Rough/Rolling/Stuttering Idle, 00 SOHC

[flogrown4995]

Hey all, so my SOHC has developed a very serious idle issue... Video here: My truck will normally not hold a steady idle when it's either cold outside, the truck was just started, or after running for more than an hour. The truck will not hold an idle really at all while I'm like sitting at a light or stop sign, or in traffic. It will only hold most of the time if I put the truck in Neutral while I wait. Not sure what can be causing this, I'm starting to believe it could be the IAC valve. I've heard things like the PCV tube toward the front of the engine cracking and breaking causing these symptoms. If anyone could help me, it would be really appreciated. I would love to get my truck running a lot better again so I can safely get to where I am going.

 

[J_C]

If the problem is a vac leak from the the PCV tube or elsewhere, you should see high long term fuel trims on an OBDII scan tool capable of showing live data.

If it is only happening at idle, I too would focus on the IAC and clean it out, then if that helps at all but the problem gets worse again, replace the IAC (or keep cleaning it again if enough time has passed that this doesn't become burdensome).

 

[flogrown4995]

If the problem is a vac leak from the the PCV tube or elsewhere, you should see high long term fuel trims on an OBDII scan tool capable of showing live data.

If it is only happening at idle, I too would focus on the IAC and clean it out, then if that helps at all but the problem gets worse again, replace the IAC (or keep cleaning it again if enough time has passed that this doesn't become burdensome).

I've seen a couple videos about the PCV tube, however I cannot find it in that same place its shown in the videos on my SOHC. Under where this guy shows is my heater core lines, not the big PCV elbow. Video referenced:

 

[swshawaii]

OP, your 2000 4.0L SOHC has a different PCV configuration and layout than 2001-03 two door Sports and 2001-05 Sport Tracs. If yours has a PCV elbow it won't be in the same location. Earlier SOHC engines are notorious for leaking intake gaskets. Scan for stored trouble codes regardless if you have a check engine light or not.

P0171 & P0174 4.0L SOHC's Sport/Sport Trac

 

[flogrown4995]

OP, your 2000 4.0L SOHC has a different PCV configuration and layout than 2001-03 two door Sports and 2001-05 Sport Tracs. If yours has a PCV elbow it won't be in the same location. Earlier SOHC engines are notorious for leaking intake gaskets. Scan for stored trouble codes regardless if you have a check engine light or not.

P0171 & P0174 4.0L SOHC's Sport/Sport Trac

So looking at that I have the PCV system he showed in the pics of Job 1. Could it be the tube that connects into the top of the intake cracked? Also do you have a guide to replacing an intake gasket? I'm not very skilled with cars so I'm not sure where its at/located on the intake of the motor.

 

[J_C]

^ It is possible the tube cracked, but I would not assume so yet. The older these vehicles get, the better it is not to tear into these hoses too much unless you need to, because you could have a perfectly intact tube but if you disturb it, that could cause a leak at a rubber grommet/gasket or break a tube.

I would sooner get an OBDII scan tool and see if the fuel trims are high. If they are not, it's unlikely to be a vac leak at the PCV intake or anywhere else.

 

[flogrown4995]

^ It is possible the tube cracked, but I would not assume so yet. The older these vehicles get, the better it is not to tear into these hoses too much unless you need to, because you could have a perfectly intact tube but if you disturb it, that could cause a leak at a rubber grommet/gasket or break a tube.

I would sooner get an OBDII scan tool and see if the fuel trims are high. If they are not, it's unlikely to be a vac leak at the PCV intake or anywhere else.

What would be considered a high fuel trim? I have a small little OBDII scanner that reads live data, so I'll try it out tomorrow.

 

[J_C]

^ Many say above 10 is too high, but 10 without an error code set is a correctable level and could be a sign you have some other problem in addition to a vac leak ("IF" any vac leak). As far as what fuel trim number is the threshold for exactly your symptoms with a vac leak being solely responsible? I don't know, don't remember the max fuel trim threshold # before the code is set. Odds are more likely it will be an extreme number or be within +10.

Do report any trouble codes set already.