How do you adjust idle on 1975 1.8L l-jetronic Options

[steveneashcraft]

Assuming that everything is right. Where is the idle adjustment on a 1975 Porsche 914 with a 1.8L engine with l-jetronic. Car is absolutely stock.

[Cap'n Krusty]

Assuming that everything is right. Where is the idle adjustment on a 1975 Porsche 914 with a 1.8L engine with l-jetronic. Car is absolutely stock.

The big fat screw on the throttle body. Before you touch it, do the dwell and timing per the established L-jet procedure. The Cap'n

[steveneashcraft]

Assuming that everything is right. Where is the idle adjustment on a 1975 Porsche 914 with a 1.8L engine with l-jetronic. Car is absolutely stock.

The big fat screw on the throttle body. Before you touch it, do the dwell and timing per the established L-jet procedure. The Cap'n

Thanks. That's what I thought but I pulled it completely out and there is nothing under it. I expected to find a needle valve and spring. Dwell and timing are correct (had to use a friend to hold a constant idle while checking). The big fat screw has very fine threads which is what I expect. When I look down into the hole when the screw is out there is what appears to be a rod across the bottom of the hole but nothing else. I just bought the car so it's possible that someone else was "fixing" the idle and left something out. Ideas?

[Bleyseng]

its a air bypass screw nothing to it really

[Cevan]

That rod is the top of the butterfly valve. I just checked my 1.8 throttlebody that's sitting in my cellar and there is only the large screw, nothing underneath it.

[steveneashcraft]

Thanks for the quick reply. I'm still confused about how to set the idle on a 1.8 L-Jetronic. If that screw allowed more air to bypass the butterfly valve or moved the butterfly valve then I'd understand how it could adjust the idle. Does it do either or is it just a plug on the 1.8L throttle body with L-Jetronic since the same throttle body is probably used on other 914 intake systems? Ideas?

[Cap'n Krusty]

The "hold the idle steady" comment scares me. Here we go, brief version. To set the timing, remove AND PLUG the 2 vacuum lines at the distributor. The idle speed should rise substantially. Don't have any? Stop right here and get the right distributor. Turn the air bleed screw in until the idle is at 800 RPM. Remove the cover of the timing mark observation hole and shine the timing light in there. Look for the mark, which is red. If you don't see it aligned with the "V", make it do so. If the car runs at all well, it's gonna be close enough that only a minor adjustment should be necessary. Tighten the 10mm locking nut on the distributor clamp, and recheck the timing again. Readjust as necessary (clamping it down frequently moves the distributor slightly). Unplug and reattach the hoses, and turn the air bleed screw OUT (CCW) until the idle speed is again at 800 (or 850) RPM. You're done. If you used ANY other method to adjust the timing on your L-jet equipped engine, you did it wrong.

Have a nice day .............. The Cap'n

[steveneashcraft]

The "hold the idle steady" comment scares me. Here we go, brief version. To set the timing, remove AND PLUG the 2 vacuum lines at the distributor. The idle speed should rise substantially. Don't have any? Stop right here and get the right distributor. Turn the air bleed screw in until the idle is at 800 RPM. Remove the cover of the timing mark observation hole and shine the timing light in there. Look for the mark, which is red. If you don't see it aligned with the "V", make it do so. If the car runs at all well, it's gonna be close enough that only a minor adjustment should be necessary. Tighten the 10mm locking nut on the distributor clamp, and recheck the timing again. Readjust as necessary (clamping it down frequently moves the distributor slightly). Unplug and reattach the hoses, and turn the air bleed screw OUT (CCW) until the idle speed is again at 800 (or 850) RPM. You're done. If you used ANY other method to adjust the timing on your L-jet equipped engine, you did it wrong.

Have a nice day .............. The Cap'n

I usually don't respond to comments that don't have anything to do with my post but I can't resist. I need to know how to set the idle on a 1.8L L-Jetronic. I know how to set and check the timing. I can't get the car to idle without having someone or something pull on the throttle cable. (i.e. someone hold the idle above the rpms needed to not stall). It seems like the easiest way to do this is to have someone sit in the car and watch the tach, listen to the engine, and hold a steady 900 rpm. Vacuum lines were set up to check the timing. It was correct.

If you know a better way to check the timing on a car that runs fine but dies from a low idle condtion please let me know.
If you don't give it any throttle after the car starts the car stalls. I know I could check the static timing but since at a constant 900 rpm the timing is spot on I don't think I need to.

Car starts when it is cold. Car starts when it is warm. It just doesn't idle.

The mystery is still "HOW DO YOU SET THE IDLE ON A PORSCHE 914 1.8L (1975 California car).
If the car won't idle and when you pull the 'The big fat screw on the throttle body' and can see the top of the butterfly valve what should you do next. Since 'The big fat screw on the throttle body' on my 1.8 doesn't have anything that I can see to adjust the idle I need some advice from someone who knows if there should be something under the 'The big fat screw on the throttle body'. At least one very helpful forum contributor checked his 1.8L throttle body in his basement and said there was nothing under the screw except a view of the top of the butterfly valve. I thought it was a rod but after checking my throttle body I have determined the helpful forum contributor was right. Thanks for some useful info.

So a few questions:
1) What should be under the air bypass screw on throttle body on a 1.8L L-Jectronic? On a 2.0L D-Jetronic there is a needle valve, spring, and needle seat under this screw.
2) If the answer to 1 is "nothing but a view of the top of the butterfly valve" then how do you adjust the idle?


Sorry this is so long but I'm a newbie to this forum and hope to find someone who can answer my question about how to adjust the idle on my car assuming that everything is correct except for the idle. Even if the timing on my 914 was wrong it would be great if I could just get an answer to "How do you adjust the idle".

