Pulsing At Idle Options

[Jim C]

Want to see what the World thinks of this. I have a 1976 2.0 with FI. Injectors have been cleaned and checked, ECU repaired, CO checked, trigger points replaced, valves adjusted, timing set, but at idle it goes from barely running to 1000 RPM or so in a rhythmic manner. Also, when accelerating you can feel a momentary drop in power. Thoughts? (IMG:style_emoticons/default/confused24.gif)

[Jim C]

Want to see what the World thinks of this. I have a 1976 2.0 with FI. Injectors have been cleaned and checked, ECU repaired, CO checked, trigger points replaced, valves adjusted, timing set, but at idle it goes from barely running to 1000 RPM or so in a rhythmic manner. Also, when accelerating you can feel a momentary drop in power. Thoughts? (IMG:style_emoticons/default/confused24.gif)

Any prime suspects for the leak?

[BeatNavy]

Want to see what the World thinks of this. I have a 1976 2.0 with FI. Injectors have been cleaned and checked, ECU repaired, CO checked, trigger points replaced, valves adjusted, timing set, but at idle it goes from barely running to 1000 RPM or so in a rhythmic manner. Also, when accelerating you can feel a momentary drop in power. Thoughts? (IMG:style_emoticons/default/confused24.gif)

Any prime suspects for the leak?

I would have said something is making you run lean, but here's some info straight from the Anders D-Jet Troubleshooting Page: https://members.rennlist.com/pbanders/DJetParts.htm#Vacuum Leaks

Vacuum Leaks - Find 'em and Fix 'em!
Probably one of the most common problem with D-Jetronic systems is a vacuum leak. Unlike in L-Jetronic, vacuum leaks do not cause a lean mixture condition, but instead cause high idle and idle instability. The problem with finding vacuum leaks is that there are so many sources! Below is a list of some of the more common leak sources:
Vacuum hoses: Hoses should be replaced every 5 years. They lose elasticity when fitted, hardening and eventually cracking. Replace the entire set with a new set.
Manifold Pressure Sensor: Cracked diaphragm, leaky case.
Injector seals: Leaks due to hardening and cracking.
Intake manifold gaskets: Cracked, poorly sealed and/or torqued.
Intake runner boots: Leaks due to hardening and cracking.
Intake manifold (plenum): Can have leaks due to seam cracks and cracks around other fittings.
Cold start valve: Leaks from the valve itself and the seal to the plenum.
Throttle body seal: Missing or cracked gasket to the plenum.
Throttle body shaft: Worn shaft leaks air past the throttle plate.
Auxiliary air regulator: Stuck open, defective valve
Deceleration valve: Stuck open, or leak in the control diaphragm
Distributor advance/retard: Either or both the advance and retard diaphragms cracked or leaky
PCV Valve: Stuck open or worn out.
There are various ways to detect these types of leaks. Visual inspection is your most powerful tool, I'm loathe to suggest any other way (e.g. spraying "something" on the suspected part that gets sucked in and changes the idle speed) due to liability concerns.

[JamesM]

I would have said something is making you run lean

(IMG:style_emoticons/default/agree.gif) Not sure it would be a vacuum leak though as that would normally cause high idle on a d-jet car.

What does your fuel pressure look like? and what happens when you richen the idle mixture adjustment on the ECU? It your throttle position sensor good?

[alexkirkham]

I would have said something is making you run lean

(IMG:style_emoticons/default/agree.gif) Not sure it would be a vacuum leak though as that would normally cause high idle on a d-jet car.

What does your fuel pressure look like? and what happens when you richen the idle mixture adjustment on the ECU? It your throttle position sensor good?

I have a broad band O2 sensor on my exhaust but otherwise stock D jet. This has been the single most useful thing I've ever done to the car. I can fiddle with the fuel pressure, idle knob and TPS to dial everything in. And it's completely predictable that whenever there is a lean condition for idle (eg hot start) the cycling starts. And when the AFR goes below 14 it stops. So that would be my guess.... Vacuum leaks can easily cause a lean condition, it just depends where they are...

[dr914@autoatlanta.com]

that is an excellent thing that you did

I would have said something is making you run lean

(IMG:style_emoticons/default/agree.gif) Not sure it would be a vacuum leak though as that would normally cause high idle on a d-jet car.

What does your fuel pressure look like? and what happens when you richen the idle mixture adjustment on the ECU? It your throttle position sensor good?

I have a broad band O2 sensor on my exhaust but otherwise stock D jet. This has been the single most useful thing I've ever done to the car. I can fiddle with the fuel pressure, idle knob and TPS to dial everything in. And it's completely predictable that whenever there is a lean condition for idle (eg hot start) the cycling starts. And when the AFR goes below 14 it stops. So that would be my guess.... Vacuum leaks can easily cause a lean condition, it just depends where they are...