Engine: 140 1986cc B20A: Rough Idle solution?

[bdhurley]

I have a question. My 144 B20A idles like a pig, engine shakes the whole car shakes, hunting up and down between 700~800rpm and the vacuum gauge needle vibrating between 20~25.

However, when I block the hose from the oil filler cap to the manifold, the engine smoothens out and runs steady at 700rpm and the vac needle gauge is holds at 20. What would be consequences of plugging the hose from the oil filling cap to the manifold long term?

About the car: 1972 144DL, B20A, Auto, 140k miles, 123ignition, compression 145psi on all cylinders, not burning oil, oil pressure 60psi, spark plugs are dry and look normal, timing set at 10°. Unmodified head and using unleaded additive religiously. Getting around 26~27 mpg which I think is very good.

I removed the head recently looking for a solution to the idling the problem thinking it was valves or guides. All the valves looked good but a few leaked with a water test. Cleaned them up, lapped them in and retested, no more leaks. There didn’t appear to be any noticeable ware on the valve guides. Cleaned the head and the pistons, there was no lip in the cylinder walls. Cross hatch on the cylinder walls was faint though.

Service history is compresive from 1974~1986; Had major work done in the mid '80s.

** May-1983 @ 126k miles “Decoked, new valves, springs, guides, points, kick down cable, engine oil, transmission oil, rear axle oil, lubysil added. New plugs, water pump, fuel, air, oil filter”

** April-1985 @ 128k miles “Removed and rebuilt the engine, new piston rings, main shell bearings, big end bearings, oil filter, automatic oil pump”

Last service entry was in Dec-1986 @ 132k. I got the car in 2018 with 137k and I have put a further 3k on it.