‘74 1.8L L-Jetronic idle hang… SOLVED!, Thanks everyone! Options

[Van B]

Evening everyone. So, I installed the proper intake boot from auto Atlanta this afternoon but the car still isn’t behaving properly.
Basically, when the car is warm and I go from driving at speed to a stop, the rpm hangs around 1600-1800. Once stopped, I can sometimes blip the throttle and get it to fall to around 1100rpm. If I load the engine by partially releasing the clutch, I can get the car to idle normally at 800-ish and it stays there.
Also, there is no hunting, surging, or problems with idling over a long term.
I just can’t understand why it hangs when I’m out driving.

I’ll run through the things I’ve checked so far and hopefully someone with more experience can help.

First I took off the Aux Air Regulator and confirmed it is functional.

Replaced the boot and discovered the one installed was not correct for a 74 1.8L
- that meant I had to replace and sort out some vacuum lines that were not correct length and get a substitute for the small fitting on the boot.

Put clamps on connections that didn’t seem tight enough.

Had the car smoke tested when I bought it and the mechanic said the boot was the only thing leaking.

Could the barn door on the AFM be hanging up or too loose?

Thanks!

Van

[wonkipop]

did your mechanic tell you where the boot was leaking?

there are four connection points. (IMG:style_emoticons/default/beerchug.gif)

[Van B]

All over. It was old and cracked to hell. But like I said, that’s all new and sorted as of this afternoon.

[ndfrigi]

maybe flap inside throttle is dirty, or return spring or your gas pedal sticking.

[SteveL]

I have experienced this same issue, 74 1.8 L-Jet.
Sorry, don't have the answer, but interested as heck at what you get for replies.
Thinking about it, since I replaced all vacuum hoses, I haven't noticed it happening.....

[wonkipop]

All over. It was old and cracked to hell. But like I said, that’s all new and sorted as of this afternoon.

sorry. thought you meant you had replaced it and it was still leaking. (IMG:style_emoticons/default/beerchug.gif)


could be the afm.

could also be decel valve sticking? not sure.

as suggested above mechanically the throttle is not returning to fully closed and is hanging up either at the throttle or back at the pedals. lubricate.
moving the clutch and having an effect might be pointing to something?

check one thing at a time and test run it.

you can check the decel valve by disconnecting the hoses to it and plugging the hoses.
drive it and see it it returns to idle. decel slows down the return to idle for emissions.

you can also check your aav, even though you say you have cleaned it out.
once you have it warmed up and are driving it and it sticks at high revs, see if while its stuck at high revs if you pinch the hose feeding into the aav from the intake boot whether anything happens.

someone here would know a bit more about worn afms.

[emerygt350]

I had the same idle hang on my 2.0 djet (and posted about it). I found it to be a pile of problems. Dirty pcv, which I don't think you have, combined with sticking advance and retard plate, which I think you may have.

If you have vacuum retard, check the line, check the diaphragm, and then clean and lubricate the retard plate in the distributor.

[timothy_nd28]

Really sounds like something is going on with your throttle body, more specifically the idle circuit control switch. This switch may be intermittently not closing when at idle.

Pretty easy to test, unplug the ECU connector and put your meter leads (set for resistance) on pins 2 and 18. I would set the meter so it would beep when it senses continuity. Jump in the car and play with the accelerator pedal, make sure you hear beeps everytime you let go of the throttle.

I'm not sure how much you are a stickler for originality, but I recently ditched my throttle body and replaced it with a Gowesty throttle body. Some modifications needed, but man what a difference it made.

[Van B]

Ok, lots of things for me to look at then lol. I’m new to the car and flying blind with no manual or other 914 guys around me.

Wonkipop,
Where is the decel valve? I’m doing this with no manual and I’ve only had the car two week so, hopefully you guys can give me some talk-ons?

Emery,
I don’t think I’m ready to mess with the distributor yet. I haven’t had a car with a cap in about 25yrs and I don’t have anything to retime the car. I do have a diaphragm on the distributor though so I’ll unplug and blow out all the lines. At least that will remove one variable.

Tim,
Uh you got anything to show me what the PIN numbers are? Otherwise, I think this might be outside my ability right now.

Feeling pretty frustrated and useless at this point. With everything I’m tooled up to do on my 996, it’s pretty demoralizing to be so ineffective on a car that is mechanically simple by comparison.

Thanks everyone!

Van

[timothy_nd28]

I wouldn't worry about the manual, and don't be timid as there is a wealth of info on this site. The ECU is near and under the battery, the main harness connector unplugs pretty easy from the ECU. If you can locate the two pins in question, you'll be golden!

