Wheat

Hey guys! New user here. I've browsed these forums a lot in the past to find lots of great answers and tips, but I've finally landed on an issue that I can't seem to find an answer for.

TL;DR version:
I have an '87 Civic sporting the carbed EW2 with 140k on it that has an idling issue. It takes a second to crank up, but once it does, it usually kicks up to the fast idle (~1800rpm) without issue and will idle pretty steadily there until the engine warms up. Once it switches to the regular idle though, it will waver between 650-800rpm for about 10 seconds, then dip dramatically (often stalling if I don't kick the accelerator a little) and then recover for another 10 seconds before dropping again.

I've cleaned it up, had the oil and oil filter changed, run a fresh tank of gas through it, and visually inspected all of the major engine components (if that's too vague, read the long version below), and all that I can see that's wrong with it is a very mild oil leak.

I've temporarily reduced the stalling by just tightening the throttle cable to the point where it idles higher (~1100rpm). Yes, I know that this isn't a great solution, but it drives a little safer when I don't have to heel/toe or use the handbrake at lights and stop signs to keep it from stalling. Also, if its any help in the diagnosis, after tightening the throttle cable it 'idles' more steadily, and only drops threateningly if I have the air conditioning on, while braking, while going downhill. If I do all three of those, it sometimes stalls, but otherwise has been running fine.

I'm guessing that its an issue with a valve in the carb, but I don't wanna go taking apart a carb or ordering parts until I have a better idea of what the issue is. Please help!


Long version with all the juicy details:
So my GF really needed a set of wheels (she's a full-time student with rent payments whose part-time job just closed up shop) so I found her an '87 Civic sedan with 140k miles for $800. My mom's car while I was growing up was an automatic of the same year and model, so I knew how fun the car was and how many miles you can squeeze out of em. Plus, I'd helped my dad do a lot of service on the thing when I was younger, so I felt pretty familiar with the thing. It only had one previous owner - a veteran Adult Swim animator and the voice actor for Zorak and Moltar from Space Ghost Coast to Coast and Dr. Weird and Steve from the ATHF intros! Here's a Road & Track article about the car I ended up lucking out on.

I was impressed by the low mileage and relatively clean condition of the car, so after test driving the thing I happily handed him $800 and took it home. I noticed that it had a hunting idle on the low side, and I chalked it up to the carb being old and probably a little sticky since the car hadn't been driven in 2 months... But after getting the oil & oil filter changed, running a fresh tank of gas through it, checking the timing belt, checking the air filters, checking the seals on all the vacuum lines I could get to, and visually inspecting the carb and engine for any leaks, the only issue that I've positively identified is a very slow oil leak around the oil pan gasket (slow enough that I've never actually seen it drip, there's just a gradual buildup of oil residue around the compartment). I haven't been able to check if there is air in the coolant lines, as the bleeder screw is badly chipped and I'll need some vice grips to remove it, but from what I understand, air in the coolant is more likely to make the idle rev higher, not dip to a stall...

It takes a second to crank up, but once it does, it usually kicks up to the fast idle (~1800rpm) without issue and will idle pretty steadily there until the engine warms up. Once it switches to the regular idle though, it will waver between 650-800rpm for about 10 seconds, then dip dramatically (often stalling if I don't kick the accelerator a little) and then recover for another 10 seconds before dropping again.

I've temporarily reduced the stalling by just tightening the throttle cable to the point where it idles higher (~1100rpm). Yes, I know that this isn't a great solution, but it drives a little safer when I don't have to heel/toe or use the handbrake at lights and stop signs to keep it from stalling. Also, if its any help in the diagnosis, after tightening the throttle cable it 'idles' more steadily, and only drops threateningly if I have the air conditioning on, while braking, while going downhill. If I do all three of those, it sometimes stalls, but otherwise has been running fine.

I'm guessing that its an issue with a valve in the carb, but I don't wanna go taking apart a carb or ordering parts until I have a better idea of what the issue is. I know that the vacuum hoses tend to get badly cracked and leak, and that the gaskets around the base of the carb can crap out, but I haven't seen any leaks around the base of the car, and I can't hear even the slightest hint of a vacuum leak...

Please help!


Thanks a million,
-Wheat

Wheat

Oh, and I just realized that I completely neglected to mention that it is a manual.