The surging usually comes from the IAC hunting to maintain a stable idle. usually your symtoms occur from a vacuum leak of some sort. plastic intakes are sometime found to be cracked from heat embrittlement. spray the top of the engine with brake clean when running. if the idle changes when spraying in a certain area you are locating the vacuum leak. the idle will change when the engine sucks in the brake cleaner.
SOURCE: I changed EGR valves, selinoid, sensors, and even
go to auto zone or someone with a scan tool to find out what codes are stored on the computer in the car
SOURCE: 1997 ford thunderbird 4.6 keeps coming up with
U don't say codes but most likely the sensor codes are just responding to a problem in the engine, mainly and most common is a lean fuel/air mixture, this is most often caused by vacuum leaks, it only takes a small leak to set the lean codes for the O2's and turn the check engine light on, I am a 25 Year Ford dealer tech and this is the common cause of O2 fault codes, to check for vacuum leaks get a bottle of propane and attach a piece of rubber hose to the end, spray propane around the top of the engine, work slowly and hit all vacuum hoses and the top and edges of the intake manifold, if u hit a leak you will hear the engine change tone most times or increase in rpm slightly, then look closely for the leak, it can be leaking intake gaskets or a cracked rubber vacuum line, even a leaking Vacuum brake booster can set these codes, if u don't find anything obvious it is time to have the dealer hook up there scanners and look at what is going on in the fuel system to create the O2 codes, don't hang anymore parts on, u have already wasted about $100 I would guess.
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