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

[wonkipop]

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

@Van B

rhodyguy is on to something.

[emerygt350]

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..

[Van B]

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

[Van B]

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..

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

[Van B]

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

@Van B

rhodyguy is on to something.

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

[emerygt350]

You will get it figured out.

[Van B]

You will get it figured out.

Oh I’ll still be leaning on you guys pretty hard. (IMG:style_emoticons/default/beerchug.gif)

[emerygt350]

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.

[timothy_nd28]

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


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.

[Van B]

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?

[timothy_nd28]

The TPS (not sure if it is truly a TPS) has two microswitches. It tells the ECU that you are at idle via pins 2 and 18. The TPS can also tell the ECU when you are at wide open throttle at pins 3 and 18 thru the second micro switch. The ECU receives no other info when the throttle is in between idle and wot.
When at idle, one of the TPS switches will electrically close and command the ECU to drop in RPM. This part almost never fails, but these cars are getting up in age, anything is possible, especially intermittent problems.

A bad TPS will cause a high idle, but I don't think it will effect much of anything else. It's worth testing to rule this variable out.

[emerygt350]

TPS isn't going to do the throttle hang. It's worth thinking about, but not for this issue. Try unplugging it...

[emerygt350]

Again though... You have all kinds of non intrusive troubleshooting before you start mucking with the TPS...

[wonkipop]

@Van B - L jets forever. (IMG:style_emoticons/default/beerchug.gif)

i wish i had another 74 1.8 sitting around to hot rod like timothy nd28.
sounds like the gear.

you will crack your problem.
stick to the methodical attack of one thing at a time.

[Geezer914]

I have a 75 1.8L from CA. I live in NJ. The first thing I did is get rid of all the pollution crap. Not running the decell valve. Only vacuum line is to the distributor. Do another smoke test. The crack in the boot took the pressure out of the system. You can make a smoke tester for under $20, look on you tube. L jets hate vacuum leaks. Could be injector seals?

[StarBear]

When it happens on my 1.8, a drop of light household oil on the felt pad below the dizzy rotor usually works. Otherwise, a vacuum leak somewhere.

[emerygt350]

I know the decel helps the longevity of the MPS on djet. If it isn't protecting something on an ljet, I would get rid of it too.

[Van B]

Riddle me this Batmen:
Why would clamping just that line stop the high idle??
Keep in mind #7 and #9 should be reversed on the diagram.

I replaced the decel valve and nothing changed. But when I clamp that line, idle will drop to 1200rpm immediately after releasing the throttle and then slowly down to idle.

[emerygt350]

But what is clamped? Where is it coming from and where is it going on your motor?

[wonkipop]

ok mate.

i think clamping that line is telling you its something else that is responsible for hanging up the idle or its a combination of things and you still have to find it.

i've looked at your photo, the decel is plumbed in correct.

clamping test you have done in photo reliably takes decel out of the circuit.
if the decel valve was the problem it would drop to proper low idle straight away.
but it wants to drop fast with the decel valve out as you would expect.
something else stops it a 1200 - not the decel valve.

my conclusion would be the decel valve is good.

your original decel valve was likely fine too.
having it in the circuit exaggerates or masks what is really causing the problem.

have you done the other things suggested by other members.

for instance lubricating the distributor.

keep doing one thing at a time.