Fuching DJet issues *SOLVED*, Running out of things to try Options

[rjames]

Last summer all of a sudden my car wouldn’t stay running. If I could get it started the idle would hunt and the car would die unless I kept on the gas. Lack of power at times. All somewhat erratic.
Found that the MPS wouldn’t hold vacuum.

Replaced the bad mps with a known good one. Car idles high when cold (higher than I think it should ~1600 rpm) so AAR is good, then when it warms up idle hunts from ~900rpm to the point where it almost dies unless I open the throttle body bleed screw quite a bit and turn the ECU knob just a few clicks away from full clockwise.

So I did the following hoping to fix the issue:
Replaced all vac hoses including intake runner to plenum hoses.
New intakecrunner gaskets
Verified plenum isn’t leaking
New throttle body gasket
Installed NOS throttle body
Rebuilt the distributor
New condenser
Rebuilt injectors and flow tested
New fuel lines
Fuel pump is less than 2 years old
Set timing and dwell with advance disconnected
New CHT (resistance reads 1.7 w/engine off @70 degrees in the garage)
Calibrated the TPS, even unplugged it to take it out of the equation, didn’t change anything.
ECU matches the MPS (both correct part #s for a ‘75 2.0)
Tried a known good ECU from a ‘74, no change.

Feels like the MPS needs to be calibrated...but then again, these are all the same symptoms I had with the old bad mps. Replacement mps is from a Jeff B and was tested, but I haven’t retested it to see if it’s holding vacuum.
(Don’t have the necessary tool, but maybe that’s the next step)

Help! What am I missing?

[JeffBowlsby]

Its frequently the case when the MPS is going bad...that the system has been adjusted to compensate for a failing MPS. Then when the new good MPS is installed...the system itself is not in adjustment and seems wrong. Fuel pressure is changed, the air bleed screw is changed, the ECU idle mixture knob is changed and who knows what else.

For example, it was not mentioned above that the fuel pressure was checked. Its basic and important so use a gauge and check it. Then balance idle sped with the air bleed screw when warm.

Is the cold start valve leaking? Test it or take it out of the system.


Are there any vacuum leaks...gaskets, fuel injector tip seals, the air plenum etc.?

All these can affect idle and mixture.

[rjames]

Its frequently the case when the MPS is going bad...that the system has been adjusted to compensate for a failing MPS. Then when the new good MPS is installed...the system itself is not in adjustment and seems wrong. Fuel pressure is changed, the air bleed screw is changed, the ECU idle mixture knob is changed and who knows what else.

For example, it was not mentioned above that the fuel pressure was checked. Its basic and important so use a gauge and check it. Then balance idle sped with the air bleed screw when warm.

Is the cold start valve leaking? Test it or take it out of the system.


Are there any vacuum leaks...gaskets, fuel injector tip seals, the air plenum etc.?

All these can affect idle and mixture.

No vacuum leaks detected. see above for all of the items that have been replaced and/or checked already.

Cold start valve has been removed from the system to no effect.
Besides the bleed screw on the TB and the ecu knob, and fuel pressure, is there something else that could be adjusted for a failing MPS that would make the car undriveable with a good MPS? (All inection components are stock.)

Fuel pressure is on the list to check next.
Distributer is still in question.
MPS is still in question.
Wiring harness possibly, but seems unlikely.

Symptoms originally occurred when the MPS went bad. Seems unlikely that something would’ve happened to the wiring harness, distributor, or fuel pump/pressure or wiring harness at the same time.