Completed rebuild on 1974 914 2.0 L. All fuel and vacuum lines are also new. Engine idle varies between 1000 and 2000 rpm every few seconds what could cause this?

Did you rebuild the throttle body?

Most of them are worn creating a vacuum leak

Also worth servicing the distributor
Or just replacing with 123

Start here - this is the foundation of all things DJet

That is interesting, there are not any feedback mechanisms in the djet, so idle fluctuation is a weird one to me. How much time are you talking about between fluctuations?

I'm going to go with throttle body as the prime suspect.

Build a smoke machine and test your intake tract! Or buy a cheap one off Amazon. They are incredibly helpful at finding air leaks.

Zach

Known as ‘hunting’? Up and down? Examine the stacked elbow. Cracks can hide.

You have an uncontrolled vacuum leak somewhere downstream of the throttle body. That's why it has a "hunting" idle. Check the rubber elbow for cracks, as well as check the plenum seams for leaks using propane or carb cleaner.

Plenum cloth connectors got me before.

[quote name='brant' date='Feb 6 2025, 08:34 AM' post='3190560']
Did you rebuild the throttle body?

Most of them are worn creating a vacuum leak

Also worth servicing the distributor
Or just replacing with 123
[/quote/

I agree.
When I rebuilt my Throttle Body & added 123 my engine issues are gone.
Tom

I hope that you will expand on your answer. How do the dizzy and throttle body feed into this? Anything that I can learn about the little fellers is a bonus. Thanks.

Hunting normally isn't the result of a vacuum leak. A djet doesn't hunt if you crack the throttle or the aar is open. It might be due to your timing or a temp sensor sending strange signals. Running from 1k to 2k is a very large amount of air. You can hear the aar and that only brings you to 1.4k.

I'll take a stab at an answer Worn....


so the TB has the TPS which is how it is calibrated.
the TPS knows when the butterfly is closed, and thus how much air should be entering the intake ... when the butterfly is worn out... air enters arounds the sides of it.

and also... the calibration becomes wrong. as the units of air it is expecting (very little, just the hole in the butterfly at idle) when in reality on a worn out TB, you are getting more units of air than the TPS thinks... that is an unmettered vacuum leak

regarding the dizzy. it has the points plates which slide or rotate and change the timing. those plates need to slide easily. easily enough for the vacuum canister to advance or retard the timing slightly as the centifugal weights pull it in a direction with rpm.

some of these stick... also I've had very worn plates on cars. with a worn or stuck plate they are not returning or opening smoothly ... any time timing is changed, so does rpm.


short answer.
but 2 of the most common causes of surging idle
and not surprising as these parts are 50 years old.

2K is a pretty high idle. I would want to verify the accurate and correct timing. and then I'd expect to find more vacuum leaks for such a high idle.

brant

Dup

add to that the butterfly shaft and bushings.

I hope you’re doing GREAT. Kent
It’s been a while
Hope to see you soon

I would go with a leak like brant described if it were not fluctuating, the op still hasn't cleared up the interval and whether it is hunting or just random. If it's just "I came to a stop and this time it's at 2k" or if it is bouncing between 1k and 2k. Maybe I missed that post.

A hunting idle can also be caused by a lean idle mixture.

Try rotating the mixture knob on the ECU full clockwise and see if it makes a difference.

Ahh yes, now that would do it.

Thank for all the feedback on the idle searching problem. The searching starts as the cold idle ends. The fluctuation is back and forth every few seconds. I have not driven since rebuild. Only did the cam break in. I did clean the throttle body and distributor, but did not do any rebuilds on these items. I did just complete brake system rebuild and should be able to drive soon. Some had mentioned the rubber vacuum which is new. I also tried adjusting the ECU, but not sure of the proper techniqueClick to view attachment

remind me, was it modded at all? I bet you are just running lean after you warm up. After my 2056 I had to retune the MPS and change the ECU idle mix. A quick test is as mention above, just turn the knob on the ECU to richen the idle mix, if it goes away then you know that is your problem and you better take a look at your mix across the board before driving it much. Don't want to drop a seat/burn a valve etc.

Beautiful Paint Job - do you have a color number? Is it an original color?

Can anyone reccomend someone who is currently rebuilding 914 2.0L throttle bodies?

Mark did mine.

Bartlett 914 is his name on here. PM him.

^^^That

But I suspect it is just part of the problem and there are multiple contributing factors.

D-jet idle can be sort of tricky where you have to chase multiple variables simultaneously to get it just right.

My suspicion is you have a combination of ALL the following happening at the same time to some extent.

1. Intake air leak(s)
2. Lean mixture
3. A worn out distributor. or possibly the wrong distributor or misadjusted timing.


I would start by checking the timing and verifying that your vacuum retard is functioning properly. 74 2.0s absolutely require proper functioning vacuum retard to idle properly. Next check what the timing is doing when it is hunting. If you have weak advance springs a small air leak can be enough to get you up to speed to where a bunch of unintended ignition advance then revs you up even higher, at least until it starves itself and drops back down.

long story short, with d-jet you sort of have to check everything, but start with timing and then air leaks.

I had a hunting idle and it went away when I replaed the Manifold Pressure Sensor MPS with a correct untampered one. Cross check your MPS part number and make sure it is correct for your model.

Also, if you look super close at the space down and around your ECU knob, you will see a melted spot in the plastic. That is the factory calibration point for the ECU knob pointer.

Massive D-Jet info here https://members.rennlist.com/pbanders/DJetParts.htm