage, and need to fix it quick. Have to make an emergency 600 mile round-trip in next few days for a funeral

 

When was the last time a full tune up was performed?

To get to the bottom of this, you are going to have to find someone with a full feature scan tool and who knows what the sensor values are supposed to be. As I stated, if there are no codes, you have to look at the live data and see what sensor is flaking out, then determine why.

 

Not sure, but going to try tune-up today.

Here is a link to the scanner I have, will it give me the info I need? I can get a freeze frame, if that helps.
OBD II / EOBD Code Scanner

With TPS unplugged, I get:
DTC P0122
MAP 9.5kPa
MAF .254g/s
plus fuel info, coolant temp, etc.

I/M readiness
I have INC's on catalyst mon, evap sys, oxygen sensor, and EGR.
Does this help any?

 

The description of the scan tool states that it can graph data... You need to look for wide swings in MAP/MAF/TPS values at steady speeds/throttle positions. The O2s should swing back and forth in response to IPW changes on B1 & B2.

Without a lot of other information, those values listed really are meaningless.

Have you gone through the typical DIY cleanings of things? Throttle body (including IAC valve)? MAF? EGR? All of these are covered in the how-to articles found in the Tech Article (DIY) section (click on the index in my signature).

 

This is similar to what happened to me a while back. I turned out a sensor unrelated to the TPS was shorting out intermittedly. While doing a live scan, watch to see if any sensors values go to zero. There are about 7 sensors that share the 5 volt reference voltage that the wiring diagram shows. If a sensor shorts to ground it kills that 5 volt reference. The hard shift is possibly related to the same problem.