No idle/rough idle

[Trefty]

Hey all, just signed up to this site, looks like it's a pretty good place to get information.

Anyway, I'm getting a pretty rough idle on my Explorer(4.0 SOHC) and over the last week or so since it's got below freezing here every time I go to start it up after it's been sitting awhile, usually overnight, it won't idle at all and will die immediately. After a while it will idle on it's own but it's again really rough. I read some posts on here and it was suggested to tap the IAC with a hammer and I did that and it started to idle for me without having to keep my foot on the gas for 10 minutes or whatever. Do you think I should just change the IAC valve out for a new one? I'm guessing that that the valve inside might be getting some moisture in there and it's freezing causing it to sick closed? Would a new IAC fix this or could it be something else? To me it seems pretty likely that the IAC is to blame, but was wondering if anyone had any other ideas what it could be. Thanks alot:biggthump

 

[aldive]

It does indeed sound like the IAC is causing the problem.

You might try to clean it, however, a replacement is most likely the answer.

Good luck ...

 

[Trefty]

Yea I figure something must be sticking in there so I'll probably pull it off and see what she looks like. Quick question, when it's idling if I pull the connector of the IAC and the car stalls out, that should mean that the IAC itself is technically functioning?

 

[dogfriend]

Yea I figure something must be sticking in there so I'll probably pull it off and see what she looks like. Quick question, when it's idling if I pull the connector of the IAC and the car stalls out, that should mean that the IAC itself is technically functioning?

If its working, the idle speed will slow or possibly stall out. (My truck just slows down). However, it may stick intermittently - my first IAC would only stick after the engine was warmed up.

 

[Trefty]

If its working, the idle speed will slow or possibly stall out. (My truck just slows down). However, it may stick intermittently - my first IAC would only stick after the engine was warmed up.

Yea, once I get it to idle, it usually drops down to around 500-700 rpm and sometimes lower, feels like it's going to stall but hasn't done so yet. With the cold weather I'm having a hard time getting it to idle at start-up but I've got it to start the last couple times by giving it a whack so I'm sure somethings just sticking in there. I'm going to pull it off later and give it a clean.

 

[Trefty]

Ok so I cleaned out the IAC(it was fairly dirty) and the throttlebody(not too bad) and now it starts up fine everytime, idles smoothly for the first few minutes of driving and then goes back to a rough idle. Should I look at replacing the IAC vavle?

 

[dogfriend]

Is the idle speed too low when you have the truck warmed up? The idle speed should be 750 - 830 rpm with the truck in P or N, accessories off, engine warm.



Off topic: Hey, what happened to my original post in this thread?

 

[Trefty]

Is the idle speed too low when you have the truck warmed up? The idle speed should be 750 - 830 rpm with the truck in P or N, accessories off, engine warm.

When first started up it idles around 900 rpm. Sometimes it will stay in that range for the first few minutes of driving before dropping down but other times it will drop down to about 550-600 as soon as a I shift into R or D. The engine kind of sounds like a rolling rumble, I don't know how to explain that better, haha. I also notice a rattle when driving under load at around 2500 rpm but that's probably another issue.

 

[dogfriend]

The IAC should pull up the idle speed somewhat to account for the load when you shift into R or D. It might not be quite as fast of an idle as when in P, but it shouldn't feel like its going to die.

I'm also wondering now if you might have a vacuum leak - the SOHC are famous for having issues with the o-ring seals in the intake manifold. Its usually worse when the engine is cold. A vac leak may be the cause of the idle fluctuation.

 

[Trefty]

The IAC should pull up the idle speed somewhat to account for the load when you shift into R or D. It might not be quite as fast of an idle as when in P, but it shouldn't feel like its going to die.

Ok, so that should probably cancel the IAC out then as far as this problem goes.

I'm also wondering now if you might have a vacuum leak - the SOHC are famous for having issues with the o-ring seals in the intake manifold. Its usually worse when the engine is cold. A vac leak may be the cause of the idle fluctuation.

That's what I thought it was originally and I changed the seals on the lower manifold after hearing that it was a common problem on these engines. It seemed to take some of the hesitation away that I was having but the idle is still low. I'm wondering if checking the plug wires might be the next thing to try.

