Surging Idle

[samsonitesamsonite]

I know this problem has been beat to death but this question is a little different.

When I bought the truck 2 years back the previous owner (clamined to be an electrical engineer, but I am beginning to wonder) did a bad job wiring in a 96 OBDII 4.0 and computer into an 88 ranger... I have been fixing his problems and I have all but fixed the truck, now all that's left is the surging idle, the 96 harness calls for dual O2 sensors, but the 88 exhaust only had 1 bung, so he just hooked up the front O2 and let the pigtail for the second hang there. Could this cause the surging idle? I know Mike will most likley have a good answer on this one.

 

[Bob Ayers]

Does it do it cold and hot?

 

[samsonitesamsonite]

yep doesn't matter what the temp.

 

[Bob Ayers]

yep doesn't matter what the temp.

If it does it cold, then it's not the O2 sensors. The O2 sensors are only used in "closed loop". I suspect the IAC valve, or the TPS. While at idle, measure the signal lead on the TPS, it should be < 900mV.

 

[RobbieD]

Had a surging idle problem once in my B2; it was the fuel pressure regulator. Just another easy thing to check.

 

[steiner_5000]

I have a similar problem to figure out so I was wondering what an IAC is?

 

[Bob Ayers]

I have a similar problem to figure out so I was wondering what an IAC is?

Idle Air Control valve. Here is a picture of it (on a 3.0L), it will be located just behind the throttle body on a 4.0L:

 

[steiner_5000]

I really dont mean to steal this thread but this mite help. How do I test to see if the IAC is bad or maybe the TPS?

 

[samsonitesamsonite]

I replaced my IAC and TPS. It also idles a little 'rough at times'

another question that may or may not be related to this... would an exhaust leak, right after the cat, cause the engine to run poorly?

 

[MAKG]

After the cat? I doubt it. It might set a MIL for an OBD-II vehicle, since there is a downstream oxygen sensor. But that sensor will say that the cat isn't working (it's not used in managing the engine).

It will also cause rust and rather embarrassing noises, so you really do want to fix it.

 

[samsonitesamsonite]

Yes, I realize that. But remeber from post 1 in this thread that that O2 sensor is not hooked up. Im having a hell of a time with this. I hate working on other peoples screwed up projects, Next week I am just going to buy a first gen explorer parts rig, swap out the whole dash assemply and engine/tranny wiring harness, and screw this rednecked wiring setup.

 

[94 splash]

May sound stupid but maby u have a vacume leak?? i would pull off and check every hose because u mite have that one hose that a slit in it and u cant tell until u slip it completely off cause i had the same prob......

 

[samsonitesamsonite]

Doesn't sound stupid, but (I have all these parts on hand, so im not just "throwing parts at it") I replacled ALL the vacuum lines, lower and upper intake gaskets, TPS, and IAC

however, when I pull the vacuum line on the FPR nothing happens, well, other than a vacuum leak, the idle doesn't change much due to the FPR....

 

[ozzwoman9]

Does it change when you press the brakes? I've had break boosters cause vacuum probs before (on non ford related cars).

 

[robo]

try and clean the throttle body and check to see if therer is fuel in the vacuum hose to the pressure regulator.