How to: Diagnosing Rough Idle - Suspect: IAC Valve

[J. Anthony]

At idle and it started again.

I am real sure that you are so right. I was in the gas station getting some junk food for the night and when I got back in, the engine dropped RPM's, started to do the shimmy shake and I sputtered all the way home. I tapped on the IAC, nothing. When I unplugged it the RPM's did go up. Unplugged the MAF, no change. Tommorrow, plugs and wires!

Anthony

I thank you for the input. I'll let you know how it turns out.

 

[dogfriend]

I tapped on the IAC, nothing. When I unplugged it the RPM's did go up.

If the idle speed increased when you unplugged the IAC, then it may be sticking closed. You can take it off the intake manifold and look at the spool valve (the thing that moves back and forth to regulate the airflow). Look for any shiny areas that would indicate that it is rubbing on something. If so, either replace or try cleaning to free it up.

Its possible that you have a sticking IAC and bad plugs/plug wires.

 

[J. Anthony]

Parts on the way.

Good friend of mine, manager of O'Reilly's, has plugs and wires ordered. I will have them tommorrow afternoon. I think after 184,000 plus miles; I should expect to be making some parts changes; like MAF, IAC, Coolant temp switches, Crank Position Sensors and such. She knocks until she warms up, but brother she runs like a scalded dog when she gets on the highway. I still manage around 17 to 21 Mpg on the highway. My mpg went up when I started adding Lucas Oil to the Castrol I already used.

Thank you so much, Anthony

 

[gfisch]

Good friend of mine, manager of O'Reilly's, has plugs and wires ordered. I will have them tommorrow afternoon. I think after 184,000 plus miles; I should expect to be making some parts changes; like MAF, IAC, Coolant temp switches, Crank Position Sensors and such. She knocks until she warms up, but brother she runs like a scalded dog when she gets on the highway. I still manage around 17 to 21 Mpg on the highway. My mpg went up when I started adding Lucas Oil to the Castrol I already used.

Thank you so much, Anthony

Did you manage to get the problem fixed? Did it turn out to be plugs/wires?

I'm having similar issues. Have already cleaned the IACV and replaced the MAF w/ no effect on the fuel smell.

Thanks.

 

[scottb64]

If you unplug the IAC should the vehicle die? Mine does so I was wondering if this would indicate that I need to replace mine.

 

[ExplorerDMB]

it should die when you unplug the IAC. However, if you raise the RPMS up (around a 1000rpm) you can then unplug it and then bring the idle back down and it should stay running

-Drew

 

[dogfriend]

If you unplug the IAC should the vehicle die? Mine does so I was wondering if this would indicate that I need to replace mine.

It will either die or the idle will slow down if the IAC is working correctly. My truck did not die when I unplugged the IAC in this video:


http://homepage.mac.com/dogfriend/Explorer/iMovieTheater14.html

Apparently there was enough air moving past the throttle plate to keep it idling, although you can hear it slow down when unplugged.

My IAC was making the Woooo sound in the video, but was controlling the idle speed ok.

 

[scottb64]

What else should I check

It will either die or the idle will slow down if the IAC is working correctly. My truck did not die when I unplugged the IAC in this video:


http://homepage.mac.com/dogfriend/Explorer/iMovieTheater14.html

Apparently there was enough air moving past the throttle plate to keep it idling, although you can hear it slow down when unplugged.

My IAC was making the Woooo sound in the video, but was controlling the idle speed ok.

I have new plugs and wires and are installed correctly, the IAC appears to be working fine, and the MAF looks like it is in nice shape and clean and it is getting signal. The engine shakes at lower RPMs but when you give it a little throttle it smooths out. What else should I check? Fuel filter?

Has anyone heard of a procedure called Engine Vacuuming? I 'hear" that this will clean out the injectors and will improve performance. I had not heard of this until yesterday.

 

[pope_face]

Old thread, but I figured I'd check to see if the problem was sorted... if so, maybe someone else can use this info...

I think I may have had a similar problem in my truck... It was running rough, bogging under acceleration, not burning all the fuel, low idle, and black smoke coming out the pipes... One night, after leaving the truck parked in an underground parking lot while at the cinema, I couldn't get it started. I had gas leaking out of a couple vacuum ports, and when I removed the air intake hoses to the TB I had gas coming out of the TB as well... I thought it was the spark plugs/wires at first, but it turned out to be a bad fuel pressure regulator... I think it just wasn't returning the excess fuel to the tank, so my cylinders were flooding. I changed the spark plugs (which were completely black, apparently a tell-tale sign that you're running too rich) and it continued to do the same. I changed the FPR and managed to start the engine after cranking it for a bit (it wouldn't start before). It took a few minutes for the engine to smooth out and stop spewing smoke, and it ran rough for another half day, but now it runs perfectly... barely any vibration, no smell, clean exhaust, and quicker revs with more power throughout...

Now, I have a 4.0 OHV, but that might be the case with yours as well (if you have an FPR). Check the vacuum hose between the FPR and the manifold for gas... if it's there, it might be the problem.

 

[JerseyVics]

I can clearly see the shiny cylinder on our 99 V6 4.0L Explorer

but on the 04 V6 4.0L Epxlorer I can't seem to find it (I'm probably looking right at it)


can anyone post a diagram or a picture of the damn thing so I can diagnose the weird idle on my mom's truck?


thanks,
--Russ

 

[JerseyVics]

WTF?


just talked to a guy that works for a dealership and he's suggesting the reason I can't see an IAC valve is because my truck doesn't have it... apparently its drive by wire.


what else could be causing the truck to shake at idle (tach needle falls to about 500rpm)


already replaced the spark plugs and air filter.

--Russ

 

[dualhood93]

hi

so dont hit the motor with a hammer hit the acutal IAC with one. Dont hit to hard or u may damage the motor. They are none to fail if it does have a rough idle just dish out the money now then down the road.

 

[lakeranger]

rough idle and stalling problem need help?

I have a 2000 explorer 4.0 s.o.h.c. and when its cold it idles rough [500 rpm] and occaisionally stalls. I have tested the i.a.c. and cleaned the m.a.f. Also I cant get a signal from the diagnostic port. So no codes can be read. Any help would be appreciated.

 

[BrooklynBay]

Check the fuel pressure. You might have a clogged filter.

 

[rloftis]

Rough Idle!

If explorer is 4.0 sohc I would be willing to bet that the problem is the upper and lower intake manifold gaskets. The lower gaskets are made of silicon and sometimes become hard and brittle like plastic. This causes a vacuum leak that the IAC and MAF try to compensate for. I just did mine about 2 weeks ago and it runs and idles like a champ. Hope this helps!!

 

[CMOS]

If explorer is 4.0 sohc I would be willing to bet that the problem is the upper and lower intake manifold gaskets. The lower gaskets are made of silicon and sometimes become hard and brittle like plastic. This causes a vacuum leak that the IAC and MAF try to compensate for. I just did mine about 2 weeks ago and it runs and idles like a champ. Hope this helps!!

Would intake gasket leaks cause the idle to decrease or increase?



CMOS

 

[BrooklynBay]

Yes.

 

[CMOS]

Yes.

That answer is no help to anyone on this site.


CMOS

 

[BrooklynBay]

Would intake gasket leaks cause the idle to decrease or increase?
CMOS

You asked this question, and I gave an answer. For some reason you didn't like the answer. Maybe I should have been more specific. It will cause both problems, and sometimes feel like it's surging. So the answer is yes it will increase, and decrease the idle. Intake air is bypassing the engine controls causing an erratic malfunction.

 

[CMOS]

Much better. Thank you for elaborating.

CMOS