high idle in neutral only

[jchandler01]

Excuse me. Baby Boomer who knows not how to converse in a forum, or any tech fashion. Getting desperate as young mechanics have never seen a carbureted vehicle. Love my first new car, 85 FWD/4WD GL wagon 1.8. Cannot get to pass smog with high idle in neutral. New Cat Converter and replaced a broken vacuum hose. Could not even remove air cleaner as it is stuck on. Is on 3rd carburetor and last mechanic to work on it said idle set as low as possible. I've moved and he may have passed away by now.  Smog inspector suggested vacuum problem but cannot really converse due to rules. Read about a possible Intake Manifold Gasket leak.Idles and runs smooth all the time and gas mileage not changed. Have yet to find someone here who knows carbs and it may be unrelated? Idle starts at the 700-800 it is supposed to, but immediately increases for warmup, BUT never drops back down. But if put in first on flat ground it will move out at the 800 rpm , only to rev up to 1500 each time the clutch is disengaged or parked in neutral.  High idle was 1300 before a snapped vacuum hose was replaced.  If anyone has an idea I hope I can find the communication !    Every comment I found online speaker to idle dropping too low when taken out of neutral but my car is opposite. Perfect under power but smooth and too high to get smog test when in neutral.

[wagons]

I had similar problem. Had to replace all vacuum hoses and put a genuine subaru pcv valve in. Also make sure the idle stop screw is adjusted just right. To top it off I had to set the ignition timing, which a lot of mistakes are made doing that as the vacuum hose has to be plugged that is going to the distributor.

[skishop69]

Get a can of brake clean and spray around the base of the carb, both sides where the manifold mounts and all the vacuum lines. if the idle changes when you spray by something, there's where your vacuum leak is IF you have one. Could be timing set wrong or the wrong vacuum hose going to the distributor.

[Gloyale]

be aware that there are small "orifice" pellets inside some lines to limit vac flow to areas.  do not replace hoses without checking for them and installing them in the new line.

 

i would suggest checking the acvv  "Air Control Vacuum Valve"  it is located on the passenger side, under aircleaner, with 3 larger hoses and 1 small vac line.  It is supposed to vary the balance of air in the primary and secondary air bleeds in response to throttle vacuum. I guess to keep mixture precise for emissions.    But when it fails too much air is brought through the primary bleed. (front tube)

 

Test by clamping each one of the large hose (air bleeds) at a time and seeing if the idle changes.  If it does, the valve is faulty.  But you can trick it and smog won't even know.  find a small irregularly shaped pebble.  something that when shoved int he tube will allow just a  little air past.  

 

Round here I would remove it and put a "T" there, cap the vac line and restrict the air bleeds till it runs right.  but you need to keep it there to look stock.

[andrsn]

I had a very similar issue with my BRAT when I first got it. It'd idle up super high now and again but I could usually get it to kick down to 800 rpms by blipping the throttle. I'd second checking your timing and distributor. I replaced all kinds of vacuum junk without much luck, adjusting the timing and choke settings eventually got it running right (well, right enough to pass emissions with a lean mixture setting) but never perfect.