Howdy , new guy here, I purchased an '04 Ranger (4.0, 5 speed, 145k miles, 4wd) about a year ago and recently it started revving after starting, it would jump to 1500 rpms and slowly idle down but now its worse sometimes to 2000 and stays there, I disconnected the battery a couple times and that seems to help for awhile then acts up again, if there's an easy fix i'd like to try it before going to a garage, thanks in advance, Tim

 

Welcome to the forum

Reads like you may have a vacuum leak
You have a 4.0l SOHC engine in a 2004 Ranger
PCV Valve hose was a common leak point, has two elbows that can crack and allow air to be sucked in

Cold, and even warm, fuel injected engine should REV on start up, 1,500 is OK, 2,000 is too high

After engine is warmed up, let it idle and unplug the 2 wire connector on IAC Valve, idle should drop to 500rpms or engine may even stall, thats good it means no air/vacuum leak
If idle doesn't drop then there IS a leak

 

That sounds like some good info ! will check it out and respond, thanks much , Tim

 

So I'm old school Y block / small block, when I pop the hood on this Ranger l'm lost so took it to the local garage with the hi idle issue,, they replaced the IAC and cleaned the throttle body, $329.00 later it still revs,, start it up revs to 2,000 then 1,500, eventually to normal while sitting, but when I start driving it never dips below 1,500 until I come to a complete stop then goes to normal,, seems to know when I'm moving ,, help !

 

Yes, it won't drop RPMs until speedometer is under 5mph, that's an emission requirement

But still too high for warmed up engine, should be 1,100rpms then drop to 750 under 5MPH, in neutral

 

Thanks for the reply, emissions requirement ? RPMs don't drop until under 5 mph ? that's rediculous and not helping gas mileage, I like the 4.0 but not all the crap attached to it, seems like unnecessary wear and tear..

 

Idle RPMs, under 1,000rpm, has to be a Richer mix or engine will overheat, so not really an MPG issue between 750RPM idle and 1,100RPMS with No Load, i.e. coasting
Its why older idling engines often failed emissions test, Richer mix caused higher CO and hydrocarbons

Not sure how "wear and tear" would come in if RPMs are under 1,500 with No Load
A running engine is a running engine

And its why we have "auto stop/start" now on any newer vehicle, to pass "idle emissions" tests


If you have a manual transmission(or automatic) with fuel injection never coast in Neutral going downhill
In the old days with Carbs it was common practice to shift to Neutral and coast downhill to save fuel, but its opposite with fuel injection

Fuel injectors can be SHUT OFF by the computer, and they are when coasting IN GEAR
As long as RPMs are above 1,500rpms and your foot is off the gas pedal, computer will shut off the fuel injectors while coasting, it will open a few now and then to keep Cats Hot, but otherwise 0 fuel consumption
Bonus, engine braking also saves "wear and tear" on the brake pads/shoes :)