My 1983 Continental Mark VI!

[gadget73]

vac leaks and O2 sensor are pretty good bets if you know the ignition parts are in good shape and all that.

[mercurygm88]

Yeah I have the vacuum operated throttle kicker for when the A/C is on. Sometimes it works sometimes it doesn’t. It just has a vacuum line going to it and I’ve never traced it but I’m guessing the other end goes to an electric solenoid and that’s only working intermittently.

[Arquemann]

EEC-IV goes to some predetermined fuel maps if it doesn't get an O2 signal. Richer than normal to stay safe. I'd believe EEC-III would do the same.
You probably could unplug the O2 and see if the MPG goes even worse

Does your car have a vacuum dashpot to bump up the idle when the AC kicks on? Anyways, when I had my EEC-IV CFI, I had the idle at about 550 rpm in gear, wouldn't stall pretty much ever, but the car idled a whole lot smoother at about 600 rpm, but then the park/neutral idle felt kinda high...

[mercurygm88]

Ok so I'm guessing the answer to this question is going to be something along the lines of "It's EEC III CFI, you're lucky it runs at all!" But I'm going to give it a try anyway. When I bought the Mark VI in June of 2021 and did the initial tune up plugs, wires, cap, rotor, fuel filter, air filter, oil change I was getting about 18-19 MPG. Sometime between last summer and this spring that dropped to about 13 MPG. It runs good, idles good, no drivability issues, the plugs look fine. I'm guessing maybe 02 sensor? The only thing I've changed in that time was doing a smog delete and I can't say with any certainty that the drop in mileage happened at that time, but based on what I've read I'm guessing that has nothing to do with it. I feel like I read somewhere that a bad 02 sensor will cause a drastic drop in mileage with a CFI engine while not causing any other noticeable issue. For $20 I figure I might as well replace it anyway.

[mercurygm88]

I haven't had time to mess with it lately. I'm figuring the ancient off brand "ignition analyzer" I was using for a tach is probably wrong. I have it set high enough that it doesn't bog down when the A/C cycles but it also doesn't bang into gear. Good enough for me.

[kishy]

Cold idle is bonkers stupid high, like 2100 or something. I got mine to idle at about 1800 rpm with no fuss. Warm? 550 or so in gear, I can't remember the actual number, pretty sure the sticker calls out idle in gear when hot. Does yours not have the little sticker on the fan shroud? That should have that information listed. Hopefully kishy will comment here, he'll know.

You're just about on the nose with the 2100 and 550 figures, as I recall, but I don't know if EEC-III wants something different. It's the same throttle body as EEC-IV but the computer is as different as it gets.

The sticker on the fan shroud will have this information, and if it's damaged or missing, hopefully another EEC-III car owner can chime in to verify. The service manuals all say to look at the sticker for this sort of thing.

[DerekTheGreat]

Cold idle is bonkers stupid high, like 2100 or something. I got mine to idle at about 1800 rpm with no fuss. Warm? 550 or so in gear, I can't remember the actual number, pretty sure the sticker calls out idle in gear when hot. Does yours not have the little sticker on the fan shroud? That should have that information listed. Hopefully kishy will comment here, he'll know.

[gadget73]

it actually should be on the emissions label under the hood, probably both low and high idle and under what conditions

but it shouldn't sound overly fast. The tach might lie, or it may be some unrelated noise making it sound funny though. Another clue the idle is too high is that it will have a very hard engagement into D or R from park.

[sly]

Idle in park for SEFI cars is 675 +/- 50 rpm so most people shoot for 700 and will take 650. I'm sure CFI should be similar.

[gadget73]

typical idle on a V8 of any make or induction system is in the 700 range. Agree it sounds like your tach is lying.

[jaywish]

IDK those cars in specific but 550 is generally a low end idle speed in park. What are you using to verify speed?

[mercurygm88]

Does anybody know what the correct idle is supposed to be for an EEC III CFI 5.0? Mine is at about 550 and sounds like it's awful high. People on other forums are saying 700-800 in park, I don't think so.

[DerekTheGreat]

Wow, "auto show worthy" huh? You are too kind, thank you sir.

[kishy]

This engine bay is actually really clean in person.

Derek's just rubbing in the fact that he puts shoe shine or whatever on his entire gleaming, auto-show-worthy engine bay. Yours looks really good for a driver.

Mine are all disgusting.

[mercurygm88]

A warm air intake!

Well you see the factory air box snorkel disintegrated within a month of me buying the car. This looks better and can't be any worse. There's how many millions of engines out there with them?

I'd power wash that engine bay, I'm getting choked up with dust and dirt all the way over here.

This engine bay is actually really clean in person.