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)

[76-914]

Vacuum leak.

[dr914@autoatlanta.com]

I second that

Vacuum leak.

[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.

[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?

Wow. Guess I better get cracking!

[Literati914]

Isn't there anything you can run thru the engine that'll manifest into a visual (smoke, dye) to pin point the leak.. seafoam for example?

[Bleyseng]

I spray starting fluid in small amounts

[saigon71]

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)

Absolutely check for vacuum leaks first. But based on this:

"Also, when accelerating you can feel a momentary drop in power. Thoughts?"

I would also check the calibration of your throttle position sensor. If the sensor isn't set properly, it can cause the car to lose power just as you crack the throttle.

Other:

Try richening the idle mixture by adjusting the mixture knob on your ECU clockwise a click at a time.

[Jim C]

I checked the vacuum hoses and replaced those that were questionable. I noticed that the vacuum advance on the distro was plugged and the vacuum retard not connected. The web said both that you needed the vacuum advance and that you didn't need the vacuum advance with a Pertronix. I figured it could hurt to reestablish those connections, so I did. I started the car and it was a miracle! Smooth idle at a bit over 1000 rpm vice hunting between 500 and 0. Step on gas and no hesitation. It never sounded so good! Took it out on the road. Beautiful until I shifted into third about a 1/4 of a mile from home and there was bucking and power loss. What have I done? What more do I need to go after? (IMG:style_emoticons/default/sad.gif)

[Jim C]

I checked the vacuum hoses and replaced those that were questionable. I noticed that the vacuum advance on the distro was plugged and the vacuum retard not connected. The web said both that you needed the vacuum advance and that you didn't need the vacuum advance with a Pertronix. I figured it could hurt to reestablish those connections, so I did. I started the car and it was a miracle! Smooth idle at a bit over 1000 rpm vice hunting between 500 and 0. Step on gas and no hesitation. It never sounded so good! Took it out on the road. Beautiful until I shifted into third about a 1/4 of a mile from home and there was bucking and power loss. What have I done? What more do I need to go after? (IMG:style_emoticons/default/sad.gif)

Meant to say couldn't hurt to reestablish

[Bleyseng]

Put a few drops of oil in the center shaft of the dizzy after removing the rotor. The mechancial advance weights have a factory grease on them that hardens over time and they need to be oiled to operate smoothly.

or you still have a vacuum leak and are running lean

[rjames]

Have you tried adjusting the knob on your ECU? Try turning it clockwise a couple of clicks. EDIT- just saw that saigon71 suggested the same thing. I'd Also follow his advice to check the TPS and if the tracks look good, recalibrate it as I've read that if it's not set properly it can affect the idle.

It's true that a vacuum leak will mess with the idle, but it would then likely idle high. If it's not going above 1000rpms at idle and it bogs down when you step on the gas, the air/fuel ratio could be off.

What's the history on this car? Is there signs that the MPS has been opened up?

After making sure all of the hoses are connected correctly, I'd check these first because they are the easiest to do:
Adjust ECU knob,
Check MPS to see if it holds vacuum
Check distributor vacuum canister to see if it holds vacuum
Check TPS to see if it's worn & calibrate it correctly

[StarBear]

Isn't there anything you can run thru the engine that'll manifest into a visual (smoke, dye) to pin point the leak.. seafoam for example?

I use a hobo method - get 2-3 sticks of incense going, bundled together. Creates a light "smoke" (and pleasant smelling) - where the smoke gets sucked in there's a leak. Also confirms air intake strength, too. Just don't let the ashes drop.

[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?

[JeffBowlsby]

Isn't there anything you can run thru the engine that'll manifest into a visual (smoke, dye) to pin point the leak.. seafoam for example?

Try this - engine off. Duct tape your leaf blower to the tailpipe airtight and turn it on. Check for leaks in the engine bay with a smoke pencil or a soapy solution.

The opposite method would use a shop vac at the tailpipe, and a smoke pencil to look for intake leaks.

The air plenum under the throttle body is a known common leak, at the support tubes where they penetrate through the plenum. Hard to find without removing the plenum.

[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...