Random rough idle, random perfectly smooth idle, no engine code. Please help!

[boomouse]

I have been exactly the same problems you have from a '97 X Limited imported from the Japan used car market (into Manila via Subic Bay).

The idling would go from near racing at 1500 rpm down to a marginal shudder that would barely hold up. When cold, the engine would start but promptly die if I stay off the gas.

On a hot day (and we've got lots of those), standing in traffic, idling would slowly grind down to a stall.

I have the entire intake system cleaned short of replacing the IAC and the idling seemed to stabilize a bit in the sense that there was less stalling but the 4.0 OHV motor would still keep on hunting and this time cycling the A/C compressor too.

The last one had me checking the freon lines for leaks and checking the pressure for correct refrigerant loading. I found a leak in the cooling coil area, a plugged up expansion valve, and a small hole in the accumulator. I changed the coil, accumulator, and expansion valve and voila!

The darn thing is now a docile as a lamb. A/C doesn't cycle, idle does not hunt, it stays put at just under 1,000 rpm and maintains this even when the AT is left in drive while standing or set in neutral.

I don't know how much of A/C you use (no mention in your post) but it is indispensable in Manila and doing maintenance work on the A/C did the trick.

Sure, the parts were not cheap but I'm happy.

 

[Blind]

I use the A/C all the time and it works perfectly, I would think if it was leaking it wouldn't be blowing cold.


I swapped the IAC with another one today, we'll see how that goes.




btw, I did a bunch of search's here and was unable to find any mention of testing the DPFE without a scan tool. The only test was if the voltage going into it was 5 volt's to show the wire to the ECU was good, I tested that and it was 5 volts but that is not actually testing the sensor.

 

[aldive]

http://www.explorerforum.com/forums/showthread.php?t=164517&highlight=DPFE

 

[Blind]

yes that is the thread I found, and like I said there's no mention of testing without a scan tool.

 

[Diddy74]

I would definetly look into the DPFE replaced mine along with the EGR and its running smooth, I had P303 and P402 misfire cylinder 3, and exsessive exhast gas flow. I dont know if it could cause a "random" misfire, but it helped smooth out the idle and accel.

 

[Blind]

replaced the DPFE today, no difference.

I think the crank position sensor is next

Does this truck use a cam position sensor? I read conflicting info at autozone.com in their repair guide info.

thank god my buddy works at napa so I can keep exchanging these parts that make no difference...

when I reset the codes before driving with the new DPFE on it, a new one came up, the list this time was:

0420 - catelyst system not working right
0300 - random/multiple cylinder misfire
1151 - O2 sensor bank1 missing or indicates lean

I believe that the 0420, and 1151 codes are symptoms and not causes, so I will ignore them until the 0300 and rough idling is fixed.

 

[shabookie02]

I have the same exact issue with my 03 mounty I am going nuts to find the issue I just raised the idle on my tb to 900rpms it seems to help. I have checked for vacuum leaks found none have you heard anything yet????

 

[Bobmbx]

This sounds like faulty fuel injectors or a fuel control system that forgets what its supposed to do.

When you're at idle and its acting up, start pulling plug wires one at a time. If the engine gets worse, re-connect and move to the next cylinder. If you pull one off and nothing changes, thats your guy. At the least this will identity the issue to a specific cylinder(s). Remember, do all the cylinders. It could be more than one.