Rough idle...

53ryder

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I've a 1987 5th Avenue, with lean burn gear still attached and working (I hope). Owned since last November. Car has about 101000 miles on it. No issues until about 2 weeks ago when it started idling very rough. The car really shakes.
I replaced distributor cap and rotor and plug wires this morning. Can do plugs today as well. Car starts up fine but still a rough idle. What should I think about next? I am a novice, but willing to learn. Any thoughts?


Glenn
 

JBFury

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I had similar issues with my 82' Gran Fury. Cap, rotor, wires and plugs were all replaced and it resolved the issue fully. I think not doing the plugs is why you're still having an issue.
 

53ryder

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One question on plugs. Have done them before several times on other cars. Ordered these Bosch plugs from Rock Auto. A different kind of tip, supposedly fits my 5th Avenue. Okay to use or get some more 'traditional' tipped plugs? I dunno!
IMG_4134.JPG
I've just never used this kind of tipped spark plug before. How about you all?
 
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JBFury

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I've never used that type of plug, so I'm unsure. I personally just stick to the classic style so I can accurately gap them and install.
 

Mikes5thAve

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I've always used plain champions or ngk splitfire. Platinum plugs and other modern stuff doesn't have much benefit in an old engine and can actually be a negative.

If its never been touched it could also be a carburetor problem but its best to start with the simple stuff. Checking the slack in the timing chain might not be a bad idea either.
 

69-

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There might just be a loose/brocken vacuum hose. Remote diagnosis is hard. Just do a routine check of it all, starting with easy things.
 

Aspen500

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As mentioned, the multi ground, iridium, etc.. plugs don't seem to function well in older engines, especially with stock ignition systems. Personally, I'd go with plain old copper core, regular plugs in your car.

One thing came to mind. Does it idle rough/erratic or is it a dead miss? If it's a miss, and not ignition related, a burned valve can cause the symptoms. It'll miss at idle but smooth out above idle (unless the valve is burned half away). They have been know to come on suddenly. Hoping it's not your problem though, and highly doubt it is.

Like 69 said, go over all the vacuum hoses carefully, looking for cracks, splits, or disconnections. A vacuum leak will also cause a rough idle but will be smooth off idle. One other is if the charcoal canister interior mesh ruptured and then charcoal specks can make their way into the fuel bowl and plug, or partially plug, an idle port.
 

LSM360

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I agree Aspen500; Just use the Champion RN12YC. Just what your engine wants. And I also doubt it's a burnt valve in the venerable 318. You need to go through those old hardened vacuum lines.
 

Camtron

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On top of the checks others have mentioned, your EGR valve could be a little dirty/clogged and sticking open a little bit.
 

MoparDan

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I once put Bosch platinum plugs like those on my old '82 Fifth Ave: big mistake! They were fried in a month...replaced them with the Champion copper plugs the others have mentioned and that's all I've used since
 

53ryder

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Appreciate the input! Will get some Champions and an EGR Valve and start checking all those yards of vacuum lines!


Glenn
 

Mikes5thAve

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Don't need to get a new egr valve yet. You can test it by pulling up on the shaft with a screw driver at idle, or connect it directly to vacuum and it should make the car run rough or want to stall. You can usually take it off and clean it if a chunk of carbon is holding it open.
For that matter there's also a good chance the passages are clogged and egr isn't working anyway.
 

53ryder

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So if I undo the hose connected to the egr valve and unbolt it and gently lift it up what will I see, if anything, underneath? Never played with an egr valve before so it's new territory for me. Educate me!


Glenn
 

Aspen500

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Never thought of the EGR valve. If it's stuck open or, as mentioned, a chunk of carbon is holding it open, there will be a rough idle. I guess to know for sure, you need to take it off and physically look at it. There's an open port and one with a pintle. Spray some brake or carb cleaner into the open port and it shouldn't leak out the pintle side (other than seepage that is). Usually though, it'll be obvious if it's open by looking at it. You'd also want to see if there's vacuum to it at idle (should not be). Easy way to check that is just unplug the hose with the engine idling. If it makes no change, the vacuum control is OK.

There is a gasket under the EGR valve but a lot of times it can just stay put and be reused. If it tears, then you need a new one OR a small amount of Ultra Copper RTV, if a new gasket is unavailable.
 

BudW

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The spark plugs, on our cars, only last about 30k miles (48k KM) on average. There is no sense putting expensive plugs in our cars because they will still need replacing and most likely, the more expensive plugs won't last that long anyway.

Other possibilities are:
- Spark plug wires not in correct order (1-8-4-3-6-5-7-2) – which is possible after new wire set installed.
- A new bad plug (doesn't happen often).
- Vacuum hose broke or popped off. The hose going to computer and hose going to rear bottom of air cleaner are common ones to be left loose.
If it started to do this just after the tune up, then these are the three most likely possibilities.
- The timing chain has plastic teeth on it – which are not known to last a long time. A loose timing chain is also a good possibility. To check it, remove the distributor cap so you can view the rotor. Get a 1-1/4” socket and breaker bar and put onto the crankshaft pulley. Rotate engine a short distance in either direction then stop. Then rotate the crankshaft in the other direction while looking at the rotor. The rotor should move instantly when crankshaft is moved. If it doesn't – then the timing chain is loose. A loose timing chain causes all kinds of problems.

There a lot of other things to check, but these are the most likely.
BudW
 

53ryder

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Have a breaker bar for a 1/2 drive, but no 1 1/4" socket. I've up to an 1". Will have to get a 1 1/4" one!

Glenn
 

AJ/FormS

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The single most common thing that happens, to cause rough running one day, is a tiny piece of dirt gets into the Idle air bleeds, and upsets the low-rpm/low-throttle opening, operation..
The easiest fix for this, is to remove the idle mixture screws and blow those two circuits out with compressed air. Two caveats; record your mixture screw setting prior to removing, and don't get carried away with air gun; some of that pressure will blow back into the float bowl. I suppose you could do damage in there but that would be a long-shot; just don't have your eyes anywhere near the IABs or the bowl-vent.

the first thing I would have done is the above, and
the second would have been to go hunting for a bad cylinder, and if I found just one, I would have replaced which ever part was causing it, namely; the plug or the wire, and inspecting the cap.
But the third thing, I would have done, NOT finding just one bad cylinder, now it's time to do all the other things already mentioned, in the thread.

But if you found a bad plug with a cracked or broken porcelain, this is ABNORMAL, and points to a detonation problem, and so warrants a deeper diagnostic. IMO, at this time, it's a bad idea to just replace the plug and to then keep on trucking.
 
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