So lots of variables make this issue challenging:
Tried to start the car too fast, releasing the ignition-key too quickly for the starter to complete its job and the engine stuttered to a stop. Next I started it properly and the engine was now idling quite rough (continuing roughness until about 20 mph) and making a super-high-pitch whine/squeel sound (like a strong vacuum leak through a tiny hole.)

After about 20 minutes the check engine light came on with engine codes: P1316 and P0300-P0308 (misfire on each of the 8 cylinders)

I cleared the codes and idle instantly got smoother, but the roughness returned when I drove more and then no new codes, but 2 pending codes: P0171 and P0174 - System too Lean (Bank 1 and Bank 2)

I checked the oil and found it very low (the last few millimeters of the dipstick), added 2-quarts and it only brought it just above the "low" marker on the dipstick. No recollection when I last changed the oil either

This happened about 2-hours after getting engine work done, swapping out the ABS-module (via sliding it out without disconnecting any brake lines.)

From searching this forum for the codes, it sounds like I may have a leak in the plastic air intake to the throttle body, would that cause a rough idle and misfire?

Ideas?

 

Check your part load breather tube on the driver's side at the top of the valve cover first. This tube is brittle from age and easily broken if knocked while the ABS unit was being replaced. With the engine idling you can use a rubber hose held to your ear while moving the open end near the breather tube or around the engine to pinpoint a vacuum leak


Don't drive the car until you find and repair it - it is not worth the risk of serious engine damage

 

Your advice seems to be a bulls-eye; now how do I fix/replace it? I've duct-taped it back together but have yet to start the car (and my tape-job is definitely not air-tight.)

Also, does that mean the low-oil was a coincidence and unrelated?

 

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How do I connect to the throttle body side without removing the whole throttle body?! Just channeling it down the length of the engine-block looks tedious...

 

Is it possible to tie a piece of line to the end and use that to pull the new one through? I have not had to do this yet, and pulling the manifold seems like a nuisance. But then, it's also a good opportunity to replace the cooling hoses also.

 

I think the low oil level was unrelated and a coincidence