I've been fighting my idle since I got my car running this past summer. At first I suspected it was vacuum related and I was correct as a bunch of the ports for vacuum were either not linked right or sealed. Took it to the mechanic for a look over (nice to have someone look it over after 7 years of working on it on and off) He found a couple more vac leaks and refined the timing and adjusted the carb. Said it ran like a dream and it did. But when I came to a stop at a light it would die. Vac leak again. This time the vac leak was in the Emissions system as my AIR Injection pump was completely broken. (in two pieces) I figured I'd either remove it or fix it but my heater core took priority over that. Once the heater core was fixed I went back to the leak, but my smog pump siezed up. Because the pump seized up I decided to remove the entire thing hoses and all. I capped off the AIR lines at the exhaust manifolds. Now that was fixed I had a high idle again.

Now I knew it was vacuum related but I kept looking for a leak and didn't find one. Talking to a family friend he said that I didn't have a leak but rather too much vacuum. His advice was to back off the mixture screws and that should alleviate the high idle. Now I believe he might be correct as I think the car is running rich again, and also I believe the high idle returning coincided with the removal of the smog equipment hence the extra vacuum.

The question I have is if I do need to back off the screws for the mixture which way do I start turning them to back it off? The car in question is a 87 LG4/84 L69 Hybrid (not literally a hybrid, as it still runs on pure gas) with L69 exhaust, carb, accessories, and LG4 internals, block, heads.

I might find out myself where I need to go with it but.....rather be sure. Thanks.

 

You can never have 'too much' vacuum. On a mechanical carburetor one would tune the idle mixture screws for the highest vacuum reading on a vac gage.

Your carburetor is the original computer controlled q-jet, right? The ECM will control the mixture as long as it's set within a specific range so don't go changing any settings unless you've got a dwell meter or scanner to set them properly.

When it idles high have you verified that the throttle stop is resting on the idle set screw, drivers side of carb? The set screw is the one with the spring on it in this picture:



If it's not bottomed out against the set screw when high idling, check that the choke linkage on the opposite isn't holding it up. The choke is designed to keep it at a higher idle during warm-up then allow it to drop down but the choke linkage will sometimes get gummed up and stick or fail. The choke will be off when the choke blades are pointed 90 degrees straight up.

Another increasingly common problem on these older q-jets is worn throttle bushings. As the bushings on the primary throttle shafts wear the throttle will sometimes stick partway open and/or the carb will develop a slight vacuum leak at the shafts.

If your throttle is completely closed when it high idles (and you haven't dickered with the idle set screw) continue checking for vacuum leaks. Plug every port on the carb/manifold and reconnect them one at a time, better yet 'rent', for free, the mityvac vacuum tester at AZ or one of the others and check your vac systems.

 

Yes it is the original computer controlled carb. And I still have the original L69 Computer. I did some looking around and I understand what you mean about the too much vacuum. As far as I know the screw on the throttle linkage hasn't been messed with by me. The idle and air fuel mixture screws to my knowledge are sealed at the factory. However on mine, and the LG4 carb that I still have from the donor motor (wiring harness didn't match up so it was pointless and I wanted to use the original L69 carb.) the caps for those double D screws are long since gone. Thus I'm suspecting that the double D screws have been messed with at some point in their lives. I am wondering if turning those screws might settle down the idle like it would on a mechanical carb. My understanding is they work the same way. Also like I said the car seems to be running rich as well, and that condition I think is fixed by turning the main screws as well. Now looking at how cold it is it might be a warm up. But how long does the motor have to run with the choke open at 2000 RPMs to warm up? Having been around cars with Manual chokes it can't be that long. Thing I don't want is I don't want to run around with the car idling at 2000 or dying on me as I come to a stop. Therefore I want to get the tuning on the car right before I drive it any significant distance from the house.

I threw the choke linkage wide open 90 degrees, and then put my finger on the port that goes to the air cleaner. When I throw the throttle wide open the secondaries snap shut, from their 90 degree opening. I suppose it is possible that the choke is sticking on me and not stepping down. If that is the case then how is that fixed. I know I had the choke thermostat replaced and when I first tried to start the car to make it run I had to throw the choke wide open. So I guess the question is as I said before how long does it typically take for it to warm up then step down to a 750 idle? Looking at all of our other cars it can't be too long.

 

The carb is computer controlled and will not react to adjusting the idle mixture screws like a mechanical carb. Leave them alone for now.

Don't chase down a choke issue until you've verified that the choke fast idle cam is holding the throttle off of the curb idle set screw shown in the photo above. The fast idle cam is beneath your choke linkage. If you suspect it's keeping the throttle off the curb idle set screw you can move it with a screw driver (or other handy pointy thing) so that it's no longer engaged to see if the throttle sets back down. If all of that choke stuff is gummed up, get some carb cleaner and spray it down good.

When you say 'secondaries' I have to assume you mean the choke plate above the primaries? Snapping shut when the engine is cold when the throttle is opened is normal. That's how the choke is engaged and why the starting instructions say to press the gas pedal down twice before cold starting.

Your choke plate should slowly open as the motor is running and take around 2-4 minutes to open completely. After it's open the throttle will have to be blipped to take the idle off the fast idle cam position, dropping it down to normal curb idle.

 

Ok so I guess the first thing I should do is start it up, and let it run for a little bit. Make sure the choke plate opens, then when its fully open blip it and see if the idle drops back down. I guess part of my problem is I'm used to running around FI cars so some of the carb quirks seem out of wack to me. It could be possible that what I think is a high idle might be the warm up and I'm not letting it run long enough to get to the completion of the warm up stage and drop back down to a 750 idle. So in reality there could be nothing wrong in the first place.. we will see. I might try that this evening or sometime soon.

