Intermittent rough idle on warm start....

[Rupert8]

Hi again,

I have a 92 4.0L Eddie Bauer Explorer.

It starts from cold just fine. Every time.

However, when it is started after it has been driven and the engine has heated up it sometimes (maybe 1/3 of the time) idles rough as anything and feels like it is going to stall. It doesn't do this every time and only after the engine has cooled for half an hour or so.... If I start it after a few minutes of not running, it is fine.

When it idles rough, it will drive very 'jerkily' (ie if I am backing out of a parking spot) when I put it in gear. When I give it some gas and increase the RPMs, it somehow clears and drives fine (although it feels a little underpowered, but this could just be me...).

I have changed the spark plugs, air filter, fuel filter, oil.... I can't detect any leaks on vacuum hoses.

Does this vehicle have an EGR valve? I can't find it if it does.

Someone suggested an idle air control valve - could anyone back this up (I will probably give it a go anyway but it feels like I am just throwing money at this now).

Any ideas here? It is slowly getting worse.... Has anyone had a similar problem?

Thanks in advance for any help - I need to get this fixed...

 

[arco777]

I have the same issue from time to time. Fix is always to put it in gear and drive away, and it sorts itself out as soon as I get moving. For me the problem has not gotten worse in several years. Never have figured out what it is but you're not alone.

1992 shouldn't have an EGR valve (maybe Cali emissions does?). Typically late 93s and 94s have EGR valves. You'd see it attached at the driver's side of the intake manifold if it did.

 

[FR-425]

Same intermittent problem here. Solved.

Although mine was never as severe as yours.

Here goes:

Intermittent connection at the Throttle position sensor. Yep simple.

Disconnect, clean with electronics cleaner.

Give the connections a dab of "Dielectric silicon" (light bulb grease)

Done!

 

[FR-425]

This issue never did throw a CEL,, Weird.

You'd think it would throw a high-low voltage at TPS or something.

But the clean job did the trick.

So like the **** retentive cracker head that I am, I repeated this clean and grease on every connector on the truck.

Not one electrical gremlin since.

I was forced to do this on a Toyota that had been play'n in the salt water!

Beach wheel'n = BAD

 

[Rupert8]

Thanks for the input, all. I will take a look at the TPS tomorrow and check back in with the results...

 

[littlebro294]

can you post if it helps? my 1994 X sport has been doing the same thing, but it has been feeling underpowered constantly. If it works for you i'd like to know so i can see if it helps mine

 

[FR-425]

MotorCraft TPS is only $52

If you suspect it replace it.

Gas mileage alone is reason enough.

Keep the "sort-of working" one as an emergency spare.

Another note on rough idle after warm:

probably need one of these too: It's the temp sensor for the PCM

The one "near" The housing for the PCM looks like this.

It is a bad Temp sensor.

http://www.rockauto.com/catalog/moreinfo.php?pk=951148&cc=1119631

Been here, done that already on the 94.

There are (2) sensors, so make sure you change the one that has a cone on the end of it, next to the thermostat housing.

 

[damarble]

Mine has been doing that forever. It usually went away if I gave it some gas so I just dealt with it. Good to know.

 

[Rupert8]

Hi,

It took a while to get to due to some family events but I just changed out the TPS. No change: the explorer is still idling rough after cooling for twenty minutes or so. I'm stumped here.... Anyone have any further thoughts?

Both coolant temp sensors have been replaced.

Many thanks!

 

[arco777]

Cleaning the fuel injectors is the current suggested fix. Removing them and soaking them in fuel injector cleaner seems to do the trick, it's recommended to change the filter in each injector at the same time.

 

[murkinstock]

You can try to unplug your IAC. See if it runs better without it. Mine was going bad and it would do sort of what you explained so I just disconnected it until I could get a new one (I drove with it unplugged for over a month) It might idle a little low though. Other than that I never really had a problem without it. I got a new one and now it starts fantastic every time! Worth a shot. Good luck!

 

[Rupert8]

Hi, thanks for the replies. The IAC has been replaced with no improvement.

Removing and cleaning fuel injectors seems like a tough project. I'm not sure I have the wherewithal for that job. Would a gas-tank injector cleaning product work?

Again, all input is appreciated on this as the problem seems to be slowly getting worse....

 

[murkinstock]

Hmm. Have you tested the fuel pressure? Maybe your pump or FPR is going bad. If you want you can try injector cleaner. It wouldn't hurt at all. Except just a few more bucks into it. Make sure you do a fuel pressure test and that it's low PSI or something before replacing the pump or FPR though. I'm more just throwing ideas your way. Yeah because when I was having the problems I also replaced my fuel pump and FPR about the same time I did my IAC. (All my fuel would leak back into the tank in about 10 minutes of not running and I would have to prime it about 3 times before it would start. Still needed a new IAC though. If I revved the engine it would hold it for a very long time.)

To check the Fuel Pressure Regulator start the engine and run it for a minute, then shut it off and pull the vacuum line off of it and see if there is gas in the vacuum line. If so then it's bad.

Now I'm just throwing possible ideas. Just take them into as a possible direction but don't jump right in and replace parts. I don't want you wasting money because of me lol. Good luck man!

 

[arco777]

Hi, thanks for the replies. The IAC has been replaced with no improvement.

Removing and cleaning fuel injectors seems like a tough project. I'm not sure I have the wherewithal for that job. Would a gas-tank injector cleaning product work?

