Operation: Smooth Idle

[98EdBomber]

1998 Ford Explorer 2WD 4.0 SOHC Auto w/ 151,00 miles. I have owned the vehicle since it had 23K and have done periodic tune ups according to service manual. Oil change, filter, air filter, brakes, etc, etc...

Symptom : Engine vibrates when warming up.

Occurs on cold or warm start up. On a cold start up the idle will start out at a stable 900rpm and vibrate more than normal.

After warm up temp is reached it settles down to 650-700rpm and smoothes out but still NOT where it should be.

Replaced parts:

battery
alternator
Motorcraft spark plugs - gap .054
Bosch spark plug wires - Tested and no arcing
Coil pack - Tested Primary and Secondary Resistance - Within Spec -
O2 sensors (All 4)
IAC Valve
thermostat and housing (TSB Fix) - Coolant system Flush -
PCV valve
Intake gasket Fix - FORD TSB - Uppers and lowers,galley plug, tensioner, oil restrictor
New oil and filter(motorcraft) - 5w30 Valvoline Full synth oil
Fram Air Filter
Fuel Filter - Changed about 15K miles ago
Changed Tranny fluid and filter
ECT Sensor
IAT sensor - Tested - within spec
TPS sensor - Tested - within spec
Cleaned throttle body - Very minor build up - Lubed linkage -
MAF - Cleaned and tested voltage - Within Spec -
Fuel Injectors - all clicking
Fuel pressure - Within spec

Fuel Injectors Cleaner - Every 3-5K miles from day one
Exhaust system - No leaks
Catalytic Converter - Removed for tranny fluid change - Inspected and appears to be fine (No rattling)

Vacuum system - Tested with Propane and Carb Cleaner - No apparent leaks



UPDATE July 28, 2011

Shaky idle and vibration throughout cabin have increased over the last 5 months. Still gets the same gas mileage and no problems running or starting.

UPDATE: Jan 27, 2011

Last item replaced were O2 sensors. This made the most improvement. There is still a slight stumble at stop lights.

UPDATE: Feb. 4, 2011

Replaced IAC Valve and the idle seems to have been improved but the vibrations dont seem to be completely eliminated.

UPDATE Feb 16, 2011

Idling issue has been improved yet the engine has its moments that it will vibrate. Especially now when warming up.

 

[SDR]

I've got the exact same idle too with same symptoms with 131,000 miles. I hope you figure it out cuz I'm getting tired of trying. My idle problem started about 8k miles ago.

 

[waskly]

its normal.

 

[swetrid]

Sometimes the o2 sensor dies for short times which causes fuel trim adjustments. Usually they die sporatically and pcm adds fuel which creates rough idle and then goes away once o2 sensor switching returns. Usually you need scan tools and a good road test while it occurs to pick it up.

 

[techieman33]

check out some of the threads that aldive made, he did a lot of stuff to try and achieve a smooth idle.

 

[waskly]

Sometimes the o2 sensor dies for short times which causes fuel trim adjustments. Usually they die sporatically and pcm adds fuel which creates rough idle and then goes away once o2 sensor switching returns. Usually you need scan tools and a good road test while it occurs to pick it up.

oh really and what scan tool will rms pick this up? i know that wds, ngs, pds, ids will never find this, if its long enough to data capture it sets a code.

 

[tgreene92]

at a 151k this is normal, even after fixing everything related like you did. may sound stupid and probably have already, but make sure all plug wires have good connection and that none are burnt or frayed since some run close to the exhaust manifold this happened to my buddies mountaineer. also make sure you didnt damage the filament in the MAF while cleaning it and make sure you properly cleaned the IAC, theres a thread on how to correctly clean it somewhere. you would most likely know due to hearing it, but have you checked for exhaust leaks, or a possible crack in the exhaust manifold. the tiniest crack in the exhaust manifold may not make a crazy loud noise but could cause a rough idle. id also inject the sea foam straight into the throttle body, doing it through the brake booster will only clean out one side of the engine. good luck, ive given up on my idle issues, its just a never ending adventure of time and money.

