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I have a 2002 Cadillac deVille with 120k miles.
When the engine is warm, it bucks and surges during idle. It runs fine asl long as we are moving. But, when I stop at a light the engine will buck and stall.
This only happens when the engine is warm. It runs beautifully from cold start until the temperature gauge/graph is up about 1/3 of the way. It never overheats. the gauge/graph never goes above the halfway point.
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Remove the cap from the surge tank. Set the heater control temp to max (A/C in any mode EXCEPT max). Start the engine and idle until lower radiator to pump hose is hot. Allow the engine to cool to ambient, and then check/fill the surge tank and replace cap.
How many miles on it? I had to replace my engine at 220,000. When is the last time you had a tune up? Could be a couple of things. You might get more ideas on a Nissan forum.
I A C motor small part on throttle body ,controls idle mixture when they fail at idle the engine "hunts" for proper air/fuel mixture . when defective it causes o2 sensors and TPS to compete to set an idle thus the up n down effect.. auto wreckers if your broke new from your local parts store....dealer to much 1 plug in two bolts for most applications
i have a feeling the problem is not the sensors, they are reading lean indicates that air is getting into the engine around monitored system, basically a vacuum leak, which causes surging, also get a real time engine monitor not just a code scanner, some even have snapshot capabilities that will freeze the readings when something abnormal happens, just don't go replacing parts without knowing why
Try changing your PCV valve make sure the hose is clean and not full of oil. Also check the elbow end that goes to the intake they tend to collapse from oil saturation. Hope this helps.
I'd take a look at the temp sender...the engines computer may be
"thinking" the engine is still cold when it's not. That would cause it
run rich (and rough) after it's warmed up. Generally the sender can be
tested with an ordinary volt/ohmeter but you will need the
specifications available in most inexpensive manuals. As with any
complicated electronics system, I can only give you my best guess,
without the luxury of doing any hands-on testing myself.
Good Luck!!
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