Rough Idle when warmed up

[hunt4lif3]

I'll give that a try maybe sunday or monday, I'm going hunting for the next couple days and wont really have time to work on the explorer. I ran the thing pretty hard today and noticed that the temp gauge never went past the o in normal and most of the time it was right below the n... also noticed that flooring it when starting from a stop on a hill it seemed to have very little get up and go power... dont know if any of that is related or gives you guys any ideas as what steps i might need to take to get the thing running right. thanks again for all the replies so far, i sure hope this thing gets straitened out soon.

 

[wood1]

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.

My Haynes manual seems to suggest you are correct. Easy to test, using an multimeter test the cold resistance of the sensor, should be around 40,500 ohms, warm engine it should be 3,800 - 1,840 ohms. (ref Haynes)

 

[gmanpaint]

When that sensor goes bad, the ECM does not know the the correct engine temp. It reads it as cold, when it is hot, and the wrong fuel / air mixture data is sent. This results in the "Sputter" that is happening.

 

[hunt4lif3]

You guys think I should change my thermostat too since the thing is running cool, or would that just be the sensor making it read cool

 

[wood1]

That sensor wouldn't have an effect on engine temperature. My ex runs around that same spot on the gauge. The computer watches that sensor and when the engine gets warmed up it allows the torque converter to lock. This helps the engine warm up faster, cats to light up quicker, less emissions. It also changes fuel delivery for different engine temps.

 

[RustySJohnson]

Yup, the little boot

Rusty had a rough idle when hot and it was the elbow to the vacuum line on the fuel pressure regulator I think he said. Got soft when warm and leaked. It's in his latest thread, "Elvira".

The rubber connector connecting the vacuum line to the fuel pressure regulator was soft and expanded when it was warm - thus loosing vacuum and not regulating the fuel pressure well. Idle was fine when cold, but after warm up it would take a few extra cranks to start and would idle rough. I went ahead and replaced all the rubber connections to vacuum lines and tree since they're purchased by the pack from the 'help' section anywho, it's a cheap and easy enough even if that's not the problem.

Edit: The symptoms you describe are identical to the problems I was having, I'm not sure where you're located geographically, but mine was a Florida find, maybe the warmer climate had something to do with the deterioration of the rubber components.

 

[huntman58]

I'll give that a try maybe sunday or monday, I'm going hunting for the next couple days and wont really have time to work on the explorer. I ran the thing pretty hard today and noticed that the temp gauge never went past the o in normal and most of the time it was right below the n... also noticed that flooring it when starting from a stop on a hill it seemed to have very little get up and go power... dont know if any of that is related or gives you guys any ideas as what steps i might need to take to get the thing running right. thanks again for all the replies so far, i sure hope this thing gets straitened out soon.

There are two temp sensors one with one wire (it runs the dash gauge only and that is what your reading inside) and the other one (has two wires and is the one the ECU uses) and is the one you want to change as its the one used for feed back to the computer. If not reading right maybe telling the computer the motor is too cold.

As you stand in front of the truck hood open facing the windshield it will be the one on your right, driver’s side of the thermostat housing. Yes the hardest one to get to as normal.
It’s also the one that was giving me the very same problems.

I would change it after you know for sure there is no vacuum leaks other wise your just running and chasseing your tail or as my dad would say peeing on a rope and watching it shrink

 

[hunt4lif3]

Changed both the ECT and IAT sensors and put in a new thermostat while i was at it... still got the rough idle...Could the fuel pump be causing the problem? even though it was recently replaced, I'm starting to think that its defective or something... I'm having "power surges" when going up hills now like the thing isnt pumping enough fuel to keep the thing running right, and sometimes i can take off and squeal tires and others it just lags along and then finally catches power, would that be a fuel pump issue or is my explorer just a piece of junk?

 

[hunt4lif3]

put a new fuel pump in it and the power is back, but the rough idle is still there.

 

[awood]

How about trying a KOER test. Maybe you can find something there if you haven't already tried it. Also, if you have an analog meter, perhaps try checking the TPS for smooth resistance changes as it's moved.

A new TPS fixed an erratic idle on my Ranger (same engine), but I hate to advise just throwing a part at it.

 

[hunt4lif3]

Tried the KOER test and go no results, also put a new TPS on it a month or so ago. about the only things a havent tried is a new egr valve a new distributor coil, and any of the o2 sensors, but it isnt throwing any codes at all.

 

[RustySJohnson]

Random codes, rough idle, misfiring.

