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

did your mechanic tell you where the boot was leaking?

there are four connection points.

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

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

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.....

sorry. thought you meant you had replaced it and it was still leaking.


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.

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.

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.

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

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!

Click to view attachment

Money, thanks Tim!

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.

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.

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

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.

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

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.

@Van B here is the decel valve and location.

Click to view attachment

here is a vacuum hose diagram for the 74 1.8

Click to view attachment

Wonkipop, thanks! I’ve been going back and forth referencing the other thread:
http://www.914world.com/bbs2/index.php?sho...;hl=Decel+valve

So, I replaced both vacuum lines from the distributor diaphragm to the throttle body. I used some close but not quite right tube they had at NAPA… for my NARP lol.. sorry couldn’t resist.

Anyway car felt a little better on acceleration so I know those lines were too old and hard. But, I still got the 1600rpm idle once the car was warm and only when I was slowing down from driving. In the garage it idled like it should even after bringing revs to 3k, holding, then letting go.
While I was driving I even tried clutching at speed and the revs still didn’t fall to idle.
Unplugged line 7 per your updated diagram and the car stalled so, does that mean decel valve is working?

you ought to unplug line 7 and 8 from the decel valve and then block the lines with a plug, use something like a bolt that fits snugly to plug the lines.

that should mean the action of the decel valve does not come into play.

for good measure unplug the small line 9 and plug.
then its really out of the circuit.

----

as a separate test you can simply pinch the line from the aav.
with the decel all hooked up.
line 6.

there is more to testing the decel valve.
i'd have to re read the factory manual.
get back to you on that.

You say you replaced the hoses, did you verify they were going to the right places? It really matters.

What am I looking for when I do that?

Also, I just had another thought; when cold starting these cars, should it high idle for warm up? Mine definitely does not. When cold starting it lopes along trying to hold a normal idle?

Yeah, they’re in the right orientation. The last thread were you guys posted the diagram was helpful. My car is a 12/73 build date, but it has the two lines without EGR.

yours should be the same as mine. mine is a jan 74.


as to factory manual testing decel valve.
its really a basic test to see if its working or not working and nothing inbetween.
you can pull just the hose where it goes into air cleaner boot.
rev the engine to mid range (reach down and twist the throttle).
then snap the throttle off.
you should feel some suction through the hose.

i'm not exactly sure how a sticking decel valve hangs the revs coming down to idle, others can explain better and it may not be your problem.
but if you can take it right out of the circuit as i suggested by disconnecting all hoses and plugging them for one test and see if your idle doesn't keep hanging it might be the problem. in any case you will have tested and eliminated.

Kinda. The aux air system handles that but it is a real fudge of a way to do it.

I put a valve on mine so I can block it quick while troubleshooting.

The retard needs to go to vacuum below the butterfly in the throttle body. That port should pull strong vacuum at idle. The advance port should have no vacuum at idle. If you have plugged your advance into any old port it will advance your idle and do nothing to advance your ignition when it needs it.

Ok, this might be something. See the difference in configuration? These lines are all real old so, it’s been that way a long time.
http://www.914world.com/bbs2/uploads/post-...-1635717303.jpg

Again, notice the diagram, that dotted line leasing to the diaphragm on the distributor is because they left the advance disconnected post 73.

Line 7 is the same, but 8, 9, 10, 11 are exactly the opposite.

Yeah, the t is real. That should be there. That is plenum vacuum. One should go to the decel. The other can go to the retard if needed but God I swear I have recently read about it going somewhere else.

According to the diagram it goes to the fuel pressure regulator... Hmm.

Say what now?

I have seen several revisions of that diagram in the past three weeks too, so there maybe some variation. Best to just go by what kind of vacuum it needs and checking to see if it is getting it.

Yeah seriously. They just left it dangling.

Your's is the one with the finger point? Is the white sheath in the throttle cable supposed to stick out that far?

