diesel like idle

[gensic11]

i know there are tons of posts on rough idle but none seem to come to a conclusion. i am noticing that when i'm at idle i get some decent vibration throughout the whole truck it seems.. almost seems like it's not necessarily in the engine bay - rather more underneath the truck. i don't really feel it in the steering wheel or anything. when i hit the gas it smooths away perfectly and once i'm at idle it will take about 2-3 seconds before it calms down and starts to vibrate again.

i had the 00m12 fixed which fixed my RPM's dropping. my rpm's sit perfectly at 600-700 at idle and don't fluctuate at all when the vibration occurs, so it has to be something else.

any ideas on a quick fix? could it be my IAC not letting in enough air? does anyone else have any other ideas on what this could be? spark plugs/wires? sensors somewhere.. i'm sure it's only one thing causing the problem - just can't seem to pinpoint it using the "search" button.

thanks in advance for any help!

-G

 

[NHale623]

Remove the serpentine belt, start the truck and see if it's any different. Won't hurt anything to let it run for just a few minutes. The vibration may not be coming from your engine.

Check your motor mounts and transmission mount.

 

[KPT]

I was thinking transmission mount too. Does it make the vibration in neutral?

 

[Apu]

Mine does the exact same thing. It is more common in gear when it is loaded up then N or P. I think there is something with my exhaust, I m getting it looked at today.

 

[theultimategto]

I too have a 1997 XLT mine used to do this (diesel-like idle) when it was still under warranty, but they recalled it because of this problem, the dealer did everything, but i think it was somthing faulty in the cam, check to see if ur explorer went in for than recall.

 

[gensic11]

it's not as apparent in Neutral or Park yet i believe it still happens a little.

i had my cam chain tensioner replaced so i don't think it's that.. my engine doesn't vibrate.. it's just the same type of vibration that would occur when your truck looses rpm's - yet my truck doesn't lose RPM or try to die or anything.. it stays steady at 600 and doesn't sputter it just has some vibrations that are fairly loud. I do notice however that when my truck engine hasn't warmed up yet it doesn't do it.. once the engine warms up it starts vibrating more.. so i have a feeling the air (hot or cold) has something to do with my problem more than any mounts or anything.. the cold air seems to work better.. which is why i was thinking IAC?

let me know

thanks for the replies!

 

[Apu]

it's not as apparent in Neutral or Park yet i believe it still happens a little.

i had my cam chain tensioner replaced so i don't think it's that.. my engine doesn't vibrate.. it's just the same type of vibration that would occur when your truck looses rpm's - yet my truck doesn't lose RPM or try to die or anything.. it stays steady at 600 and doesn't sputter it just has some vibrations that are fairly loud. I do notice however that when my truck engine hasn't warmed up yet it doesn't do it.. once the engine warms up it starts vibrating more.. so i have a feeling the air (hot or cold) has something to do with my problem more than any mounts or anything.. the cold air seems to work better.. which is why i was thinking IAC?

let me know

thanks for the replies!

I replaced my IAC and it improved it, but it still does it on occasion. Mine is the EXACT same as you, it only occurs once it is warm. The vibration noise you are hearing is a resonation from the engine through the exhaust. I have pinpointed mine to the pipes between the muffler and the manifolds. The problem is I can't accurately figure out if it is an idle problem or an exhaust problem. If the computer keeps the idle around 650 in gear then it is a non issue and everything is perfectly smooth, but as soon as it dips down to around 600 or below it starts vibrating.

My mechanic didn't have time yesterday to check it out while it was on the hoist. I am going to put on new wires/PCV this morning and I am going on a 250 mile trip. I will let you know how it goes.

 

[slpdave]

I really don't have any experience with this but could it be a fouled plug or injector giving a bad fire on 1 cylinder?

Just an idea, maybe crazy, maybe not

 

[gensic11]

update.. it was a little over 40 degrees out today and i experienced no vibration at idle whatsoever.. i am almost positive now that air temperature has something to do with my idle - making me believe when it's freezing cold out the IAC doesnt' function properly.. anyone concur with this theory>

 

[Davek1]

what is an IAC

 

[ARTURPOLAND]

Is it a vibration or knocking sound + slight vibration. Did you change your oil filter recently. I did it once putting fiamm filter. JUNK !!! I had knocking valves noise and at idle it was exactly like old diesel. I changed the filter, oil (before change I added some kerosene to old oil so I flushed the engine). and the problem dissapear.

Archie

 

[maxerious]

mine makes a diesial like sound on idle to when its cold dont get much vibration but the sound is therre and it is Definetly more noticalble in the cold but it doenst seem to have any effect on performance/rpm it all but goes away when it warms up cant even notice it

 

[OZexplore]

when its playing up disconnect the IAC and see if that makes a difference if it is not working the idle will appear to become smooth

 

[Davek1]

what is the iac

 

[99SportX]

what is the iac

To finally answer your question, the IAC is the idle air control valve. It is electronically controlled by the PCM and regulates the flow of air into the engine at idle. If your engine starts idling like crap and dies, but runs once you give it some throttle it runs fine, it could very well be an IAC problem. My IAC howles like crazy, but only when it is really warm out (doesn't happen often lol). Still works fine though, in any temp.

 

[gensic11]

i have no knocking sounds or ticking or anything.. just the vibrations

 

[Apu]

OK, I have all but fixed the vibration. I still get a slight vibration in gear as the A/C compressor cycles, but it is barely noticeable. This is what I did on mine:

I set the parking brake and let it idle in gear. The vibration was coming from the driver side exhaust pipe coming off the manifold. There will be a catalytic converter on this pipe. I tapped the shield on the converter with a hammer and tightened up the heat shield a bit. Behind the converter you will see a couple of steel rods welded between the right and left pipes. I bent these rods slightly to help tighten them up and lower the resonation vibration between them.

I took off my throttle body and cleaned it. It was absolutely black on the inside. Use some throttle body cleaner and a Q-tip to get it all. Get a new IAC and replace as yours has enough miles on it that it could be replaced now. It is located under the cover that says SOHC and is really easy to get at.

Warm up your engine and shut it off and unplug the IAC. Start it up and set your base idle with the throttle screw at about 400 - 500 rpm (I used the tach on the dash please don't flame me!).

Do the TPS mod. Follow the instructions here. http://www.explorerforum.com/forums/showthread.php?t=79362&highlight=tps+mod

Hope this helps you!!