Rough idle question help (1 Viewer)

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Recently did a tune up on 97 Lc with 235k. New dist cap and rotor, factory Toyota plugs and air filter. At idle, in neutral or park, the idle has a periodic rough grumble for a sec or two, returns to smooth idle and keeps repeating. i checked for vacuum leaks and didn’t see anything, checked timing as well, @ 3 degrees. Any suggestions? Was thinking about wires and coil just for peace of mind, as I acquired this car recently and doing some deferred items. From the receipts it looks like the plug wires were replaced in 2008 but only 40k miles ago, no history on the coil. Wires were replaced with OEM, assuming the mechanic replaced them, as they are the factory original manufacturer. Any diagnostic tests I can do before buying parts?
 
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if their factory wires there is a date printed on them, that should give you an idea of about when the wires were replaced. do you have a check engine light on? do you have any sort of history on the truck?
 
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Good point, I’ll check the date of manufacture. No CEL and limited history of vehicle. If the wires are from 2008, do you think age or miles is a larger concern?
 

baldilocks

Battle Ground, WA
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Plenty of original wires lasted 15 years or more. A simple thing to do is to remove those two plastic covers over the plug wires on top of the valve cover and run the engine at night while looking for electrical arcing escaping the wires.

Did you notice oil down in the spark plug tubes? This is the most common cause of misfire per the FSM.

Did you get the plug wires snapped onto the plugs well enough. There have been new plugs that are faulty also. This is uncommon but does happen.
 
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Interesting regarding the oil. I did notice some of the plugs were oily, luckily I took a pic. Looks like one was really oily but the others look reasonable. So clean out the spark plug boot with electrical cleaner and maybe wipe the plug galley to remove as much oil as possible. I definitely didn’t see any really wet oil, so I don’t think there’s a valve cover leak, at least not too bad. Any suggestions on how to clean?

EF121B22-A248-4DC9-92D8-DB0EBF6473AF.jpeg
 

baldilocks

Battle Ground, WA
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Oil in the tubes indicates leaking tube seals which are fit onto the valve cover. There should never be oil in the tubes.
 
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#6 tube seal is shot if your plugs are in order in that pic.

So valve cover, spark plug tube seals, throttle body gasket, and PCV valve grommet are in your near future. May as well do the PCV valve and both valve cover hoses at the same time.
 
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Replaced with Toyota factory plugs, so yes got the right ones. I guess I got some more parts to order! Will report back once completed. Appreciate all the comments and support.
 

baldilocks

Battle Ground, WA
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As a point of reference; when I bough my 80 five years ago it ran extremely smooth and with nary a miss. Last fall I had the plenum off so I decided to go ahead and replace the plugs and Bosch wires that came on it with the oem plugs and nearly new oem wire set that resided on my spare engine.

The plugs that came out of the engine in my cruiser were NGK G power platinum with the pointed electrode similar to but not as fine as the point on those iridium plugs pictured above. Off to the store I went to pick up six of these same NGK’s. My spare engine, when it was in use in my last rig, never ran as smoothly as my current engine with more miles and Bosch wires.

As it is now with oem wires and the G power plugs she runs very well but the random misses, which no engine is totally free of, are more frequent than before running the same plug with Bosch wires combo. I believe in oem parts but my experience shows that oem plugs and wires are not required and maybe not even the best choice.
 

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