[Van B]

Money, thanks Tim!

[wonkipop]

Ok, lots of things for me to look at then lol. I’m new to the car and flying blind with no manual or other 914 guys around me.

Wonkipop,
Where is the decel valve? I’m doing this with no manual and I’ve only had the car two week so, hopefully you guys can give me some talk-ons?

Emery,
I don’t think I’m ready to mess with the distributor yet. I haven’t had a car with a cap in about 25yrs and I don’t have anything to retime the car. I do have a diaphragm on the distributor though so I’ll unplug and blow out all the lines. At least that will remove one variable.

Tim,
Uh you got anything to show me what the PIN numbers are? Otherwise, I think this might be outside my ability right now.

Feeling pretty frustrated and useless at this point. With everything I’m tooled up to do on my 996, it’s pretty demoralizing to be so ineffective on a car that is mechanically simple by comparison.

Thanks everyone!

Van

don't worry mate.
when i bought my 914 30 odd years ago i only had a haynes manual.
i didn't have a clue about L jetronic.
there were a few rare VW fastbacks that ran D Jetronic in Aus.
It was all a mystery. (still is).
i went from a twin carb vw squareback to the 914.

i sort of half get it but rely on my mechanic to really sort it when i get stumped.
particularly electronic test stuff.

timothy nd28 knows his stuff.

i'll dig up a pic of the decel valve and location.
i have mine disconnected.
i belong to the mob who thinks they are not so good.
it could be your problem but not saying it is.
you just got to go through things one thing at a time.

you can find the factory manuals on the net.
i can't remember where i found mine.
i downloaded them about 10 years ago.
the wonders of the internet. before that something like a factory manual was like finding gold at the end of the rainbow.
they are helpful. but won't necessarily solve your problems.
but its good for finding out what everyone is talking about.
decel valves, aar, etc etc.

[emerygt350]

Start simple. The retard brings the idle down to where it should be at idle and if it isn't working you get exactly that behavior. Get the idle to sit right by loading the engine. Then put it in neutral with emergency brake. Pull the vacuum line from the diaphragm and quickly plug the line with your thumb.

Idle goes to 1600?

Pulling the distributor is super easy, and you can mark the position of the cap and rotor before you pull it so no timing necessary.

[Dave_Darling]

I would start by checking the throttle valve. Blip it by hand. If the idle hangs up, grab the bellcrank (the arm that the throttle cable hooks to) and twist it in the direction the spring is trying to pull it. If the idle drops then, you have a sticking throttle. Cleaning may help, or rebushing might be needed.

Your ignition timing might also be sticking. Hook up a timing light and look at what happens to the blades on the fan when you rev up the motor and close the throttle. If the timing doesn't go back to where it started at idle, then there's a good chance something in the distributor needs help--either the vacuum unit, or the mechanical-advance weights inside the distributor.

Most air leaks will make the 1.8's L-Jetronic run lean, making for a really crappy idle, so those are lower down on the list of suspects. The exceptions are places where air can leak through a component that connects the intake boot upstream of the throttle body with the manifold downstream of the throttle body.

--DD

[Van B]

Hey everyone!
Working through the list of variables:
AFM looks healthy and happy. It has a clean reman sticker on it and the barn door is smooth with tension all they way through it’s range of travel.

Checking vacuum lines now. About to head to NAPA and get some bulk line for the ones that seem too hard or cracked at the connection point.

Throttle works fine, no hang. Snaps closed pretty aggressively.

Here’s a strange find; anyone know what this guy is or where he goes? Been unplugged a long time. It comes out of the right branch of the main loom.

[ClayPerrine]

Hey everyone!
Working through the list of variables:
AFM looks healthy and happy. It has a clean reman sticker on it and the barn door is smooth with tension all they way through it’s range of travel.

Checking vacuum lines now. About to head to NAPA and get some bulk line for the ones that seem too hard or cracked at the connection point.

Throttle works fine, no hang. Snaps closed pretty aggressively.

Here’s a strange find; anyone know what this guy is or where he goes? Been unplugged a long time. It comes out of the right branch of the main loom.

That is the wiring for the oil temp gauge. Gauge and sender were optional on 914s.

I would suggest you check the decel valve, the distributor advance, and make sure the plumbing is correct.

[emerygt350]

Yeah, we all have that. Apparently for a temp sensor none of us had or something like that.

[emerygt350]

Check the retard. It was made to bring the idle down. I don't believe your car has an advance. 1.8 might, 2.0s lost it in 74.

[wonkipop]

@Van B here is the decel valve and location.

[wonkipop]

here is a vacuum hose diagram for the 74 1.8