Operation: Smooth Idle

[96eb96]

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.

This is what a "real diagnostic" is, rather than a shadetree who just reads codes and flips parts. A real datastream with all the ford data shows many little pieces of info that could help solve issues.

 

[waskly]

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! :

its a characteristic of the trucks idle, it is a normal condition and every ex has it. one is due to a low idle, 2nd is you have a rack a pinion. even pop the hood, that engine does move when running at idle rev it up that movement disappears.

 

[waskly]

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

the oscilloscope on the ids or the wds version never would pick it up.

a real 4k up oscilloscope might but i doubt it since it would have to be analog not digital, i have never seen in a dealership someone use one.

its the most misleading tool to 95% of the techs out in the real world.

also since air, baro, load, temperature, all affect how o2 work, if you need something so fine that the pcm on the data stream dont see, then no that is not the problem.

 

[waskly]

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.

the pcm is open loop till ect tells the pcm to close loop, what it means is engine is at normal operation temp, take control, what you will notice once that happens is the car will imo have a low idle, if you could, which you cant with a tuner, raise it by 50-100 rpm you would never feel it.

 

[mistertonylee]

Hi guys. Just want to let you know that not all explorers have the rough idle. Mine idles at a steady 650 rpm when warm, 900 or so when cold, with no vibration or roughness. Don't know how it does it, but I've never had a problem with it, so it's possible. It's a '99 SOHC.

 

[2000StreetRod]

O2 sensor heater warm up

On my 2000 Sport the PCM is only in open loop at cold start until the heaters on the O2 sensors warm them. My A/F ratio meter has a 20 second time delay after engine start before displaying a reading. I can see the cycling of the A/F ratio (closed loop) in less than a minute after engine start.

The crankshaft position sensor, ECT sensor, PCM and IAC valve are the main control system components at idle. The crankshaft position sensor allows the PCM to determine engine rpm. The PCM determines the desired idle speed based mainly on engine coolant temperature and commands the IAC valve accordingly. Idle speed is also adjusted for engine load based on A/C compressor on/off and automatic transmission engaged/disengaged.

Some people are not aware that the A/C compressor is activated/deactivated periodically for various positions of climate control airflow selection (i.e. defrost).

If the throttle linkage does not return to the same closed position then the TPS will generate a different voltage at idle. It may take the PCM a detectable interval to adjust to the new idle value. There is also a firmware damper to prevent the engine from stalling when letting off the accelerator and quickly stopping the vehicle. You may want to try cleaning the throttle plate, lubricating the throttle linkage and testing the TPS output voltage to see if it is consistent when returning to idle.

Another thing to check is the operation of the EGR valve. It is supposed to be closed at idle.

 

[98EdBomber]

Hi guys. Just want to let you know that not all explorers have the rough idle. Mine idles at a steady 650 rpm when warm, 900 or so when cold, with no vibration or roughness. Don't know how it does it, but I've never had a problem with it, so it's possible. It's a '99 SOHC.

Thank you.

 

[98EdBomber]

[/QUOTE]The crankshaft position sensor, ECT sensor, PCM and IAC valve are the main control system components at idle. The crankshaft position sensor allows the PCM to determine engine rpm. The PCM determines the desired idle speed based mainly on engine coolant temperature and commands the IAC valve accordingly. Idle speed is also adjusted for engine load based on A/C compressor on/off and automatic transmission engaged/disengaged.

Some people are not aware that the A/C compressor is activated/deactivated periodically for various positions of climate control airflow selection (i.e. defrost).

You may want to try cleaning the throttle plate, lubricating the throttle linkage and testing the TPS output voltage to see if it is consistent when returning to idle.

Another thing to check is the operation of the EGR valve. It is supposed to be closed at idle.[/QUOTE]


1. It's odd that a DTC may not be set if the ECT, CPS, PCM, IAC, were malfunctioning. ECT sensor changed when thermostat housing replaced.

2. Throttle bottly cleaned and lubed. I believe it is closing but theres really no way to inspect with the engine running. With the air tube off, It appears to be closing all the way.