I ran into this on my Mom's Ranger. It was a loose battery cable. Funny thing was, usually when this happens the starter doesn't work right. Not this time, it didn't have the 'juice' it needed to power the ignition coils. But this will run bad pretty much all the time. Not the same problem you have, but something to check.

Second, I saw someone mention 'heat soak', this is a real problem with injectors. This will cause it to idle rough when warm. Grab some replacements at your local boneyard, along with one of the connectors with long wires to hook up to a battery. Rebuild them with new pintles and screens. Soak them in carb cleaner overnight and back flow them with spray carb cleaner while pulsing them with 12V from your extra connector. Suspend them in an ultrasonic carb cleaner bath if you happen to have one. It's not a professional cleaning, but better than nothing. Again, this is something cheap, and couldn't hurt clean out the fuel system on a high mileage engine. There's a couple cool videos on youtube to demonstrate what I'm talking about. the pintles and screens run about $14 shipped.

 

[hunt4lif3]

would running some sort of injector cleaner through it help, or should I actually rebuild them?

 

[RustySJohnson]

Injector check

would running some sort of injector cleaner through it help, or should I actually rebuild them?

Injector cleaner certainly couldn't hurt. There's a lot of products out there, but my personal preference is Seafoam. If you haven't "Seafoamed" it yet, you're missing out. It brings the motor back to life, that stuff is amazing. Follow the instructions on the can, and there are a couple instructional video's on Youtube you can watch. If you have them out, you should recondition/clean them, rebuild is kind of misleading. Backflowing, ohm checking, that's really the secret. You should see the junk that comes out of those when you reverse flow them.

here's a link to where I purchase the rebuild kits:
http://www.bonanza.com/listings/Fuel-Injector-Service-Rebuild-kit-6-Cylinder-Engine-Bosch/52065711

I have a stockpile of injectors, I keep them around for just such occasions. I haven't serviced them with the rebuild kits yet, but they have been cleaned in an ultrasonic bath of carb cleaner and reverse flowed. PM me and we can work something out if you like.

 

[hunt4lif3]

Today i hooked up a vacuum gauge just to be sure there were no leaks i could have missed. With a cold engine i was reading 18-18.5" and with a warmed up engine it was steady around 20"...I did notice that when it was cold and started it up, it was idling around 1600 rpms and would slowly drop as it warmed up, but when it was dropping it acted like it was dropping too far and then it would rise back up then drop then rise, and while that was happening, the vacuum gauge was all over the place. Don't know if any of that info helps or not. I'm really wanting to lift this thing a little and don't wanna put the money into the lift unless it is running right, so I have to figure this out!

 

[bruce119]

Hi Just want to let you know I got the same thing. On my 93X sometimes when I start usually after warm. I get a rough idle more like a surging idle not a miss like your surging the throttle and I can smell it running rich. I rev it up and it clears out and it's fine. It just does it once in wile so I will read through this again and maybe find some direction.
Thanks

 

[arco777]

My 2dr 94 has done the warm restart rough idle thing for years. My 4dr 94 just started doing it as well. Randomly stumbles and sputters on a hot/warm start but clears up when you put it in gear and start to drive. Just ran Seafoam through it, both in tank and through vacuum. Got a little power gain but no effect on the hot start rough idle.

 

[RustySJohnson]

Clean injectors

We'll See if this is an injector problem. These were reverse flowed simultaneously in an ultrasonic bath for 45 mins a piece and ohm checked.

You'd never believe the crap that comes out of these when you do this. I have clear tubes on the connections so I can see what comes out of them. In the second picture is a screen I removed prior to servicing. As you can see, the screen is deteriorated to the point there's a hole in it. This is the reason to purchase the injector rebuild kits. Who knows how bad the previous vehicle ran or long this had been a problem.

 

[hunt4lif3]

Ok guys, with lots of help from everyone on this forum, and a huge help from RustySJohnson with injectors, I got the idle problem fixed! The injectors seemed to fix the rough idle when hot, but I had a rough idle on a cold start after the injectors were changed out. I think that was my own fault, because i found a small hole in one of the vacuum lines(I must have nicked it taking the thing apart). The injectors also helped my fuel economy tremendously! Before the swap I was getting around 160 to 180 miles on a tank of gas, I am currently sitting on half a tank or so and and I've already been 130 miles! That means I was getting roughly 10mpg before and now I'm getting around 15mpg! I'm so glad to finally have the problem fixed! thanks again for everyone's help!

 

[wood1]

Outstanding, glad to hear you have it fixed.