I think the closest zener is going to be 4.7 volt.

Not sure what the output impeadence/drive capability of the MAP sensor is but there may be an issue with the zener clamp current, depending on what diode you use. I believe the EEC-IV inputs are BJTs with input impeadence in the 10's of kohm range so it will only ask the sensor for 1ma or so. most zeners need way more current than that to hold there voltage rating (4.7volts or whatever)

I went with the ITP OBA because it is proven, simple and I didn't want to hack up the factory wiring.

Now, if you really wanted to over engineer a voltage clamp with nano second delay, use a mircrocontroller with a A/D & D/A converters and write some software