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Rough Idle

chiefwhw

New Member
Joined
March 1, 2011
Messages
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City, State
Harlan, KY
Year, Model & Trim Level
2001 Sport Trac
Hey guys, Thanks for the site. Now my question.

I have a 2001 Sport Trac with 167,000 miles on the SOHC 4.0. I believe that it is a Job#2 Explorer. Build date is 9/00. I have a problem with a "loping idle" when in park or sitting at a red light or drive thru. Also, if I make a fast stop, the idle drops and the vehicle lurches. On cold start, the truck idles up to ~1000-1100 rpms. As it gets warm it drops to around 500. Then the idling issue begins. It starts loping and droping to 300 rpm or so and it sounds like there is a little monkey in the air cleaner box banging on a bongo drum 3 or four times as thumps are heard, then it goes back up. Seconds later, you it drops and the monkey is back. Doesn't seem to affect the driveability of the rig, runs pretty good, however, the fuel economy sucks and she does seem a little hesitant at times when pulling out from a stop. Transmissions seems to shift well (original tranny!). A few weeks ago, I had a CEL on and read the codes, there were two: P0171-System Too Lean, Bank 1 and P0442-EVAP Emmission Control System Leak (Small). I put some rubber treament on the fuel cap seal and placed it on the truck and now there is no CEL, but still have the rough idle. Used Lucas Fuel treatment with no luck. I did take the IAC off and clean it (a lot of carbon). Improved the hesitation some ,it seems, but still the rough idle. Checked the Air Filter and it is OK. Any suggestions would be greatly appreciated for this Fellow Exploder Owner...TIA
 



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Disconnect the IAC, does it do it worse, same or not at all?
Last Plug swap?
Last O2 swap?
Plug wires?
 






Last plug and wire swap was about a year ago. I unhooked the IAC and the vehicle quit. Would not start without it being hooked up. When I unhooked it, a large surge of vacuum (air) escaped from the IAC out the MAF hose. Does this mean there is no vacuum leak...? It is still doing the monkey now I hear a small high pitched whistle occasionally like it is sucking air. How do I test the IAC and the MAF with a Multimeter? Still no CEL on the truck. It works because It lights up when i start her up. ANy ideas on where to find a vacuum hose diagram for this truck. I am at my wits end on this thing...
 






Check the PCV valve and the associated tubing/hoses. If the front elbow is cracked it generally throws the P0171/P0174 together though. But with the extremely common problem this elbow causes it's worth a look. It will crack on the underside.

Re: IAC
From the FORD manual "Note: The IAC Valve Assembly is NOT ADJUSTABLE and CANNOT BE CLEANED"."The PCM uses the IAC valve assembly to control:

No touch start
Cold engine fast idle for rapid warm-up
Idle (corrects for engine load)
Stumble or stalling on deceleration (provides a dashpot function)
Over-temperature idle boost.
Air Assist to Injectors.

PCVelbow.jpg

KCV190PCVElbowHose.jpg
PCVElbowcrack.jpg
 






Could this also cause a stumble under acceleration? I was trying to speed up (from a stoplight) the other day and I noticed that my truck at 1/2-3/4 throttle stumbles for a few seconds.
 






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