Emissions system problem?!??

[kwheat4136]

I recently bought 2000 Ranger XLT 2.5L 4 CYL 5 speed manual. 145700 miles.

Runs great most of the time. I've discovered that when it is idling at startup (the usual higher RPM), if I quickly rev it to bring the idle down it becomes very rough running (almost like it's too rich) and won't stay running, especially at stops. Almost like something is sticking open/closed. I have to keep my foot on the accelerator so it won't die. if it does die in this situation, is very hard to start. Seems to be worse if the AC is on, but not certain on this.

On the contrary, if I don't quickly rev the engine during idling, it runs great all day, very smooth and does not die at stops.

mileage seems fine, no smoking, no fluid leaks, no overheating, all fluid levels have remained constant....

This is what I've done so far:
spark plugs/wires replaced
oil and filter changed
fuel filter replaced
added "seafoam" to fuel tank
IAC valve replaced
MAF sensor replaced
DPFE sensor and hoses replaced
EGR valve replaced
PCV valve replaced

Could this be an O2 sensor problem? It is unclear if any of these things have ever been replaced. (limited service records by seller).

Thank you!

 

[Mark_88]

Howdy and welcome to TRS~!

First thing I would check that I did not see in your list is codes. If there are no codes then it makes it a hit and miss diagnosis/fix which are the toughest to deal with and often leads to part replacement that may not be needed.

There is a warm up routine that is normal and should not be dependent on the urge or attempt to lower the idle prematurely. Other than running the engine at a higher idle manually it is not possible to speed this process up.

But a defect in that system could indicate a possible issue with the PCM or ECM (computer) if anything. The computer controls the idle based on sensor feedback particularly from the coolant temps sensor.

I had a really rough idle on my 96 2.5 (implant from 98) because the DPFE had loose hoses and they would actually fly off and cause it to have hard starting issues and a loud putt putt putt noise that scared the carp out of me.

You can try cleaning the contacts on the Temp Sensor and Temp Sending units that should be located right at the front passenger side of the engine. See if that helps clear it up because it could just be a wonky connection that is triggered spontaneously and sporadically.

 

[kwheat4136]

thank you for your quick reply! I'm not sure if any codes are involved but the CEL is not coming on. I'll check on your suggestions! thanks again!