idle is too high...1.8 AFC
 

My 1975 1.8 AFC is idling at about 1800 rpm. When it's cold it idles normal. But after it warms up a little it it won't drop below 1800 rpm. I try "blipping" the throttle, adjusting the idle screw on the throttle body. I've recently replaced all the vaccum hoses. I'm pretty sure I don't have a vaccum leak. But if I did, I would think the idle would stumble and die.

The car drives just fine. It's just annoying when I come to a stop sign or light and the engine is humming along at almost 2K.

Check the Auxiliary Air Regulator. It has vacc hoses that connect to the manifold, and to the big pipe between the air flow meter and the throttle body, There is one (possibly two-wire) electrical connection. Most of the 1.8 ones look a bit like cones lying on their sides.

The AAR should let air through it when it is cold, and should block all air when the engine is warm (~5-10 minutes of running). You can pull the hose off the large pipe, but be ready to block the opening in the pipe and the end of the hose. Removing the hose will create an enormous vacuum leak which may very well stop the motor.

--DD

I've checked the AAR with the two wires. The hoses appear ok and don't appear to leak...but I could be wrong. Would a vaccum leak here cause a high idle. On which side of the valve would a leak cause this. How do I check if the valve is operating correctly? And which way does air flow thru the valve?

Thanks,
Odie

Vacuum leaks on 1.8s (with the stock L-jet EFI) generally do not cause a high idle--they can cause a "hunting" idle (up and down), or juts plain crappy running. Most vacuum leaks in L-jet cars simply let in air that the FI doesn't know about, so no fuel is added to go with that air. This results in a lean mixture, which causes crappy running, and in some cases overheating and/or detonation.

The AAR can leak through itself. It is "fed" by air that has been measured by the airflow meter--air from that pipe that runs from the AFM to the throttle body. It in turn feeds the manifold. If it is stuck open, air that the FI does know about can go into the manifold, which will raise the idle.

To test it, pull the hose from the AAR to the intake pipe off the intake pipe. Plug the hole in the pipe and the end of the hose. When the engine is cold, air should be trying to go into the hose. When the engine is warm, air should not try to go into the hose.

--DD

Also check the decel valve... I'm not positive (and it's too cold to run to the garage), but I think the feed for that is T'd into the line that the AAV uses, and so a leak through that also uses measured air and will also cause a fast idle. Mine was leaking and caused it to run anywhere from 900 - 1400... now it's blocked off until I decide to replace or pitch it, and my idle is perfect.

I pulled the hose at the plastic "Y" plug in the intake bellows. There is a slight vaccum from the AAR with both cold and warn/hot engine. Not a strong vaccum but with my finger plugging the hose the vaccum builds slowly to a medium vaccum. I guess the valve is stuck open (or somewhere in between).

When you plugged the hose did the idle drop (should be 900 ideally)? You're better off pinching off the hose, as when you pull the hose to plug it, unmetered air will make its way back through the regular throttle valve, making the engine run lean. Pinch off the hoses and see which makes the idle drop, then you should have found your problem.

Plugging the hose and the "Y" fitting when I pulled it made no difference in the idle.

I've removed the Aux Air Regulator. It kinda can apart as I removed it. The end with the electrical plug slid out of the body. It appears to just be a strip of metal with some wire wound around it. A heating element I suppose. When I look into the cone end of the AAR, I can see some kinda mechanisim. But I can't see how it works.

Anyway, I plugged the holes on the intake manifold and the "Y" plug in the intake bellows. These are the two ports that the AAR connected to. And I still get no change in my idle problem.

I was browsing through the various parts for the FI system on some online catalogs. I came across the gasket that I believe is between the throtle body and intake manifold. There was mention that if this gasket is leaking, it can cause idle problems in the range of 1-2K...my problems started shortly, but not immediately after I had replaced every vaccum hose for the FI system and had removed the throttle body for cleaning.

how about the vacuum retard on the distributor? is it retarding the timing at idle or is it dead. is there vacuum in the hose to it at idle? pulloff the hose and see if the idle goes up.

as an owner of a 75 1.8 check the decel valve it is on the battery side of the engine bay.

mine was bad and my idle was 1800, i tried pluggin it but i would not do it again, because when you let off the gas but keep it in gear the motor draws a large vacumm on the intake side off the valves and can suck oil right through the seals ( ask me how i know ) and the motor can lean out a little ( from forced leaks )

just post a listing for it here somebody will have it, i paid 20 bucks

it is the same as one from a vw bus ( dont know year or engine ) it is the same part number and all

as to the aar put it back together but you will need to reach inside with a screw driver and hold the valve open when you put in the " metal strip with wire around it " with the metal strip vertical, and how it works is when the metal heats it flexs and the valve rotates closed when it cools it pushes the valve open

it is real clever too, the warmer the air temp the faster it closes ( warm motor mine closes in about 1 min ) but on really cold days it takes 10 min

Some great leads guys. I'll definitly make some headway now. It really could be any of those since it happened after replacing every vaccum hose so I probably upset or damaged something. The parts are 25 years old. I'm definitely gonna try to put that AAR back together thou and try saving a few $. Which way should that metal strip bend when inserting it? left or right?

Another 2 cents from 1.8L that has the same problem. Turned out to be the decel valve wasen't closing all the way. Pretty simple to test as mentioned in earlier posts.

Good luck!

as far as i know it either does not mater or the plug is keyed

when i put mine together it just when together with out much fuss and worked right

but the plug should have the metal loop on the top when hooked up