1983.944.newbish

Ive dumped a ton of time and resources into this car for my son and thought I had it! Vacuum lines were switched at the coolant temp sensor under the manifold. Hard start before, but upon switching the front and back lines it started and ran pretty good. Took it down for an oil change, and man now it runs rough. Looking under the hood I found a Vac line disconnected that ran by the oil intake and reconnected it. But it has developed a low idle condition that sounds like its choking out with a scraping noise as well. it seems ok as the RPMs increase, but let up on the throttle and it goes back to low idle shaking and shuddering. I had ordered new plugs,cap, wires and rotor, So I installed them and it changed nothing.

But now Im at a standstill, I dont know what to do next. I dont believe its a Spark problem, or a vacuum routing problem. it changed so drastically though. I supplied the oil, and it honestly sounds like the lubrication is not right, but thats crazy right? I used a Synthetic 10w50 but it had graphics of motorcycles on the bottle and so I just dont know.

Any Ideas?

Gage

Sounds like a classic vacuum leak to me. I suggest getting a vacuum gauge reading at idle. If not at least 16", a smoke test will identify where the leaks are.
FYI, the tubing connections at the "rabbit ear" thermo switch are reversible without change so no smoking gun there.

1983.944.newbish

BET, I will run through it again. I may be best served replacing the brittle ones anyway and since I have read so much on the routing I feel like I know exactly where Im at, SO thats when I usually come up with my AHha moment.
Thanks

Gage

Remember that vacuum leaks are sources of false air, air that can enter the engine without being measured and can occur anywhere downstream of the air flow meter (AFM). This includes the auxiliary air valve (AAV) and air oil separation (AOS) hoses, devices and connections as well as connections to and from the intake manifold. Any hoses that are cracked or brittle will need to be replaced which often requires removal of the intake manifold.
Measure the pressure in the intake manifold. Posting photos of the engine may be helpful for diagnosis too.

1983.944.newbish

r

Good reminder of the large hoses as well, thank you. The gasket o ring around the throttlebody adjustment screw was disintegrated and getting unregulated air. I replaced it and it helped. But the main concern now is after a rev, the idle Will drop below the low idle line, say idles @1000, and once You fluff the pedal as it returns back down it will drop to 700 before returning back to the thousand. Which makes it very difficult to fluff on a hill and keep your power. Here is a YouTube of how it was running before the o-ring replacement. And the after video is the drop in RPMs I'm worried about. Ive replaced the cap rotor wires.



I have mechanical experience but I'm no expert. This pre ODB situation takes an ear that I don't possess and I could use the help where to turn next.