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Hey guys.. does it normally happen like early in the morning or late at night when u start the engine? In other words, does it happen when your engine is cold? b/c I have this same problem right now too, and I asked my mechanic uncle, and he told me that it is the idle control valve or switch or something. I forgot, but he told me it is simple to fix. I asked him if it is a big problem and he told me it isn't but that I should get it fixed. Hope this helps.
 

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I had that problem with my 91 sedan.... I think it was air in the cooling system, which in combination with many other symptoms, all related to a big HG repair. However I think the fluctuating idle could also be caused by something like a bum sensor or something like that...
 

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The most common cause for this variability is when air is in the cooling system which allows the temperature sensor for the idle control valve to be alternately exposed to liquid then air. The sensor controls the idle speed depending on the temp. it sense. It gets mixed signals when air contaminates the cooling system and tries to step up the idle, then down, then up, etc. Fix the leak in your cooling system and bleed the air out and the erratic idle will likely be gone..
 

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bigdad said:
The most common cause for this variability is when air is in the cooling system which allows the temperature sensor for the idle control valve to be alternately exposed to liquid then air. The sensor controls the idle speed depending on the temp. it sense. It gets mixed signals when air contaminates the cooling system and tries to step up the idle, then down, then up, etc. Fix the leak in your cooling system and bleed the air out and the erratic idle will likely be gone..
I may be wrong but what you indicated is normally associated with engines with the fan attached to the waterpump. A potential leak would cause the temp sensor to raise the idle to cool the engine and lower the idle after the temp drops. Ours use electrical fans and the idle flux is minimal when the fan is on.

I was told our cars are very sensitive to carbon buildup and must be cleaned often. This includes the throttle body and even the spark plugs must be inspected or cleaned if the problem persist. Some 91 Legends were recalled (mine was fixed in 95') for this problem. They replaced the entire throttle body. Top engine cleaning or fuel injection cleanings are also recommended if the problem continues. Unfortunately, this is an annoying problem with many variables.

PS Someone also mentioned changing the PCV vale fixed this problem.
 

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I said a common cause for idle variability is air in the cooling system...it is not the only one. These cars have an idle control valve that bypasses incoming air in the intake manifold and the temperature control sensor has input to this valve, and thus can affect the idle....
What is also true is that Legends have notoriously bad radiators (plastic tanks) that often develop stress cracks around the mounting flanges and throttle cable clip. This minute cracks may not leak very much coolant (although some do!) but when the system cools it draws in air into the supposedly sealed system (instead of coolant from the reservoir bottle). This is how air can get into your system. Carefully inspect the area around the radiator, fan shrouds and the like. Any evidence of green/red coolant stain or moisture will give it away. Low coolant level in reservoir or radiator is an indicator of leak too. There is a bleeder mounted to the top radiator hose connector to the block. Loosening this 12mm while the engine is hot and the heater is running will allow air to escape (careful, it will sputter and squirt out hot coolant when you do this). Do this bleed several times over a few minutes (to allow air to collect at the high spot) until solid stream comes out...then your air should be out of the system. If you do have a leak and haven't found it or repaired it, the air will return over time.
 

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Gotta love those plastic radiators, eh?!
 

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it is funny that some times it will fluctuate and sometimes it wont... wat do u think can cause this!!!! and what can i do to fix this

thanks
richard
 

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From what I remember of this being discussed on the other boards it is either as simple as readjusting the Idle control, or as difficult as replacing an O2 sensor...
 

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Yea, I had this happen several times on my Legend with 299K.
The idle was jumping up and down.

Did not know what caused it - was very concerned but did not do anything about it

It disappeared and I have not experienced it for about 50-60K now.

Go figure??
 
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