I have been trying to lick a hunting idle and had my original MPS tested with a mityvac. It started to leak down at 10 in/hg so I purchased a used one (same part #) that had good vacuum. I have installed it but now I can't get the car started. The ECU knob has been turned all the way CW so I presume the idle adjustment was adjusted to compensate. When I reinstall my original unit the car will start but still hunts. This is a '73 1.7L with the original d-jet FI. It usually starts first turn of the key and idles about 1600 until the AAR closes, then hunts from 1600 to stall if I don't give it gas. After it gets good and warm idle settles down to about 900 but still hunts. All the vacuum hoses have been replaced and I have sprayed carb cleaner in all the suspect areas without a response. Is there anything I should do since I am intoducing a different MPS into the system? I purchased the used MPS from a reputable seller who will refund if I desire but I would love to make it work.

Thanks for any help.

Did you check the coils on the new MPS to see if they are good? Check them with a voltmeter and see if they are working. The unit may hold vacuum, but if the colis down work, then the ECU wont get a signal. Did you pull an injector and see if you are getting any squirts?

Shot in the dark here, but you might also want to try adjusting the mixture on the ECU back within a normal range with the new MPS. It may not be getting enough fuel at cranking speed. Again, this is just a shot in the dark, as my car is a '70 and doesn't have the idle mixture screw on the ECU.
Mark D.

good start, normalize the idle

In 1973 the ECU and MPS are specific and cannot be paired with any other parts. So that means you need the correct one for that specific ECU.
At the top of the page, go to 914info, then to "links to other 914 sites"
You will see Brad Anders page on Djet.
He lists the correct ECU number and MPS number for your car.

The 1973 thing set a light off in my head. You may have replaced it with a part that was the same as before, but it costs nothing to verify that you have the correct parts to start with...it would save time.

When the MPS goes bad, you go to a full rich condition.
So, if your car is not starting, and you have a presumed good "new" MPS unit, you may have a super lean condition.

This could be caused by a bad or shorted Head Tempo Sensor (CHT)
Or Temp Sensor number 2...

Look on Brads site for the correct readings, test your CHT when cold.
If you unplug it you can start the car, but it will run poorly.

Rich