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Discussion Starter #1
My 86 305 shakes alot at idle and when I am going a steady speed the car kind of feels like something is pushing it back and forth. I thought it was a transmission problem because when it starts to shake and I hit the gas ever so slightly the tranny downshifts( the tranny is a overdrive auto.), and the shaking kind of stops but when I let of the gas the tranny up shifts to overdrive and it starts alll over. A man at the Autozone said the problem is a Limp cylinder, and to fix it I have to replace the spark plugs and spark plug wires. But after doing that the elky still does it but not as noticable. Has anyone ever heard of this or was the clerk just trying to make a sale? I have no idea how to fix it. is there something else that I can replace or check?
 

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My first advice would be to go back and recheck to make sure that all of your wires are tight, and in the right position.

Next I'd check the wires to see if they're firing at the plug, there are a lot of methods for doing this. I personally turn off the engine, pop a plug wire, and stick a spare plug into the boot, then I hold it against the fender well, or a good ground and have someone bump the engine. (I definitely recommend a good pair of insulated pliers for the job. Don't want to get zapped.)

If you can see the plug sparking really well, then put the wire back on and try the others. If you see one that's weak - try a different wire - if you have one. (It pays to keep your old ones around sometimes.)

You might find a bad wire, or one might not have been assembled properly.

If you are getting good fire to your plugs, the next thing to hunt for would be a vacuum leak somewhere. Check your vacuum lines, hoses, etc... also check your PCV valve, and your EGR valve (assuming it's there.)

Also, check your base plate on your carb for vacuum leaks. Lots of theories on how to do that. I usually just spray a little starter fluid (some people say WD-40 - less flammable I'm sure.) around the base plate area - if your idle smoothes out, then you might have a base plate problem.

Those are just places to start.
 

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Discussion Starter #3
I checked the wires and one of the wires was warped and broke. After I replaced the wires the idle did get better but after driving for a while the problem started to come back just not as noticable.When I spray WD-40 or carb cleaner in and around the carburtor the idle does calm down but the engine still shakes I will check for vacuum leaks as soon as I can.
 

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Sounds like you're on the right track. If you find any vacuum leaks, take care of them. If the problem persists, post back here, and we'll try to think of something else to try.
 

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it sounds like you need to do a complete tune up or at the very least pull the plug that you had the broke wire on since it wasnt getting any fire its probablly gunked up or fouled.
 

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Discussion Starter #6
How can I tell if I have a EGR Vacuum leak. what do I look for and how difficult is it. Im Just not familiar with newer cars. First V8 caburator car is a 69 chevelle.
 

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EGR valves normally won't leak, but if they do, you'd hear them hiss or breathe. A lot of times when an EGR valve fails the EGR valve will get stuck. You check this by seeing of the diaphragm inside the EGR valve moves.

I know you can check it by removing the valve and trying to physically actuate the spindle to compress the diaphragm. I can't recall if you can do so without yanking it by trying to move it through the gaps in the bottom side of the assembly. (I'll try to check my manual on that and let you know - if someone doesn't correct me prior to then.)
 

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EGR runs off of vacuum. Go to an auto supply and get a cheap vacuum bleeder / tester. Looks a little like a plastic gun with a gage. Hook that to the EGR vacuum line and pull a vacuum. If the diaphragm moves its probably not bad.

Start off this time by going to the same auto supply and pick up some vacuum hose. Replace all the lines on the truck. Believe me it is easier this way. If you do a one at a time thing it can take a while plus every other vacuum line is about the same age. This will make sure that you have good lines and remove that from the process of troubleshooting.

You can pull the Carb plate off of the intake by tightening down the Air Breather lid screw too tight. this will create a leak that is almost impossible to locate. All you need is to have that wing nut snug don't torque it. It is especially problematic with Q-jets. They have a very thin wall between the front and back throttle plates and it will bend pretty easy.

If you have a leak there now, change the gasket add sealer, what do you have to loose. If you want to find a problem with firing or Air/Fuel mixture then look at the plugs after you've ran the engine a while. Let it cool off and one by one pull each plug out. Look to make sure they are not fouling, black will generally be oil especially if it is starting to cake (Collect on the insulator) If they are wet and your exhaust is burning your eyes then your defiantly not firing right.

If all the plugs come out a very light gray with a very thin black line in the ground strap then it is firing alright on each cylinder. Next do a leak down check. This will eliminate the possibility of things like a bad or burnt valve, bad or broken rings etc... If a valve is bad you'll hear it leaking back and with that compressed air you'll pretty much be able to check the head gasket also and isolate which cylinder is leaking by listening.

If you go through all this and everything seem correct and your still getting a rough idle then pull the distributor look at the gear see if it is worn excessively. You can buy a replacement gear. Then possibly your timing chain could be stretched out.....

Just some of the stuff I'd look at if I was having the same problem. Cam lobe could be flat, lifter is not operating right, lots of stuff can cause a rough idle. Computer cars could have a faulty AIR sensor, MAP/MAF, Cat can be choking it, TFE could be stuck, crack in the distributor cap, Rotor could be arcing to your distributor .........

I'll quit. :D
 
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