What could have happened to my idle on my 74 Eldo?

[collector]

I decided to clean my original wires to get off the high gloss spray that they idiots before me put on the engine. I decided to adjust the carb to 2 1/4 turns and now the car misses like no mans business. I checked the wires with an ohm meter and they are all in spec. 30 ohms for the long ones 21 for the mid length ones and 15 for the short ones. The car misses so. Only at idle not at any other operation. It drives fine and gets great gas mileage but the idle is so bad the car smells horrible. What could have happened. I had my mechanic look at it and he said it has a vacuum leak at the base gasket. How could that all of a sudden happen? Im not sure that, that is what it is. He sprayed carb cleaner at the front of the carb and the idle did smooth out. Maybe I messed up the idle screw, as we all know the idle screw is hell to get to on those engines. What am I to do?

[Ted in Olympia WA]

It hard to tell from here but if I had to guess I would say that you knocked off a vacuum hose when you tried to adjust the carb.  Or since it is a 1974 you could have carcked a hose.  I would check the vacuum with a gauge so see what it is.  There's a lot of hoses up front you they are all by the adjustment screws.  You could also try to tighten down the carb to see if it is loose.

Other thing it could be is dirt in the main jets (this could happen all at once) if it is burning lean.

If it is burning rich it could be that the needle jet is not seated.

I know I could fix it for you if I was there.

TED

[Wayne Womble 12210]

How did you decide 2 1/4 turns was correct. Adjust for best idle, not because some book says its so.

I agree you probably damaged a vacuum hose.

[collector]

No, vacuum breakage. I read if the spark plug wire has 30,000 ohm resistance then it should be replaced. I replaced one and the car does run better. I am going to the parts store tomorrow and get a cheap set until my NOS originals come. I hope that will take care of the situation.

[TJ Hopland]

My 78 had idle issues.  First problem was something in the charcoal canister let go and a bunch of little charcoal bits got sucked into the carb and ended up in the bowl causing all sorts of idle issues but it did seem to run fine.   Check the hose for bits.  If you find bits the carb has to come apart including the jets to clean it out.  If you still need the stuff hooked up for emissions testing install an inline fuel filter to catch the crud or replace the canister.   Idle got better but eventually ended up getting bad enough to stall.  After having the carb apart 3 times I had a look at the distributor and found the mechanical advance rusted solid in the fully advanced position so the thing was trying to idle at over 30*.  This also explained what I thought was a bad starter.

[greg 18360]

check the PCV hose, thats in the front of the carb.

[collector]

Ok issue resolved. I took off the carb, took out the idle screws and then sprayed out all the ports then I used compressed air to clean everything out. The outside and both inside were as if the carb was brand spanking new. There was absolutely NO carbon or junk in the intake. I replaced the gasket and turn the screws out 3 turns on both sides and then re-installed the carb. I also replaced the original fuel filter in the original fuel pump and started the car. It ran like a dream. I must have gotten some trash in the idle jets somehow. Anyway, I took it to my mechanic who put it on a dyno and turned the screws back 1/2 turn and the cars exhaust is really like fresh air. Its unreal how setting the screws to 3 turns put it just about where it should be. The car runs so smooth. I set the idle to 600 in drive but find that the idle is high in neutral. It doesn't run on as the anti-diesel solenoid works perfectly. We checked the timing and it was at 10.7 and we decided to leave it instead of playing around with it for such a small amount. I actually run regular unleaded gas not premium and the car runs just fine. Infact I drove it to my car show on regular gas for over 4 hours with the air on and didn't get a single pre-detonation ping. Its the only good thing they did in 74 to detune the car so it could run on no lead low octane gas. Im sure if I lived in a different state the low octane gas wouldn'tt work but since I live in CA, the gas if formulated to work and burn clean in all cars. I actually use 87 octane in all my cars that require 91 and have never had one single issue. Thanks for everything

[collector]

Well, I though the idle was smooth. It doesn't miss anymore and the emissions tested on the dyno as very low but I don't like how the engine runs. I guess all the 500's just had a slight idle problem. Im thinking of taking it to a pro speed shop and letting them modify the idle circuit of the carb to give me a smoother idle. If its not the carb maybe they can work on another system that can give me the results Im looking for. No vacuum leaks, all components are in excellent working order so Im sure a specialist can do something with the car.

[EAM32 17806]

COLLECTOR:  I have a 76 Coupe de Ville with a 500 engine, that I have owned since Jan 77 and it always had a very smooth idle so do not let anyone tell you that the 500 engines do not idle well.  I also rebuilt my quadrojet carburetor with rebuilding kits from TOMCO, INC. in St. Louis and I have found that their product is much better than the Delco ones I was using.  I would bet your problem is in the carb idle screws and precise timing to factory specs assuming everything else you said is in ok condition. You may or may not have an EGR valve in that year and if so make sure that is in good shape.  I know 75 up had one but since you do not have a cat convertor maybe not.  When you take off the carburetor be certain all the funnels in the intake are blown clean with no carbon obstruction anywhere.  If you are not able to rebuild or take your carb apart then maybe it is a good idea to have a PRO look at it but make sure he knows how to handle delicate carbs like these because there isn't too many of those guys around these days.  GOOD LUCK!   EAM

[collector]

I think my carb is good. My EGR is there and checked out fine. Im gonna just take it to an expert drop it off and let them do whatever and pick it up running smooth. Oh btw Ted from WA, who I have to say is just about the nicest guy a person could want to meet has posted pics of my car in the general discussion. Please check it out. Im very proud of it