Got a new rebuild electric carburetor. Everything went on fine, ran fine for the first few days but now it is idling very high when warmed up. I tried turning the idle down with the idle screw but the idle wouldn’t go down even when the screw didn’t touch anymore. I put the screw back to original placement and same thing. I retarded the timing alittle cause I had it advanced some cause of the way the car was running with the old carburetor. And the idle went down some but when I turned the car off the past few times it diesels some. A few putters and then stops. Could it be the fast idle? The carburetor has been engine tested so I would think everything would be ready to go right? Do I have to do any adjustments?

 

Have you checked for vacuum leaks yet?

 

Not really, unless it was tested on YOUR engine; every engine is a little different. (or even, alot)

Vacuum leaks is definitely a good place to start.

Do you have the little "kicker" solenoid on the side of the carb? What happens if you unplug it?

Put the timing back where it was and leave it alone until you solve the problem. Dinking with other things just means you have more to UNdo when you finally fix whatever really ails it.

 

So I was also having the issue that when I started the car cold. It would run for a few seconds and then die. I had to keep giving it gas to keep it running. So I checked the fuel filter just in case and changed it cause I was there. Still did it. A couple days later I figured I’d try it with the blue solenoid unplugged. Started her cold and she ran like she suppose to. I only let her rev like 45 seconds to see if she would do it and then plugged in the blue solenoid, she reved down and then died. So I unplugged her and let the car get to operating temp and plugged her back in and she idled down some but stayed running and seemed fine. Any ideas? Doesn’t diesel anymore. Or hasn’t the last 4-6 starts.

 

So I was doing some research and from past posts from here it all said to check the resistance to the MCS. She clicks when the key is on, carb was built and shipped from Napa. She only wants to die when she is cold. With the MCS plugged in I can keep her running if I keep giving her gas when she tries to die. Then when she’s warmed up she drives fine. No codes thrown. Confused on why she only does it cold?

 

Well she will not run right with that MCS plugged in. Will it hurt if I leave it unplugged? Do I need a new ECM? When I unplug it I do get a code light but she idles fine as she can. Then I plug in the MCS and she boys bad and wants to die.

 

Anyone have any ideas? I just got the carburetor from Napa, choke is how its suppose to be, the MCS clicks like it should. I have not touched the Idle/air mix screws at all cause I have never been able to adjust them right. I read on this site that that could be why my car is killing itself when i plug in the MCS? I figured since the Napa guy said its built and engine tested that I shouldn't have to adjust anything. I do not know how to use a dwell meter and reading on here it sounds like its something over my head. Should I attempt to adjust the screws? sofakindom has told me before to never touch them lmao so I don't anymore.

 

The idle mixture screws in the front of the carb basically don't do anything. The CC Q-Jet just isn't like an old Holley or something in that way. That's why I tell people not to bother with them. Just put em 6 or 7 turns out and leave em alone. They have almost no "authority"; no effect on anything.

Yes you really need the MCS to do what it's supposed to do, for the whole thing to work right.

Not sure how a dwell meter is hard to use. You hook it up and read it. There's a green single blade connector over near the blower motor; that's where you hook it to. Kinda simple really.

The way the carb works is, the ECM is constantly getting a reading of the amount of oxygen in the exhaust stream, from the oxygen sensor. Keep in mind that this is NOT a "fuel" sensor; NOT a "mixture" sensor; NOT anything else. It is an OXYGEN sensor. The system is supposed to assure that there's sufficient OXYGEN in the exhaust because that's how it knows that the fuel is being completely burned... if it's right on the hairy edge of lean, i.e. if it can lean the mixture just a little bit and sniff oxygen in the exhaust, then it thinks it know it has the mixture right. It adjusts the duty cycle (dwell) of the MCS to put this into effect.

The MCS controls 2 things: the primary metering rods, and the idle air bleed valve. The metering rods have very little effect at idle (some, but not much); the IAB valve affects idle STRONGLY, and cruise to some extent.

The MCS pulls the solenoid downwards when energized. This does 2 things: pulls the metering rods farther into the jets, such that the cruise and medium power mixture is leaner; and, opens the IAB valve, which allows more air into the idle system, making it leaner as well. With it disconnected, the system goes to full rich.

If disconnecting it makes the motor run better, then the carb is set up too lean. A dwell meter will help you dial it in. Connect it to the green test connector; at normal curb idle, it should read somewhere in the middle. Not all the way near 0, and not all the way near max. Reading in the exact middle isn't necessary or important; but having it not pegged one way or the other, is. That indicates that the computer has some room around "ideal", in both directions, to make its adjustments. It may need to be more toward one side or the other so that it has some extra "authority" to go in the other direction; but it should be well away from either limit.

