MAP Sensor issues

[Trstrugar]

My truck is a 1994 GMC k1500 with a 5.7l. I am throwing a code 33 for a map sensor. The truck has rough start up for about 10 seconds and then it seems to run fine. When I unplug the sensor it starts up fine, but runs extraordinarily rich. I replaced the sensor and it didn't make a difference so I don't think it's the sensor itself. TYIA

 

[Heath Andrews]

My truck is a 1994 GMC k1500 with a 5.7l. I am throwing a code 33 for a map sensor. The truck has rough start up for about 10 seconds and then it seems to run fine. When I unplug the sensor it starts up fine, but runs extraordinarily rich. I replaced the sensor and it didn't make a difference so I don't think it's the sensor itself. TYIA

Check the PCM itself, the connections and then you idle air control valve. If still doing it start checking all of the under hood sensors, connections and your pcv valve. The 350 in the mid nineties can be temperamental, but usually more in the high mileage.

 

[SwatDawg15]

My truck is a 1994 GMC k1500 with a 5.7l. I am throwing a code 33 for a map sensor. The truck has rough start up for about 10 seconds and then it seems to run fine. When I unplug the sensor it starts up fine, but runs extraordinarily rich. I replaced the sensor and it didn't make a difference so I don't think it's the sensor itself. TYIA

As stated above check the IAC and harness. Also the temp sensor by the T-stat housing.

 

[Trstrugar]

I fixed this issue. the vacuum line was just not connected to the tbi, it was instead connected to the egr bleed valve. Put them in their right places and now runs correctly!

 

[blazer9490]

Can you post a picture of the correct routing for me? My 94 blazer is doing the same exact thing running very rich with map plugged in or not though

 

[someotherguy]

MAP sensor connects to the port near the bottom rear of the TBI. It's the only port back there. It's not uncommon for the rubber boot on the plastic line to become cracked and loose.

Richard