Again, all input is appreciated on this as the problem seems to be slowly getting worse....

Member RustySJohnson swears this is the fix for this exact problem. Check out this thread - http://www.explorerforum.com/forums/showthread.php?p=3248660

Cleaning the injectors is actually pretty easy. You simply remove the upper intake manifold, remove fuel rail (takes a reverse torx bit) and pull them out after unplugging the electrical connectors. You can have it all apart within a half hour. Then buy a can of injector cleaner and soak the injectors in it for at least a day. It is a good idea to replace the filter in each injector at the same time, they pull out pretty easily with a screw held in a vice-grip. Rebuild kits with new filters and o-rings are available, I got my kit for around $30 from RJM Injection Tech. You will want to install a new upper manifold gasket, Fel-Pro has an inexpensive one.

The off-the-shelf fuel injector cleaner kits don't seem to do the job usually. They just pass straight through the injector, whereas soaking the injectors gets all the built up sediment out, especially if you blast compressed air through the injectors (a simple 12v wiring rig can be made to open the injectors momentarily). Also the stock filters are often crudded up and deteriorated after this many years in service.

 

[Rupert8]

Thanks for all the input!

Murkinstock, I checked the fuel pressure regulator and it was indeed full of gas. I replaced it and will report back to see if it is the problem. If not, then it is certainly on to the fuel injectors.

Arco777, thanks for the advice - and the link. Pretty interesting. I don't have easy access to a workshop, unfortunately, but may still dive in on a thorough cleaning. I have looked around and see that local chains such as Meineke and Wheel Works all offer a fuel-injector cleaning service, seemingly involving an 'IV' into each cylinder. Does anyone have any thoughts on this process? It is around $100.

A couple of thoughts on the problem that I and, it seems, numerous other people seem to be having:

1) Instead of cooling when the engine is switched off, doesn't the temperature actually rise some since the coolant is no longer flowing? Maybe I have been heading in the wrong direction on this one.

2) When the problem occurs, after the engine has been off for around 20 minutes, I can leave it in park and rev the engine as much as I like with little or no improvement. The car seemingly has to move a few feet, with the accompanying increase in RPM, for the issue to clear up. Can this be related to the transmission in any way? With that, I am way out of my depth...

Again, many thanks for all the input from everyone who has responded. This is slowly getting worse and I do appreciate the advice. I'll keep this thread posted if there is any change....

 

[arco777]

I have looked around and see that local chains such as Meineke and Wheel Works all offer a fuel-injector cleaning service, seemingly involving an 'IV' into each cylinder. Does anyone have any thoughts on this process? It is around $100.

I would do some research on exactly how they do it. I am thinking it's more likely they drop a bottle of off the shelf FI cleaner in your gas tank. Since the cleaner technically does go through the injectors and the rest of the fuel system, and into the cylinder via the intake, maybe that is how they can claim what they do, but it may be no different than dumping a $5 bottle in yourself.

Realistically, the way an engine works, you can't clean the injectors from anything stuck inside the cylinders - if you somehow snaked in through a spark plug hole, you're still blocked by the intake valves. If those didn't exist, you still have to travel up the intake manifold somehow. No snake tool is going to come from that direction successfully, especially with closed valves. Additionally, no cleaning service is going to somehow remove the sediment that is trapped in the individual fuel injector filters without removing them and replacing the filters or reverse flushing them (requiring removal of the injector filter or energizing the injector while applying reverse pressure).

When the problem occurs, after the engine has been off for around 20 minutes, I can leave it in park and rev the engine as much as I like with little or no improvement. The car seemingly has to move a few feet, with the accompanying increase in RPM, for the issue to clear up. Can this be related to the transmission in any way? With that, I am way out of my depth...

Of my two Explorers, one I have cleaned the injectors on and it has no issues. On the other, it has had the issue you describe exactly for 4.5 years now. It hasn't gotten any worse in 35k miles since it started one day. I haven't serviced the injectors since then but I know everything else on the truck is 100%. Your transmission and mine are fine. It's a misfire that I believe to be caused by insufficient fuel flow/incorrect injector timing due to sticking. My theory is that the injector "sticks" thanks to gunk or sediment inside it, and while it takes very little fuel flow to rev the engine in park, it takes a greater quantity in Drive when there's a load on the engine. The injectors duty cycle lengthens and they overcome the sticking.

 

[Rupert8]

Hi,

So the fuel pressure regulator didn't fix the problem. I guess it is on to the injectors after this (somewhat expensive) process of elimination.

Could it be the fuel pump, though?

I'll keep this page informed in case it helps others....

 

[Rupert8]

Well, for some reason I went back and looked again at everything (before getting into pulling out the fuel pump/injectors). I noticed a tiny (and I mean TINY) crack on one of the spark plug wires. I changed them out and the problem hasn't returned since.

This might be a coincidence and I will report here if the problem returns but so far it has been a month with no issues on the rough idling.

I have some doubts about my fuel pump anyway, unfortunately, but this particular problem seems to have receded.

 

[murkinstock]

Good to hear!

 

[Rupert8]

Well, the dark days are back! Out of the blue the problem is back... Now I am wondering if it was a coincidence that it ever seemed to disappear.

I will look into the fuel injectors son unless there are any other ideas that have come up. I am not feeling too confident taking them apart but may well get going on it nonetheless.

Thanks again, all.