Idle Speed Issue - 1975 1.8L Options

[telank]

I'm in need of ideas to resolve an idle speed dilemma. My 914 is a 1975 1.8L which I bought about a year ago. It seems to be very stock and still has the L Jetronic FI system in place. Here is the challenge.... I have been using the process in the Haynes manual for setting idle speed. If I set the speed when the car is warm, the next time t is started cold it is difficult to start and will idle so slow it barely stays running. Once warmed up all is good. If I set the idle speed right after starting before it is up to temperature - after it does warm up - it will be idling at over 2,000 RPM. Outside of this issue the car runs good and strong. The plugs are perfect color - so no indication of too lean or rich mixture. Thanks for your thoughts or ideas!

[Sleepin]

More than likely a vacuum leak. Set it per the manual and then try to track down any brittle or cracked vacuum lines. The L-Jet is very vacuum dependent. You could also check the fuel cap gasket IIRC, a bad gasket can cause idle issues as well. That's just my $0.02...I may be mistaken.

[AZ914]

What Sleepin said.. Does the L-Jet system have an AAR or cold start valve? I'd start there.

[timothy_nd28]

Aux Air Valve most likely stuck

[telank]

I have replaced all the vacuum lines so they should be OK. When you say the auxiliary air valve may be "stuck" - can they be "unstuck" by cleaning or some other repair? Or do I need to just replace it?

[Dave_Darling]

The early L-jet cars had the same type of AAR as the D-jet cars did. It has a rotary valve operated by a bi-metallic coil spring that rotates as the heating element in the bottom of the can warms up. (Or as the whole thing is warmed by engine heat.)

The later L-jet cars had a disk valve rotated by a bi-metallic lever which curled/tilted when it heated up.

Either one has a rotating piece, a bi-metallic temperature-sensitive piece, and a heating element. The rotating piece can be cleaned up with solvent or a good penetrating oil, and the heating element can be checked with an ohmmeter. (Should read about 10-30 ohms between the connector and the housing or between the two pins in the connector if there are two pins.)

If the cleaning fails, they can be CAREFULLY opened up and more aggressive cleaning done.

--DD

[pete000]

Like Dave said, the AAR is not working properly. Check to see if it is functioning. Also check to verify it is getting power when the car is running. I have an issue of mine not getting power causing the AAR not to work.

Yours sounds like it might be stuck closed or not getting power.

Take it out and soak it in Kerosene for a few days, blow it out and hook it up to 12V and see if it opens. If it does check it in the car to see if it is getting power and opening.

Lots of posts on how to do this.

One more thing it to not have any vacuum leaks ! The L-Jet is very sensitive to any air leaks. Poor and erratic idle is almost always an air leak problem.

[telank]

Last evening I removed the AAR to investigate the problem further. When I went to disconnect the wiring harness the heater element pulled right out of the housing of the AAR! A pic is attached. I applied 12v to the heater connector pins and the heating element started to warm. I didn't have time to watch long enough to ensure the bimetallic strip moved, but warmth seemed like a good start! I also was able to loosen up the internals using WD40. The internal "valve" mechanism appears to be spring loaded. So I assume when I put this back together I need to position the bimetallic strip so that it pushes against the spring loading and the valve is open when cold and as it heats and moves the spring pressure will close off the air passageway? Am I thinking correctly? Also, is there any reason why epoxy would not be a good choice to glue the heating element assembly back into the housing?

[Dave_Darling]

You appear to have the disc-valve type of AAR.

Your plan seems reasonable.

--DD

[telank]

Dave,

It definitely is a disc style. Thanks for the quick feedback!

Tim

[TheCabinetmaker]

Will this type of valve provide more, or less air volume?

[telank]

Will this type of valve provide more, or less air volume?

What I think I've learned through the process of sorting this problem is......

At least a couple versions of these auxiliary air valves were used on 914's through the years. All valves were open when cold to provide extra air into the engine during warm-up. As the engine warmed the valve closes. If the valve is working properly the bimetallic coil or strip inside the valve is heated by a heating element and that closes the valve.

If the valve is not functioning properly for some reason, or stuck open or closed you are not getting the proper amount of air. The problem may be most noticeable at start up or when warm - depending on how one has adjusted the idle speed screw.

In my situation the valve was stuck closed so the engine would barely idle and run when cold. Once warmed up all was good and the engine idled smoothly. If I adjusted the idle screw so that it idled properly at cold start up the idle speed would rise to ~ 2,000 RPM when warm because I had opened the throttle excessively to allow the engine to idle when cold to compensate for the non-functioning AAR.

There are folks who know much more about this than do I. So if I've misstated something hopefully they will jump in and correct any confusion I may have created!

[TheCabinetmaker]

I'm aware of the operation, and your assement is correct. My question was about amount of airflow between the two. (IMG:style_emoticons/default/huh.gif)

[telank]

I'm aware of the operation, and your assement is correct. My question was about amount of airflow between the two. (IMG:style_emoticons/default/huh.gif)

OK, sorry for the long-winded explanation, but good to know I am on-track (IMG:style_emoticons/default/smile.gif)

I haven't seen the other valves first hand, but the valve on my car has a bore diameter of ~ .375" to .5" when fully open. How long it stays open would seem to be another major factor in how much airflow it allows.

I hope to get mine reassembled within the next couple days and will test its operation before reinstalling it on the car. I can post how long it takes for the valve to close if you or others are interested?

[TheCabinetmaker]

Hmm, I think I'm being baited

[telank]

Hmm, I think I'm being baited

Baited? (IMG:style_emoticons/default/huh.gif) No, just offering to post what I might learn if there is interest. (IMG:style_emoticons/default/type.gif)

[Dave_Darling]

One thing that can be done to estimate the amount of flow through the two valves would be to measure the opening of the valve when it is all the way open. If you have the disc-style one apart, you can just measure the opening in the disc or trace it on paper or some such. Measuring the rotary one would be a bit more difficult, but if someone has it completely apart they should be able to measure the hole.

I don't know how the openings in the valves compare. My guess is they are at least somewhat similar, because some early 74 1.8s used the rotary valve style AAR, like the D-jet cars did. But that is just a guess.

--DD

[TheCabinetmaker]

Dave, I've determined that the stock rotary aar does not supply enough air for my cammed 9:1 compression 2056. Looking for an alternative aar that would supply more air, or even be adjustable. It just won't idle cold. I can remove the hose from the aar outlet and make it idle properly by letting a little more air in.

[Porschef]

Pardon the hijack; Curt, what cam are you using? I'd love to get to the bottom of my cold start issue, i.e. stalling and or slow/rough running for the first thirty-sixty seconds, depending on ambient temp... (IMG:style_emoticons/default/dry.gif)

2056, 9550 cam, L-jet

[TheCabinetmaker]

Same as yours and same symptoms. It runs, but very low rpm.