Mercury 175 EFI 1989

by Steve
(Monticello, KY)

I'm experiencing a problem at idle both in neutral and in gear. The idle is rough and engine does not change when both center cylinder plug wires are removed although spark is present. When the throttle is pushed down the engine bogs to a minor extent then "catches" and runs great. This motor has the oil injection system removed.

Here's what has been done thus far:

1. Compression is good on all cylinders
2. All fuel and vacuum lines checked
3. New spark plugs installed
4. Pulse fuel pump rebuilt
5. New electric fuel pump installed
6. Injectors removed and cleaned
7. Injectors tested by adding current to each with spray observed
8. Disconnecting temperature sensor causes engine rpm to drop

I'm scratching my head at this point and cannot figure this one out. Any ideas?