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.

[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.