 

[2000StreetRod]

Al's smooth idle solution

check out some of the threads that aldive made, he did a lot of stuff to try and achieve a smooth idle.

As I recall Al Franklin never revealed the secret to the rock stable idle he was able to achieve. He had generated his own custom tunes for several years. He stated that his ignition coil upgrade helped some but not enough to satisfy him. Eventually he posted his upgraded throttle body for sale so I doubt that helped. Unfortunately, now we'll never know his solution.

 

[96eb96]

oh really and what scan tool will rms pick this up? i know that wds, ngs, pds, ids will never find this, if its long enough to data capture it sets a code.

a graphing scan tool could. You could have an o2 sensor sleep for just enough time NOT to trigger a code.

 

[96eb96]

some cars also shake if motor mounts arent perfect. Don't know if its the case with those engines however. Something to consider too...

 

[98EdBomber]

its normal.

Well it does run fine. 18 - 19 mpg.

The only thing I see wrong with this statement is the fact that there are moments of smoothness.

The fact that it slips into a smooth idle tells me there is potential to reach the "sweet spot". When it smooths out you can barely feel the engine running. Like the day I drove it off the lot. I think we all know what a smooth idle feels like compared to a rough idle. I think the "it's normal" folks out there have just given up. I, sir, am not a quitter! :

 

[98EdBomber]

As I recall Al Franklin never revealed the secret to the rock stable idle he was able to achieve. He had generated his own custom tunes for several years. He stated that his ignition coil upgrade helped some but not enough to satisfy him. Eventually he posted his upgraded throttle body for sale so I doubt that helped. Unfortunately, now we'll never know his solution.

Excellent write up indeed. Only exception is that there is a pronounced vibration that is felt on the dash, floor and also can be felt through the steering wheel. Al's idle i dont think was as stumbly as mine. Thanks Ill put a link up anyways.

Heres the link : http://www.explorerforum.com/forums/showthread.php?t=169335&highlight=quest

 

[98EdBomber]

some cars also shake if motor mounts arent perfect. Don't know if its the case with those engines however. Something to consider too...

Actually I just checked motor mounts yesterday. It was just a visual inspection. No cracking, etc. Even took a wrench to them and they don't seem loose. Is there a proper way to diagnose a bad one? If it were bad I am wondering how this would cause the idle to become intermittently rough? Wouldn't it cause a continuous shake? Thanks for the advice.

 

[98EdBomber]

at a 151k this is normal, even after fixing everything related like you did. may sound stupid and probably have already, but make sure all plug wires have good connection and that none are burnt or frayed since some run close to the exhaust manifold this happened to my buddies mountaineer. also make sure you didnt damage the filament in the MAF while cleaning it and make sure you properly cleaned the IAC, theres a thread on how to correctly clean it somewhere. you would most likely know due to hearing it, but have you checked for exhaust leaks, or a possible crack in the exhaust manifold. the tiniest crack in the exhaust manifold may not make a crazy loud noise but could cause a rough idle. id also inject the sea foam straight into the throttle body, doing it through the brake booster will only clean out one side of the engine. good luck, ive given up on my idle issues, its just a never ending adventure of time and money.

Thanks. I'll check the exhaust manifold tomorrow and see what I come up with. May as well check the torque of the bolts while I'm there. Thanks for the advice. I have properly replaced and cleaned every part.

 

[alohamonte]

I chased a rough idle for nearly two years and its finally smooth.

1. replaced the MAF and IAC - cleaning didnt work for me
2. replaced the air charge temperature sensor
3. replaced the idler pully, belt tensioner, and belt
4. plugs, wires, pcv, seafoam, fuel filter, air filter, degreased engine
5. replaced alternator and battery
6. replaced many of the Emissions systems components (solenoid, sensor, etc)
7. replaced upper intake gaskets, cleaned injectors and replaced 0-rings
8. synthetic engine oil

Some aspects were more effective than others. 1, 2, 4, and 7 were the big ones for me where I felt an immediate improvement.