 

[Trefty]

I've heard that a faulty coolant temperature sensor could be a cause for a rough idle when warmed up, is this true? And if the sensor is faulty, would the temperature gauge on the dash still function properly?

 

[team]

might want to clean your MAF sensor also.

 

[Trefty]

might want to clean your MAF sensor also.

I've got some throttle body cleaner, would that be alright to use?

 

[dogfriend]

IIRC, there are two separate coolant temp sensors - one provides the signal to the gauge in the instrument panel - the other one provides the signal to the PCM. The second one is called ECT (engine coolant temp) and should have two wires, a VPWR and Signal Return. The gauge sensor only has one wire, the ground is through the engine.

If the ECT is bad, the fuel air ratio may be incorrect, especially when cold, so it could affect the idle.

 

[Trefty]

Ok, thanks for that dogfriend! So the ECT is located behind the thermostat housing correct? I talked to a mechanic and told him my problem and the first thing he said is to check the coolant level as if it's low it will affect the ECT and could cause problems. It's weird because before I cleaned the IAC I was having problems idling at startup but now it starts up great, idles nice and smooth for a few minutes then starts to get rough, I can feel it vibrating pretty good inside.

 

[dogfriend]

I think they are both in the vicinity of the thermostat housing, but the way to tell the difference is to look for the number of wires - you need the one with two wires.

 

[mudbug0426]

i need help! 4.0 idles horrible right after starting

hey guys im new to this site and so far it looks awesome, but i have a problem


i have a 96 explorer xlt 4x4 with a 4.0 ohv and it will not idle right.

it has 144,000 on it and the check engine light is on. i took it to autozone to have the codes pulled and there are two. p0174 and p0171. for each code they printed me a ticket saying what it means and the probable causes are.


ticket for p0171

definition - fuel trim bank one condition

explanation - the pcm uses the o2 sensor to calculate the air/fuel ratio of the engine. the computer has recognized a rich or lean condition on bank one only.

probable causes - 1. if bank one and two codes set together suspect fuel pressure or maf sensor.

2. o2 sensor defective

3. ignition misfire-repair

4. fuel injector problem



ticket for p0174


definition - fuel trim bank two

explanation - the ecm has detected a rich or lean air/fuel ratio condition on engine bank two.

probable causes - 1. if bank one and two codes are set together suspect a fuel condition or maf sensor fault.

2. failed H02S21

3. ignition misfire condition

4. fuel injector problem

5. engine mechanical condition



i have had this problem before but not to this extent. sometimes when i would start it 'cold or hot' it would idle a little rough for a few secs and be fine. since the check engine light first came on which has been almost if not a month now with these two codes, i have replaced the maf sensor, idle air control valve, the two o2 sensors before the cats, new spark plugs and wires, the upper intake manifold gasket 'the one that sits between the top of the manifold and the fuel rail'. im out of ideas now, im thinking and hoping its not a fuel pressure problem, when replacing the gasket i did take out the injectors one by one to make sure nothing was blocking the screen on the tips.


after replacing the maf sensor, thats when it started to and now will idle horrible for roughly 20 to 30 seconds, then it will idle up to about 1100 to 1200 for a few secs and come back down to 1000 rpms and will idle fine until the next time i start it, and it will do the same thing all over again every time.

i have also checked for broken vaccume lines and they all look intact.

any ideas??

 

[mikepier]

I think they are both in the vicinity of the thermostat housing, but the way to tell the difference is to look for the number of wires - you need the one with two wires.

I have the "vibrating" idle also. I thought it might be the ECT. I tried to disconnect the harness and see how the truck would run, but the truck did not want to even start, so i connected it back. I have no CEL on. I was going to pass by Auto Zone and see if they can pull any codes. Would they still be able to find faults with no CEL? Would it indicate the coolant temp reading?

 

[dogfriend]

If you have a scan tool that can read Ford PIDs (parameter id) then you should be able to read the coolant temp from the ECT sensor. The readings will either be in DC volts (.4 - 1) or in Deg F (200 - 160). IDK if the scan tool that Autozone has will do this.

Also, it is possible to have stored and/or pending codes without a CEL.