Pulling my hair out (if I had any)!, Surging idle that won't go away Options

[mpoffers]

I've had this 75 1.8L 914 for nearly two years and I have yet to get a decent idle. When I first start the car it revs up to about 1800 rpms. After 30 seconds or so it dies. If I set the idle adjustment high enough I can get it ot to keep running, but even then it ALMOST dies, then surges up to 1500 or so, then cycles back and forth. With the idle set high it is reluctant to rev back down when I let off the throttle.

Other that that, it runs pretty well. It pulls strong as expected at all revs. It's fun to drive, but blipping the throttle gets really tedious in any sor of traffic. It even passed Oregon DEQ. The idle problem isn't as bad when the engine is hot, but it is still there.

Per advice from you guys, I did a valve adjustment, set the dwell, checked the timing, replaced fuel hoses, and replaced all the vacuum hoses. I replaced the gaskets on the oil filler (flat and o-ring). I tried spraying suspect connections with WD-40, but no of them caused a surge.

What's left to try? Can I start disconnecting and plugging things that aren't needed at idle (decel valve or emissions stuff) to try to narrow down the problem? I suppose I could take to A&P in Portland, but I hate to admit defeat.

[Root_Werks]

I'm not all that informed on the L-Jet stuff, but that sounds like a vac leak. Hoses are only a small part of the components that could be leaking.

If you have a little propane cyl for soldering, use it. Turn it on and run it around intake parts. If there is a leak, the rpm's will pick up.

[TheCabinetmaker]

WD-40 won't do it. Takes too long to vaporize. Use carb cleaner or starting fluid to find the leaks.

[tradisrad]

dont know much about the L jet, but I do know that the engine needs to have no leaks including the oil cap

[charliew]

The propane torch without the flame, works good on vw motors to find vaccum leaks.

[Als914]

I had the very same problem years back and did everything you did with the same results you are experiencing (IMG:style_emoticons/default/headbang.gif) .

This is what I did (wright or wrong) to solve the problem. I pulled the throttle body out and checked for any leak source and found, 1) no gascket to throttle body and plenum mating surface, 2) backed out and removed the idle adjustment screw and noticed it had what appeared to be an o-ring seat at the top near the head. I could not find a gasket to buy so I improvized and used a silicone sealer on the inside surface of the throttle body, let dry before assembling. I then took the idle adjusting screw to a local o-ring shop and bought several that might work. Through trial and error and after tearing several o-ring I found one that fit, all be it tight. I then started my '74 L-jet and adjusted the idle to 900 rpm's where it has been ever since.

After the initial test period of a month of daily driving ( fouty-eight miles, one way)California freeways (IMG:style_emoticons/default/driving.gif) I removed the thottle body and made a very thin rubber gasket to replace the silicone sealer.

I wish I could give you o-ring size and gasket thickness but I did this about ten years back but I hope this helps resolve you erratic idle like it did mine.

[Bartlett 914]

I would start with the AAR valve. It should be slightly open when cold. The electrical heater inside should close off the valve in a few minutes. They can stick open or closed.

[detoxcowboy]

generally a surgeing idle is too lean, richen your mixture until it stops surging, do so after the car has warmed upp 15 min. or so

[bjsomers@gmail.com]

I have the exact same problem with my 76 914/4 2.0L, were you able to find the fix?

brian

[budman5201]

generally a surgeing idle is too lean, richen your mixture until it stops surging, do so after the car has warmed upp 15 min. or so

I agree. Recently even with my ez30r subaru engine I was doing an auto tune with my link computer and accidentally typed in a 18 fuel value where a 48 value should of been during idle on my map. The car surged lower went below that value on my fuel map until it hit a richer value and then did surging higher to lower trying to steady itself out. I bet that's what your computer is trying to do.
It's prob got a vacuum leak somewhere other than the hose connections and the computer is trying to compensate.

I agree, get her warmed up and use propane gas and u should get a general area from where it's coming from.

Hey can we see a few pics of your engine bay? Maybe after working on crap so long u don't see it. I've had u guys point me in the right direction a ton when I couldn't see or find anything.

[Markl]

I have D-jet, so may not apply, but a new CHT solved the exact same problem. I had spent months trying to find a vacuum leak!

[avidfanjpl]

I have a 2 liter, and had that AAV problem, mine was dead. Put in a new one and it seriously fixed the idle on the spot.

Test yours by yanking it applying 12 volts to the red wire and negative to the body. It must heat up on the bottom of the AAV in a few minutes, or it is dead.

If it is dead and you want to, you can put a 1/3 inch ball bearing in the hose coming from the air cleaner, and it will solve (until you can get an AAV that works) your idle problem BUT LET THE CAR SERIOUSLY WARM UP OR YOU WILL KILL YOUR BEARINGS BY RUNNING A COLD MOTOR!!!!!

I can not be more serious about truly letting the engine come UP TO TEMPERATURE.

I ruined a motor by running it cold in 1979!!!

Good luck!

John
avidfanjpl