If the car won't run with it connected, then the engine is telling you that ANY reduction in fuel from "full rich" is too much. I would suggest backing the IAB valve out 3 turns and seeing what that does. It's not impossible that the O-ring on it is damaged or missing, which lets in WAAAAAAYYYYYY too much air, and renders the system impotent. If backing it out 3 turns has no effect, then put it back where it was, turn it all the way in while counting the turns, then pull it out and check the O-ring. Once you are sure the O-ring is good, put it back where NAPA had it (just for a consistent known starting point, not that it's necessarily "right" although it might be), and start over.

If backing it out 3 turns DOES have an effect, and in fact helps the car run better, then it's time to use your dwell meter on it, to dial it in. I usually see best results with about 60 - 70% duty cycle at idle, which is about 40° dwell with the dwell meter on the 6-cyl scale as it is usually used. That means that the carb is a shade to the rich side, and the ECM is having to use a little bit of extra dwell to reign it in; which gives it plenty of room to move it in the rich direction, should it be necessary. It's almost impossible to make a CC Q-Jet too rich, so avoiding having it too lean is much more important.

 

Just to see where the carb idle screws where at I counted the turns and both screws were at 2 1/2. So I put them at 6 1/2 and she runs way better. Still needs to be dialed in though. A slight idle fluctuation. Not much though pretty steady now. But I never used a Dwell meter so I’m not too sure on how to use it. Every time I google it, it gives me a multimeter. I appreciate all the info though.

 

Yeah they make multimeters, one of whose functions is dwell. Just like, if you google ohmmeter or voltmeter, you'll probably get multimeters (meters that read lots of things including the thing you asked for).

You keep saying "how to use it"... it's EEEEEZZZZZZZY. So EEEEEEEZZZZZZZZy, even I can do it. And there are VERY FEW people in the world more stewpid than me; just ask any of the people where I work, or my wife, or my kids. I gotta be the dumbest blob of protoplasm to EVER splat itself onto the surface of this bizarre planet that's all polluted with corrosive oxygen from these strange self-sustaining and auto-replicating complex chemical reactions within membranes that are found all over it. All it takes is 2 steps: (1) you hook it up, and (2) you read it. It's just not that hard. C'mon man, you can DO this.

 

Been tinkering with her, seems to idle a bit better now. Sounds good on the way to use a dwell meter. Kinda nervous about backing out these air and fuel screws. How many turns do I have before it will come out? Don’t wanna back it out all the way.

 

Quite a few; but no worries, you can put it back in. Just put a drop of oil or something on the O-ring to ease its passage.

As you watch the effect of turning it out on the dwell meter, eventually it'll quite making any difference... that's the point at which it's no longer even touching the MCS armature. Remember, when the armature moves UP, it hits the bottom of the IABV, leaning it out; when the IABV is already so high that the armature never gets that far, you've passed any semblance of adjustability.

It's not impossible that the rich stop is down too far. That's what limits how far the MCS armature can move.

 

Sorry to highjack your thread but this one is very recent and sofakingdom seems to know more about this than most. High idle problems. Bit of background. 87 firebird 305 with quad. Replaced carb a few years ago, repaired all emissions controls, new distributor, all kinds of goodies. Ran great, almost 30mpg hwy, plenty of get up and go.
Fast forward a few years, gave the car to one of my daughters. She goes to work and leaves the key in on position (why?) for several hours. Calls me and says car isn't running right. I go over, its a hard start and idles at 3k. Just pumping gas like crazy. Ends up dumping so much gas down the intake it fills the crankcase and blows oil and gas out of carb.
Checked codes, shorted mcs, possible bad ecm. Ordered rebuilt carb and ecm. Fast idle down at 2200rpm, closed loop when warm at 1700rpm. That's not right, checked carb, rebuilder didn't set anything correctly. Pulled carb, made some tools and gauges and set rich, lean stops, IAB, needles, and tps. Carb back on, new plugs, cap, rotor, O2 and temp sensor. Map sensor replaced, may or may not be the right one, some debate on that. Now idles at 12-1300. Checked base timing at zero in drive, idle at 650-700, not steady. Distributor plugged in and its back to 1300 and 36 degrees advanced. Dwell meter reads zero when in closed loop. Pretty sure carb adjustments are close but still too much gas. Curb idle screw is backed out all the way. Help, I'm lost. Not sure if it's CC problem or carb adjustment problem

 

Additional info: checked for vac leaks, pulled each line one at a time and capped, carb cleaner around base, nothing. Pull line off of map sensor and idle drops about 100rpm. Used to have AC idle kicker solenoid, removed years ago without issue. Definitely running rich, can smell some gas and get a bit of dieseling when shut off but I guess that's expected at 36 degrees.
Is there such thing as retraining ecm idle speed? Ecm replaced with same pn, reused original PROM chip. Dwell reads 59 in open loop, as soon as it goes to close it's at zero (6 cylinder scale)