I have heard of the port being plugged on the tbi, the hose just laying on the motor.

looking at your photos the decel valve is correctly hooked up.

as to the business with the distributor retard lines.
mine is the same as the diagram.
i have two ports on the throttle body.

some cars have only one retard line to one throttle body port.
the other port is blocked and the other line from the distributor is an open hose that is just tucked under distributor.

don't worry about it. its some kind of emissions tweak again.
i suspect the 74s built in calendar year have the open hose.
after that it goes to a two port throttle body.
i did have this explained to me by my mechanic about a year ago and have forgotten it.
its probably something like vw getting ready for 74 calendar year emissions regs with the set up for L jet but not doing the final tweak until they had to.
my mechanic explained to me what the second line hooked up to the second throttle port would do. but again don't worry.

your decel lines are correct from the photo.

The T on the green line does go to the fuel pressure regulator. Took me a minute to trace it because it disappears in the bowels of the engine bay, but I was able to confirm by pulling on it.

I have both lines from the distributor diaphragm going to the throttle body just like wonkipop shows. All the dashed lines are actual lines on my car.

I think we’re at the end of the road on vacuum lines. Everything is as it should be.

i see what the problem is with the diagram.
its badly drawn schematic/representation of the decel valve itself.

your photo is correct.

That’s me, and probably not. But the throttle works so, I’m not gonna mess with it.

@Van B

rhodyguy is on to something.

Verify that you are not getting vacuum to the advance at idle and you are getting vacuum to the retard at idle. Also, figure out which side is advance and retard. If I remember right, the outer part is the advance, the inner is the retard..

Ok so, Recap for a problem still not solved:

-Vacuum lines are GTG
-AFM healthy
-TB ops normal

Symptoms:
-No high idle on cold start
-high idle when driving but not in the garage
-normal engine ops in all other aspects

Not yet checked:
-decel valve
-continuity between pin 2 and 18
-confirm vacuum at TB

Copy. I’m outta time for this week. I’ll be away from home all week so, better luck next weekend I guess.

How so? Throttle works fine. Full range, smooth, and it’s even shiny.

You will get it figured out.

Oh I’ll still be leaning on you guys pretty hard.

I have only been working on mine for 6 months but this forum is fantastic. I have 35 years of other car experience, so that helps (just be happy you are not working on a Ford CFI HO 302), but the people on this forum are really great and super helpful.

I like the progress and sounds like you are headed in the right direction. Consider ditching the decel valve all together, I threw mine out many years ago. The decel valve feathers the RPM back down slowly, as if you were driving some Toyota Camry. Without the decel valve, gives a more spirited type of feel, like driving a Porsche.

I'm not sure if I'm the only one that had this issue, but these reproduction intake boots were not the exact copy of the OEM. The fittings that plugged into the boot were very loose and very lossy with vacuum leaks. I ended up machining some new fittings that fit the reproduction boot much much much tighter. Since I'm not using a decel valve and I don't have a EGR, I made a plug for one of the openings. It was the first time I ever used a metal lathe, and happy that I didn't injured using the machine
Click to view attachment

It may be worth spraying some starting fluid on the intake boot fittings while the engine is running to see if anything changes, or do a smoke test again. I don't think this is your current problem, but is worth double checking.

Hey Tim,
Yeah I saw the thread where you posted about your fancy fittings. I like em! I had the OE large fitting and just put some gasket maker on it before pressing it in the new boot. You are right though, the reproduction pieces are a little too short in length and the ports are a little too loose.

For my car, 1974 1.8L, the upper port is smaller. So, I was able to find a plastic fitting that seals up. The one that was on the car was for a 1975 1.8. It was so old and beat up… sealed with brass threaded fittings and plumbers putty! I mean probably two previous owners drove this car in a poor state of tune for decades!!!

I went the other way and found a new old stock decel valve on eBay. I’m pretty pumped about that actually. It should be here when I get back home later this week. My aim for this car is to make it feel like it did when it was brand new in 1974. I have another Porsche that is heavily modified for when I want to go fast.

Random thought for everyone still helping me solve this riddle:
Even though the throttle body works smooth, could the TPS be causing a problem? Or, would a bad TPS manifest with other symptoms like hesitation and stumbling?