 

Ok, I fired it up today, (it hit a whopping 32 degrees today) let it run. Now, I love trickle chargers. It fired right up as soon as I got gas to the carb. I let it run for almost 6 minutes. Upon startup it idled at 2000-2100 RPMs. After letting it go through the warm up cycle I noted that the choke plates were vertical. I punched it and it dropped to where it should be. One would think that would be the end of the story. However, it seemed to raise more questions than answers. No sooner had it dropped to somewhere in the 800 range (might be a lil lower) it stalled out. I promptly started it back up again and it went back to its idle of somewhere around 1000. Feathering the throttle in N I was able to maintain the idle at 750. However, when I took my foot off it stayed there for a couple seconds then stalled out again. Now it was getting cold so I decided to end the experiment and shut down and close the door for the day.

Does anyone have any more ideas as to what this would be? The car has plenty of power no doubt. But I thought I could hear a chuffing or clicking sound from the engine bay. Another pulley going bad? No leaks, and a lil smoke from the water pump (belt might be slipping). I highly doubt this is a terminal issue. I'm thinking rebuilding the carb will no doubt fix or repair any vacuum leaks, and providing I don't miss any lines should eliminate vacuum. Any further input would be appreciated. Thanks.

 

Ok, I'm told that it is impossible to get the ccc Q jet, HEI distributor and L69 computer to work right unless you have a cat, O2 sensor, and all the smog equipment, and sensors in place and working. Right now I've got rid of the smog pump, capped off the AIR lines on the exhaust manifolds, no cat converter. But I am still running the ccc Qjet, HEI distributor, all the sensors on the carb and intake, O2 sensor, and all the other emissions vacuum system. Is it even possible to make this work? I know it ran great over the summer when it was running so I am not sure.

 

You can run without the smog pump, no problem. Ditto the converter. ECM won't care. Just like dogs don't know that "begging strips" aren't bacon.

Keep at it with that low curb idle stall-out issue. If you can idle it that low for a few seconds then it stalls, something's not right. Like was said, above, you don't want to mess with the idle mixture screws UNLESS you know they have been (mis)adjusted previously. If that's the case and you need a "roughly right" setting to get you back in the ballpark, 4 turns out each from lightly seated will get you close enough in most cases.

It's possible on a cold day with the factory air cleaner off you could be getting some carb icing (factory air cleaners have that hose that draws hot air off the exhaust manifold heat stove in cold temps). Carb icing does no permanent damage, but it can make low speed idling miserable until the engine warms up FULLY. Like 5-10 miles of driving. Just becuase the coolant is up to temp doesn't mean that the carb and intake manifold are yet. That's why factory air cleaners have that hot air hookup in the first place.

Check your ignition timing again yourself, using factory-recommended procedure. (Basically, you check it with the 4-wire in-line computer connector behind the distributor/above the tranny bellhousing disconnected).

 

Ok so it can be done as I thought. I am probably going to backtrack to square one and check my intake manifold gaskets, per the factory diagnostic chart in the service manual. I know I replaced the carb mount gasket. That should eliminate the possible vac leak in the manifold. There are a couple of vacuum lines that are badly cracked, I'll replace those, so I know there is no leak there. Once I am satisfied there, I will go back and recheck the timing. The only other thing that I can do that I haven't crossed off yet is the carb idle screw. Which screw is that one? The one on the throttle stop or the one by the choke? That could be out of adjustment. The mixture screws I will only touch as a last resort. I know they have been messed with as the factory plugs are gone.

Now for the sake of the discussion. Lets say that I can't get this right with the computer and I tried everything. I was looking around at going old school, with a pre CCC Qjet and a HEI vac advance distributor. That would probably eliminate everything electrical and throws the emissions stuff out the window. I found a few carbs of late 70s vintage off Pontiac 400s, Olds 403s, Chevy 305s and 350s. I am assuming any one of those will bolt on top of my 305 manifold. The question lies with the distributor, if I do decide to go forward with this (price sounds reasonable and the bonus of just using screwdrivers to adjust it with the possibility of more power) which HEI vac advance distributor do I go with?

 

Curb idle is the one in the pick above.

You really need a dwell meter to adjust the idle mixture screws in the base.

Regular replacement large cap HEI with mech/vacuum advance will run around $90 or so.

Won't get any more power out of a mechanical qjet/dist. The secondaries (which feed the carb at full throttle) are the same as the ccc-qjet. You'd also be tuning by replacing primary jets and needles instead of letting the computer do it for you.

 

Ok so I could mess with that screw in the pic above. Would a Poncho Qjet fit on a 305 manifold, and what distributor would work if I wanted to abandon the electric one? 350, 305, 327, 400?

 

Ok, forget the Poncho Carb swap, it would work but it might be a mute point. Someone on the Early Third gen boards said she wasn't sure but it could be the TPS sensor going bad. Considering the fact that I've rebuilt or replaced just about everything ignition and starter wise that was actually not a bad idea. I mean if my distributor had bad corrosion on all its parts no doubt the carb could have the same problem with its electrical points. After all it did sit on a shelf in an ordinary garage (not climate controlled) for five years, as did all the other electrical parts.

 

Five7 told you to keep the ccc-qjet didn't he?

You can test the TPS with a DVM or voltmeter-I can walk you thru it if you'd like. The other soft parts of the carb could probably stand replacing though if it's sat for that long. There's tons of threads on rebuilding the ccc-qjet-be sure to read through them before tearing anything apart. You'll want to count turns to seat on the IAB and lean stop (MCS) set screws when you take it apart in order to reseat them at original height. I can point you towards some help if you need it.