Hope I haven't offended anyone. Thanks and have a nice day.

[Dave_Darling]

1) What should be under the air bypass screw on throttle body on a 1.8L L-Jectronic? On a 2.0L D-Jetronic there is a needle valve, spring, and needle seat under this screw.

There is no needle valve under the screw on a 2.0 throttle body. The screw itself is a valve; the end of the screw blocks a hole that goes through the throttle body from "upstream" of the throttle plate to "downstream". This hole bleeds air through it; the amount depends on how far in the screw is or how far out it is backed.

The 1.8 air bleed screw is the same way. The end of the screw plugs a hole that is going through the throttle body. Screw it in all the way and very little air goes through. Unscrew it and more air goes through, raising the idle.

--DD

[steveneashcraft]

Dave,
Thanks. That makes sense. I was told that there was a needle valve, etc. on the 2.0L D-Jetronic and I believed it. I think my problem at this point must be a huge air leak so that the idle adjust doesn't have any effect. If the idle was high I'd really believe big leak but my problem is that the car won't idle at all. Start fines (cold or hot). Runs fine but when the throttle is released and it gets to 800 rpm it just keeps going to 0 rpm. Ideas.
Thanks again,
Steve

[Cap'n Krusty]

OK. If you can't get it right with the air bleed screw, it's REALLY likely you have a vacuum leak. Unlike most induction systems where a vacuum leak will make the engine run faster, a vacuum leak on an L-jet car will make it not idle at all. Pull the oil filler cap and make sure BOTH gaskets, the flat one AND the o-ring, are there and in good condition, and that the cap is screwed on straight and tight. If fixing that doesn't do it, check all the vacuum lines, look for any place where a hose might go but doesn't, check the intake boots (hoses) and the nuts holding the manifolds to the heads, and finally, the valve cover gaskets. BTW, how did you set the timing if you couldn't make it idle? Holding the throttle steady isn't the best way to get it right, and it's 800, not 900RPM.

Besides all that, the valves need to be set at .006" or looser, and they need to all be pretty much the same setting. I say "or looser" because the car will actually run cleaner at .012-.016, something we "could" do for smog testing purposes where appropriate. Of course we wouldn't really do that, 'cause it would be illegal.

As to the appropriateness of my post, you CANNOT set the idle with the timing off, so setting the timing is the first step. You can't set the timing with the idle off, either. The car obviously doesn't run fine except for it dies at idle, because the idle is a critical part of running fine.

In closing, I think you may have misinterpreted my answer as being irrelelvant. For that, I'm sorry. However, I supposed you knew what an air bleed screw is, and it appears your idea of an air bleed screw was more in the line of that they use on many (but not all) carburetors. Go back and look at the things I've outlined, and get back to us. The Cap'n

[ndfrigi]

Hi Steve,

I'm also a newbie with 914 (1975 1.8L), I got mine last Aug. 2011. Anyway, I agree with Capt and other members of their comments and suggestions.
Just to give you also my side, my teen was not running since 2003 from previous owner (my neighbor around the block), so that is 8 years non running teen. What I did first is to replaced battery, replaced all vacuum lines, replaced all fuel lines (except fuel lines along the tunnel), drain gas tank and after that, the car already running but the idle only good for 1,200 rpm and if I lower it, it will die. Until now, I did not touch my distributor cap or adjust anything with it. So after driving the car for a while, I tried to look for some more issues to lower my idle below 1,000. So yes I did find one thick rubber hose attached to the intake manifold just beside the cold start valve that was kind of loose, so I replaced that and now the idle stays below 1,000 and does not die anymore and it start better even in the morning. Still planning to check or adjust the valve which I assume needs to be adjusted. In regards to the idle screw, I had a hard time adjusting the idle with that screw until all the vacuum lines are perfect.

Thank you and God Bless!

Noel

[TheCabinetmaker]

Wow, whered ya find that old thread. I hope he has it figured out by now. I wonder how come we never heard back from him?

[76-914]

So there was a time that (IMG:style_emoticons/default/poke.gif) the Cap'n was a sweety.

[Cap'n Krusty]

So there was a time that (IMG:style_emoticons/default/poke.gif) the Cap'n was a sweety.

Either I was drunk or there was an imposter there trying to ruin my reputation ............

The Cap'n

[TheCabinetmaker]

(IMG:style_emoticons/default/lol-2.gif)

[messix]

i had this problem once and it was vacuum leaks on many hoses. replace them or trim them back a little of the hard crusty ends.

[double-a]

I recently performed some troubleshooting on my '75 1.8 and I thought I'd record my experience here for posterity! For months I've had to deal with dodgy idle, dying when rolling to a stop, random power surges at speed, and more. I replaced the AAR, which helped some, but didn't solve the problem.

The issues seemed completely random. Sometimes it would drop to idle perfectly, other times not. Sometimes there was plenty of power (for a 1.8), other times it was all over the place. Ran rich, with terrible gas mileage of course.

Timing was set correctly, vacuum lines were all checked and trimmed, then checked again. So what was it?

For my problem, the solution was ridiculously easy: a sticky AFM flap. Years of dirt, oil particles and other crap had accumulated on the smooth inner surfaces of the AFM, causing the flapper to stick at random times. An hour of my time and a cup of solvent was all it took to make the car fabulously fun to drive again.

So... like the others have said, check the most obvious stuff: timing, vacuum lines, etc., but also some that are less obvious.

[Geezer914]

Having the Cap'n reply to posts is worth the price of admission! (IMG:style_emoticons/default/lol-2.gif)