Nissan Repair: slipping in and out of overdrive, mass airflow sensor, upper radiator hose

Question
QUESTION: I have an 88 Nissan Pulsar, with the ca18det engine.  When on the highway, it seems to go in and out of overdrive no matter the terrain or throttle.  Is this a vacuum controlled component of the tranny?  Other info:  I recently replaced 3 coil packs after the engine overheated due to the upper radiator hose splitting.  the heat under the hood caused half of a relay box (by the battery) to melt as well as some contraption hooked between the air cleaner and what I belive is the EGR.  Any advice appreciated

ANSWER: Nate,

Correct the EGR control module to make sure it is not leaking vacuum.  A vacuum leak will cause the problem you describe.  So, look for vacuum leaks since there is a sensor that lets the computer know you are not getting on the engine.  No vacuum means you are pushing the gas and it will come out of overdrive.  So, you will need to look for a rotten or cracked vacuum line.

---------- FOLLOW-UP ----------

QUESTION: Vacuum line looks good, but the orifice on the EGR looks plugged up (or is it really small?).  Since I have it back on the road for my commute (about 55 miles each way), I am noticing it happens more in the morning than in the evening.  Should I replace the EGR?

Answer
Nate,

Remove the EGR and clean the passage and verify that the unit works off the vehicle.  And, be sure to check all of the vacuum lines while it is off the vehicle.  A line can be compromised where you cannot see it and that will screw up the works.  Also, check the intake hose clamps and to make sure there are no cracks or leaks on the intake hose from the mass airflow sensor to the throttle body.