I just bought a 1998 ranger 4x4 4.0 automatic that runs well except for a 2000 rpm idle. Code reader says the TPS is bad, which I replaced. No difference. Any other owners with same problem, before I start throwing money at it? Thanks
The idle control valve, also commonly referred to as the idle air control valve, is an engine management component that is found in one form or another on the majority of road going vehicles. Its purpose is to control and...
If there is indeed an issue with the iac valve and it was causing the engine to idle so low that the engine was barely idling/stalling,
the previous owner may have adjusted the idle set screw too far inward trying to increase idle enough to keep the engine running & when he did,the throttle body shaft (that the throttle blade is screwed to) may have moved the tps ratchet mechanism too far in one direction,which could have also moved the closed throttle voltage out of range enough to trip the tps code.IOW- anytime you open or close the throttle blade (via the set screw or by doing so manually or with the gas pedal) it changes the position of the tps mechanism and this movement alters tps voltage.Youre good as long as the tps closed throttle voltage stays in range.I believe its .50-1.19 volts on a Ford tps.The tps doesn't have to be set to a specific value either,when you adjust it.It just has to remain within this range.
A quick test for the iac valve is to locate & disconnect the harness from the valve and listen for the engine to either idle down or stall completely, especially during a cold start when the ECU opens the iac fully.If the engine doesn't idle down or stall at cold start,once the iac harness is disconnected, that indicates the iac is stuck open or not working
or the idle set screw on the throttle body is adjusted too far inwards (which increases idle) & the ECU has lost control of the idle with the use of the iac valve.Base/mechanical idle should be set between 550-650rpm (harness disconnected) so that the ECU can take over from that point on up (650+ rpm) The ECU can use the iac to increase idle above the value you set with the screw,but it cannot decrease it below the upper value (650rpm) you set it to,so you must keep the base idle value within this range and not set it above the 650rpm value,if you want the ECU to control it correctly.Make sure you clear the tps code out also so that youll know its a new code/fault if the same tps code reappears.
Vacuum leaks & a stuck open purge valve can also cause a high idle.On vehicles with a maf sensor,any air that enters the engine that has not been metered already by the maf sensor is seen as unmetered air by the ECU and it will create a vacuum leak.A vacuum leak creates a lean condition which then triggers the ECU to richen the fuel mixture in an attempt to compensate for the unmetered air.So a leak will definitely cause afr and idle issues.People use different methods of locating leaks so I wont advise which method you should use,but I prefer a handheld propane torch with a ft or two of vacuum hose attached that I can run alongside hoses, fittings,gaskets,etc,etc.A fire extinguisher should always be handy when using any flammable substance to do this.Ive also heard of people using carb cleaner, water,oil or a smoke machine to find leaks.Once you pass over a leak point with propane, with the engine running, the engine idle will surge upwards.