Rough Idle when truck is warm and parked for short duration 30-60minutes

[snowmann]

As the title states, if the truck is warmed up - say a cross town commute, then parked for a short period - under an hour... the truck starts fine, but then has some nasty hesitiation/rough idle and sometimes kills... If I keep my foot into it it "cleans out" and runs normal... (This usually only lasts 30 seconds or so... then the car is completely driveable with zero issues)

If the truck is cold - it starts/idles fine

It has grown from a once in a great while issue... (less than once a month a year ago...) to an everytime the fore mentioned variables are in place...

No check engine light - no codes...

no obvious vac leaks...

Any ideas?

 

[Nhaz]

moar info!

year model milage and whereasbouts

 

[sholzy]

Mines been doing the exact same thing for about 4 months. It started about a month after I replaced the MAF sensor. It's almost like having a choke on a carb slightly closed so it's running slightly rough. I cleaned the IAC valve and it helped a little. I suspect the IAC, but I don't have $80 to throw at it (especially since I'm starting to have tranny problems).

 

[snowmann]

96 4.0 w/ 170,000 miles

Ambient temp doesn't matter... Recent tune up parts replaced... But was doing before and after...

 

[snowmann]

Update:

Cleaned the air filter, replaced the PCV, cleaned the TB and the IAC valve... now the truck won't come out of the idle issue...

The Advance down the street has a IACV for $35... gonna try that... Wondering if I did the IAC in by loosening up some of the crap...

 

[snowmann]

2nd update


Replaced the IAC, same issues... just runs horrible for first couple of seconds and then clears out... idles like its flooded or missing badly...

I'm lost...

 

[jhammel85]

My truck does the same thing...I'm just as stumped..

 

[Nhaz]

The IAC is a really simple design and not easy to hurt. It either works or it doesn't , it really doesn't have much in between.

When is the last time you replaced the plugs/wires?

 

[legoms013]

96 4.0 w/ 170,000 miles

Ambient temp doesn't matter... Recent tune up parts replaced... But was doing before and after...

The IAC is a really simple design and not easy to hurt. It either works or it doesn't , it really doesn't have much in between.

When is the last time you replaced the plugs/wires?

He probably replaced them then.


I'm curious to the solution to your problem, my 96 mazda b4000 does the exact same thing, albeit alot less often.

 

[snowmann]

Plugs/wires are a little less than 2 years old...

Motorcraft original parts on those...


Yesterday thru the day I messed around more... The problem had developed this week into the point where if I didnt keep my foot in it it would die... Previous to that it would work itself out if/when it occured... (Which like I said was once in a great moon...) I did snug up the lower intake bolts and got the problem to receed slightly to the point where the truck didnt completely want to fall on its face... it now will idle by itself but still is not smooth... I'm thinking it may be worth a lower intake set...

I can repeat the symptoms if I warm the truck, let sit for ~30-60 minutes and restart... Oddly, If you warm, then restart before ~30 minutes it starts fine... depending on how close you are to that ~30 minutes it gets worse and worse... and if longer than ~60minutes it starts like a champ again (truck has cooled at that point)

In another thread I bumped up, a poster suggested a coolant temp sensor - Seems logical, as its odd that works fine when warm, or normal driving, but in that initial 30 seconds seems like its flooded or something...

I may just throw a coolant temp sensor on as well, cheap insurance...

Another poster suggested an unequal expansion that drives a gap under a certain temperature range and/or a sealing condition... I believe both the intake and heads iron? shouldn't be getting any drastic expansion differences as if it were aluminum and steel or plastic and steel? Who knows, I've seen stranger on cars...

I have done everything independantly and then tested as well, seems this is a common problem baffeling quite a few people, So hopefully I can share that one oddball thing that curbs this issue...

 

[kimcrwbr1]

You can allways check the resistance on your plug wires sand and tighten the coil ground, replace any hard vacuum lines. I think the key is to test it whenever you do something, if you do a bunch of stuff at the same time you wont know what was wrong for future referance. Let us know if you figure it out.

 

[sholzy]

In another thread I bumped up, a poster suggested a coolant temp sensor - Seems logical, as its odd that works fine when warm, or normal driving, but in that initial 30 seconds seems like its flooded or something...

I may just throw a coolant temp sensor on as well, cheap insurance...

I replaced my coolant temp sensor a few months ago trying to figure it out but it didn't help any. The only thing that has helped is the cooler morning air temps.

Would a defective air cleaner temp sensor cause these symptoms?

 

[Warren 86 ranger]

have you tried the egr mine was bad and i had he same pro change it out see if it helps it cleared mine up big time

 

[snowmann]

I pre-penetrating oiled the bolts at the EGR in the event that I need to take that off...

Is there anyway to test the EGR?

I dont have any access to high dollar genesis scan tools or anything...

I did have a couple of rotted vac hoses from the EGR to the manifold I believe that tripped the CEL...Replaced those about a month ago...

Wouldn't a faulty EGR pull a CEL?