Idle Hunt - Followup to cold Start Valve Options

[ne14914]

OK here is the scenario -

When the car is cold - the idle is so low that you have to play "footsy" with the brake and accelerator to keep the car running.

After about 5 minutes the car will stay started - but idles up and down constantly -

What should I check, before taking it to a shop?

[TravisNeff]

AAR stuck closed - not too likely. Perhaps your cold start valve is gummed up is not able to shut off on it's own easily - try to disconnect the CSV power lead and try again. Check Brad Anders site for a cause and effect table on all your FI components. http://members.rennlist.com/pbanders

[ChrisReale]

What year is your car? Make sure all FI components are matched up.

[ne14914]

its a 72 1.7 FI.....

[boxstr]

Sounds like a vacumm leak. Air coming in and the brain thinks you need more fuel , up an down,etc. I would check for this with carb cleaner around common areas.
CCLinLOO

[mightyohm]

Try disconnecting the airbox temp sensor (TS1?) and see if it gets better or worse. On my 72 1.7 it makes a huge difference. For some reason the MPS I have wants to make my car run really lean. Still haven't figured that one out yet.

Maybe check your fuel pressure too.

These are just guesses. I'm troubleshooting similar issues.

[boxstr]

I have removed and diassembled a few MPS's and found that the diaphrgam has a hole. Cut a new rubber piece to fit and VOILA.
CCLinLOO

[Porsche Rescue]

I have same problem. Found it to be AAR (auxilliary air regulater). There is a vaccuum hose attached to the large rubber elbow coming out of the air cleaner (hose goes to AAR which then has a short hose connected to the intake manifold). Pull it out and cover with your thumb (while engine is running and "hunting"). If idle stabilizes, you have found the problem. Next check to see if the wire attached to the AAR has voltage. If it does, your AAR is bad. It is not closing as it should, thus allowing too much extra air into the manifold and confusing the ECU. AAR's are no longer available new. Not sure if you can clean/repair it. If not, only choice is to find a good used one.

[Porsche Rescue]

Just found a very helpful site thanks to DD on the Pelican Board: go to www.914fan.net/fuelpump.html
You will find a link to Kjell Nelin's D-jet guide. Among many other things, he describes a method for repairing the AAR. His guide may help with other issues as well. Easily understood info, even for a novice.

[jdogg]

What exactly is the function of the AAR valve and how does it go about its function?

[airsix]

What exactly is the function of the AAR valve and how does it go about its function?

The AAR valve is a "controlled vacuum leak" to increase engine idle speed. It does the same thing as opening the throttle a little (except the ECU sees the throttle as closed due to TPS remaining in idle possition). As spring heats up inside the AAR valve it closes the valve and shuts off the extra air to the intake. When it cools down it opens up again. The valve gets frozen up from years of crud and corossion. Both of my 914's came to me with stuck-open valves which means you get a 2,000rpm idle all the time. You can pry up the crimped lip on the top of the valve and pull the guts out to refurbish them. Just be careful not to break the (+) lead on the bottom of the can.

-Ben M.

[jdogg]

Thanks, Ben. What is involved with refurbishing? Just a good cleaning and lube or are there replacable/servicable parts in there? I too am searching down a hunting idle and suspect the AAR valve.

[ChrisReale]

one way to test the AAR is to let the car warm up fully and unplug the aar hose from the air box. If you still feel suction at full warm up then its stuck open. Spray some PB Blaster in there (not much) and let it soak and loosen the crud up :cursor:

Also, make sure your TPS is properly set.

[jdogg]

Thanks Chris - I'll try that before I open anything up.

[Brad Roberts]

Dont open them up. POP the top off of them after you "mark" the clocking position. The small tube on the top of the AAR comes off with a small amount of prying and twisting it. The steel sleave inside the top rotates with the bimetallic strip inside the base. You just need to free it up. It needs to rotate about 180 degrees. You can test them with a 12 volt source with the top off. You will feel it warm up and see the metal sleave move "around" in a circular motion closing off the atmospheric side and the intake side.

Very easy. Much easier than peeling the base back.

B

[Porsche Rescue]

Once more Brad, real slooooooooow. I think you're saying not to pry the AAR housing apart and that there is a better way. I understand what NOT to do but not sure what TO do.

[Brad Roberts]

I'm trying to locate a pic of this.

You know the small 90 degree tube hanging directly off the top ?? Pry it off. The piece that sticks and causes high idle is directly below this. It appears to be "staked" onto the AAR (the tube)


B

[Brad Roberts]

Here we go:

I use my famous paint markers and "mark" the clocking position so I can reassemble it correctly. Which only take a minute to tap this piece back on.

I should say this: test the damn thing first. DO not waste your time on a AAR that does not get HOT when you apply 12 volts. Test it with a small battery charger or some leads attached to a battery. I do these on a bench. Most of them I run across have the lead wire chafed where it enters the bottom. This causes your fuel pump fuse to pop if I recall correctly... not much fun.

B

[Brad Roberts]

Thanks PB:

The larger second arrow below points directly to the piece that sticks. use WD-40 to loosen it up. Your pointer finger should just fit down inside of it. Use your finger to start working it in a circular motion. You'll feel the bimetallic strip "tighten" up and release as you twist your finger in this hole. It need to rotate freely. Most of them stick.

B

[Porsche Rescue]

Thanks, I think I have it now. One more question, do I rotate back and forth, rather than 360 degrees, in other words, is the valve connected to the bi-metalic spring that I will "feel"?