75 914 2.0 Idle problems

[PMatos]

Hi Everyone,
I have a 1975 914-4 2.0 (euro spec) that was parked in the garage for about ten years or so...last year we rebuilt the fuel injection system and got the car running. The engine pulls smoothly and feels pretty healthy to me but, after the car gets warmed up, it idles too high (between 1800 and 2100 rpm). I have already replaced the ECU and the air temperature sensor, but the car still idles crazy. It only starts doing this after the engine gets properly warmed up, while it's cold it idles perfectly (900-1000 rpm). Any help will be appreciated!

[Dave at Pelican Parts]

There's a vacuum leak somewhere. Either that, or the timing is overly advanced.

There may be other things messed up that compensate for the above when the engine is cold, but your basic problem sounds like a vacuum leak.

--DD

[PMatos]

Thanks, I will check for leaks as soon as possible

[Tobra]

There is a diagram around here with correct vacuum hose routing too

http://www.pelicanparts.com/914/technical_specs/914_20FI_diag.htm

[John Rogers]

Once the engine gets hot, do the carb cleaner spray all around trick. I am guessing it is the intake tubes to head gasket that are loosening on heat up, but I am an old guy and my memory is fading...........

[TheCabinetmaker]

you motor should have a device to allow extra air into the intake, bypassing the throotle body. this is done via an auxilary air valve, located near the oil filler. this is a small can, with two hoses on top for the air, one wire (for an internal heater). the can is about 2 inches tall and 1.5 inch diameter.

As the valve warms up (either via the interanal heater or by a hot engine bay) the valve closes off this extra air supply.

If the valve is stuck open for any reason, then you will likely find when cold the egine idles fine, but once she warms up, and you still getting that extra air via a stuck valve, you will find you have fast idle.

this device is there to give a fast idle when cold, so give that valve a check. once the motor is fully warm, pull off the hoses and block them, if the idle speeds drops back to normal, then you found the issue. It is faulty valve.

other than that you may have leaks elsewhere too.
But give teh air valve a try, the test is quick and easy.


there are write ups on the web on repair of this valve. usually involving soaking the valve in penatrating oil to loosen up a stuck one that may have gotten rusty. The internal heater may also not be working, bad wire, burned out heater, no power to it etc...

You can pull the valve apart by prying up the metal. (try soaking first if it is stuck, the prying process is messy, pry open the valve as a last resort)

you should be able to gently blow air thru the valve when cold, and not so when warm, that is another way to test it.

[rory gallagher]

Originally Posted by TheCabinetmaker

you motor should have a device to allow extra air into the intake, bypassing the throotle body. this is done via an auxilary air valve, located near the oil filler. this is a small can, with two hoses on top for the air, one wire (for an internal heater). the can is about 2 inches tall and 1.5 inch diameter.

As the valve warms up (either via the interanal heater or by a hot engine bay) the valve closes off this extra air supply.

If the valve is stuck open for any reason, then you will likely find when cold the egine idles fine, but once she warms up, and you still getting that extra air via a stuck valve, you will find you have fast idle.

this device is there to give a fast idle when cold, so give that valve a check. once the motor is fully warm, pull off the hoses and block them, if the idle speeds drops back to normal, then you found the issue. It is faulty valve.

other than that you may have leaks elsewhere too.
But give teh air valve a try, the test is quick and easy.


there are write ups on the web on repair of this valve. usually involving soaking the valve in penatrating oil to loosen up a stuck one that may have gotten rusty. The internal heater may also not be working, bad wire, burned out heater, no power to it etc...

You can pull the valve apart by prying up the metal. (try soaking first if it is stuck, the prying process is messy, pry open the valve as a last resort)

you should be able to gently blow air thru the valve when cold, and not so when warm, that is another way to test it.

Should the AAR close fully (airtight ?) when at operating temp ?
Does it respond to both 12V and ambient temp ?

[TheCabinetmaker]

Yes it should be pretty much air tight when closed, you should not be able to blow any noticable amount of air thru it with your lungs.

the valve has a bimetallic spring in it that closes the valve when heated. the electric heater element is some what of a timer, it takes a given time to close it. in a cold ambeint (say freezing snow conditions) the heater will take longer to close than on a 100F day, but that is ok, as in cold weather you need the extra air this valve supplies for a longer time period.
If the engine is already warm (say after a long drive) even though it may be a cold day the bimetallic spring inside is already pre-heated by the heat of the engine to which the valve is bolted to, so the valve will close faster than if the engine was sitting off for a long time, that too is ok as a pre-warmed up motor does not require so much extra air.

if it is a hot day and the engine is very warm already from driving, the valve will already be partially closed, and the heater will finish closing it very fast if it is not closed already. on a cold day on a warm engine, the heater will take more time to close, than on the warm day with a warm engine

you should be able to feel the valve get warm (assuming it was fully open, already cold, before testing ) by leaving the power on it for a while, if it dont heat up, then suspect the heater is not working, in which case test for power to the heater, if that is good, ohm out the heater, it could be shorted or open, either would cause it to not work (often the heater fails cause the wire to it is shorted to ground at the crimp at the valve's base (causing a fuse to blow) or the wire broke near the crimp. it is rare to actually have the heater element burn out.

the other failure is the inside is gummed up, got wet and rusted, or otherwise sticks so that dispite heating the valve cant rotate shut, a soak in solvent and WD -40 can sometimes unstick them without having to open them up. opening them up is a pain as you got to pry up the rolled over top flange, then it is a pain to seal back up at least if you want it to look good.

so a cold valve should be easy to blow air thru with your lungs, and a fully heated valve should be near impossible to blow air thru with your lungs.

also be sure that the hoses are corectly hooked up, else the system may not work correctly, the inlet hose must take air before the throttle body, the outlet must return air after the throotle body. the inlet air should be taken after the aircleaner, not before, else unfiltered air will enter the engine.

[PMatos]

Hi everyone,
I used WD-40 in the AAR of my car and left it settling overnight. This morning I took the car for a drive to warm it up properly and, after the needle in the temperature gauge reached middle ( with the engine idling at 1600 rpm), I disconnected the lower hose of the AAR, this caused an immediate rise of the idle speed to 4000 rpm. I blocked the hose with my finger and the idle speed dropped to 1600 rpm. I think my AAR is working properly, otherwise the idle speed would have dropped to 900 rpm when I blocked the hose.
So there is something else causing my engine to idle fast after warming up... I will check for air leaks but, other than that, I can't think of any other problem that causes a fast idle speed.

[seventythree]

I don't know about lower vs. upper, it's been too long.
Disconnect the hose coming from the air filter housing. It shouldn't, and most likely won't, make any difference in your idle speed. Once the AAR is warmed up, there should be no air being sucked in. If you put your thumb over the hose to block the air flow and the idle drops, you have a leaky AAR. Replace or repair.