 

[98EdBomber]

I chased a rough idle for nearly two years and its finally smooth.

1. replaced the MAF and IAC - cleaning didnt work for me
2. replaced the air charge temperature sensor
3. replaced the idler pully, belt tensioner, and belt
4. plugs, wires, pcv, seafoam, fuel filter, air filter, degreased engine
5. replaced alternator and battery
6. replaced many of the Emissions systems components (solenoid, sensor, etc)
7. replaced upper intake gaskets, cleaned injectors and replaced 0-rings
8. synthetic engine oil

Some aspects were more effective than others. 1, 2, 4, and 7 were the big ones for me where I felt an immediate improvement.

Is there a DIY way to clean injectors without having them reflowed?

I plan on replacing the O-rings next. I've used gas treatment "injector cleaner" every 3-5K miles but I was told it is really diluted stuff.

Also I'd like to know why you had to replace the idler pulley? I know I had my belt tensioner replaced at about 40k miles because it simply wore through the casing from the vibration. Which reminds me...HA...Made it 5 hours to a ski resort and 90 miles from home on the way back it failed....Anyone that has ever had this happen knows how scary of a sound it makes and EVERYTHING shuts down as the belt falls off. Luckily nothing was damaged. Got a friendly tow home and was all set after a new one. The new one has been on there ever since which recently started to rattle a little but i took it out and somehow got some lube in the bearing and it quieted it down a little. I may be replacing it soon too.

ps. Not sure I am aware of what #2 is. Did you mean the IAT (Intake air temp. sensor)?

 

[98EdBomber]

a graphing scan tool could. You could have an o2 sensor sleep for just enough time NOT to trigger a code.

Sometimes the o2 sensor dies for short times which causes fuel trim adjustments. Usually they die sporatically and pcm adds fuel which creates rough idle and then goes away once o2 sensor switching returns. Usually you need scan tools and a good road test while it occurs to pick it up.

From my understanding the PCM is in an "open loop"? (or closed loop - not sure) when the engine is warming up and during this time the PCM is not reading the O2 sensors and using stored parameters. This may just explain why the idle is fine while it is warming up at 1000rpm's and then when it warms up and the O2 sensors kick in, they malfunction - causing the stumble. I may have a defective O2 sensor. Thanks for the insight.

 

[janolsson]

I read a post somewhere about adjusting the TPS to bang on 0.95V to help smooth out idle. can't remeber what the spec range is but the thread i read suggests just a small change can make a world of difference. Sorry i can't remember which 2 terminals to measure across but it was on this forum so a search may yield the info.

 

[2000StreetRod]

TPS ratchet routine

I read a post somewhere about adjusting the TPS to bang on 0.95V to help smooth out idle. can't remeber what the spec range is but the thread i read suggests just a small change can make a world of difference. Sorry i can't remember which 2 terminals to measure across but it was on this forum so a search may yield the info.

According to the Ford strategy (PCM firmware) source code there is a ratchet routine that reads the TPS output voltage when the ignition is switched to run and assumes the value to represent idle. The PCM compares the value to a stored upper and lower limit to determine if within allowable range. If not within allowable range a DTC is set. The PCM periodically compares the initial TPS idle voltage with the current voltage. If a lower value is found then the PCM establishes it as the new idle voltage. It is no longer necessary to enlarge the mounting screw openings on the TPS to set the TPS idle voltage to a specific value.

 

[Paraphoe]

Excellent write up indeed. Only exception is that there is a pronounced vibration that is felt on the dash, floor and also can be felt through the steering wheel. Al's idle i dont think was as stumbly as mine.

Subscribing. My truck has this identical issue. This is the first time I've heard another member describe it exactly. It's that same vibration you can feel in the dash, floor, and steering wheel, and it comes and goes with seemingly no rhyme or reason. It's really bugging me.