Idle speed issues

[flat4]

Hi there. Have a 75 2.0 DJet that has a hanging idle (1300-1400). I closed the e bypass screw and no change. Reset the timing to 27 degrees, calibrated the TPS and nada.

I tried clamping off the different vacuum hoses one at a time, and the only one that made a difference was the MAP to plenum hose. Clamping it caused a drop in idle.

Only thing of note is a clacky injector on #2. Not sure if they would cause a fast idle though.

Open to ideas.

[Dave at Pelican Parts]

When you reset the timing, was that at 3500 RPM? Can you check that the timing dials back near TDC when you let off the throttle? Overly advanced timing will raise your idle.

Do you have access to a smoke machine? Can you fabricate one? Blow smoke into the intake with the engine off and see if you can spot leaks.

--DD

[Lockwodo]

If your car has an auxiliary air regulator (AAR) it could be stuck open. Also, if by MAP sensor you mean the Manifold Pressure Sensor, it should hold a vacuum so if clamping the line to the plenum reduces idle, I would suspect a leaking diaphragm in the MPS.

[flat4]

Good day. So I swapped out the MPS and no real difference. I took the car for a drive and it started out sputtering and jerking around 2800-3000 rpm.
After a few min, the problem went away (for the most part).

I swapped the old MPS back in, and it’s a different experience. It has what feels like a flat spot off idle and is relatively smooth after that.

Idle is still high.

[Lockwodo]

If the runability changes when you swap one MPS for another, and assuming that's all you did, then it's certainly possible that both MPSs are bad. The right way to test an MPS is to use a hand vacuum pump with a gauge and attach it to the sensing port on the MPS and pull a vacuum of 10 inches of mercury, then observe whether it loses vacuum over a few minute period. If it does, then the MPS diaphragm is defective.

The high idle indicates a vacuum leak.