MAP Sensor

[Tazman]

A couple weeks ago my engine stumbled a little while doing 45 mph with the air on.The check engine light came on so when I got home I checked it and a code 33 came up which is the map sensor sending a low idle message.It did it again a few days later so I decided to replace the MAP sensor.After doing so it ran great as it usually does but it did it again.I am at ends trying to figure this out.I do not see how it could be electrical or vacuum because it does not do it all the time.I will keep looking but just wondered if any one out there had any ideas.Thanks

[Captkaos]

Is the Hose going to it ok?

[bd]

Code 33 is high MAP signal voltage (low manifold vacuum).

Many intermittent drivability problems result from poor electrical connections.  Assuming the 87, check/clean/tighten terminal connections at the MAP sensor and ECM cavities C14 (gray: 5-v reference), C11 (light green: MAP signal), and A11 or D2 (purple: MAP ground).

If the vacuum hose mentioned by Captkaos and the electrical connections are fine, check the EGR valve.  The EGR valves on these trucks have a high incidence of failure from intermittently hanging open, causing low manifold vacuum.  You can take the EGR valve off, turn it upside down and dribble a small amount of solvent around the pintle valve & seat.  Watch through the adjacent port to see if fluid leaks past the closed pintle.

If all the above checks out okay, you could tee a vacuum gauge into the MAP sensor hose and drive it that way until it acts up - then take a peek at the gauge to see if low manifold vacuum is occurring and proceed from there.

[Tazman]

I did check the hose going to the sensor and it is fine.The EGR valve is new but I will check it out like you say and will see what I find out.Thanks