3. It will HOLD a steady rpm - just vibrates in and out.

4. How would I go about inspecting if the EGR is closed?

5. I heard the A/c compressor "clicking" on and off. The outer plate moves in and out and "clicks" when pulled inward. Seems a little loud to me but maybe its normal. I got curious one day because I started hearing a clicking noise. Sure enough, A/C compressor outer plate.


Thanks.

 

[98EdBomber]

the pcm is open loop till ect tells the pcm to close loop, what it means is engine is at normal operation temp, take control, what you will notice once that happens is the car will imo have a low idle, if you could, which you cant with a tuner, raise it by 50-100 rpm you would never feel it.

Interesting because like I said when it is warming up at about 1000rpm it doesnt have the vibration. Only when oper. temp. is reached. Kicks down to around 700-750 rpm and starts to vibrate.

NOTE: I did, however, adjust the idle screw in case the IAC craps out. I don't believe this should have any affect on the idle because it had the vibration before the adjustment. I just have the peace of mind knowing if the IAC dies, the engine won't stall. Thanks to the info. on this site for the tutorial on adjusting idle screw.

Idle speed is not adjustable to my knowledge.

 

[98EdBomber]

its a characteristic of the trucks idle, it is a normal condition and every ex has it. one is due to a low idle, 2nd is you have a rack a pinion. even pop the hood, that engine does move when running at idle rev it up that movement disappears.

Well maybe I'm in denial...LOL..but determined nevertheless.

 

[98EdBomber]

This is what a "real diagnostic" is, rather than a shadetree who just reads codes and flips parts. A real datastream with all the ford data shows many little pieces of info that could help solve issues.

True, I could spend the $100 - But with 150K miles on her I think its time for a major tune-up anyways. If push comes to shove and I can't figure it out with replacing "tune-up" parts then I may have to go to a dealer and get her "diagnosed".

Thanks.

 

[98EdBomber]

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.

Can you remember exactly what parts you have replaced?

There are so many things that could be a possibilty and I had to narrow it down by trial and error and perhaps the expensive way but I now have peace of mind to know that it has a major tune up.

Im thinking O2 sensors. In my situation, this made the most improvement.

Good Luck.

 

[waskly]

Interesting because like I said when it is warming up at about 1000rpm it doesnt have the vibration. Only when oper. temp. is reached. Kicks down to around 700-750 rpm and starts to vibrate.

NOTE: I did, however, adjust the idle screw in case the IAC craps out. I don't believe this should have any affect on the idle because it had the vibration before the adjustment. I just have the peace of mind knowing if the IAC dies, the engine won't stall. Thanks to the info. on this site for the tutorial on adjusting idle screw.

Idle speed is not adjustable to my knowledge.

idle screw does nothing but throws the car out of tune, the pcm will every key cycle set close throttle reference voltage. and the pcm will still go for the desired idle speed.

 

[waskly]

Well maybe I'm in denial...LOL..but determined nevertheless.

good luck in your search, but its how these trucks are.

 

[Explorer '96]

How much better did checking these things do to your idling? I have the same symptons.

 

[98EdBomber]

idle screw does nothing but throws the car out of tune, the pcm will every key cycle set close throttle reference voltage. and the pcm will still go for the desired idle speed.

http://www.explorerforum.com/forums/showthread.php?t=262930


Then can we say this ^^^ procedure is incorrect?

And also the set screw is not interferring with the plate. Ill check it again today. Thanks.

 

[Explorer '96]

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.

How do you test the voltage on the o2 sensors?:exp:

 

[96eb96]

How do you test the voltage on the o2 sensors?:exp:

i use www.obd-2.com with a pwm-iso blue router (or the CAN interface - its more money- you can use it on newer cars too). It is a real graphing scan tool with every ford parameter. You leave a laptop on the passenger seat, drive around and then look at the graphs(or have someone else drive).

You can read stuff like Baro, egr, even ABS codes! It gives you access to every FORD parameter your car has(from a library of 1500!). You can watch misfire counts.

Its not a toy but for the money (under $150) its as close to a dealer scan tool as you can get. The $100 scan tools at walmart are garbage. The site looks 15 years old but the product is no nonsense and powerful.

This tool will tell you if an o2 sensor fades in and out. You can watch the graph. I helped people find stuff with this tool that the dealer couldn't. You can log hours of data with it.

The other thing you have to get a Ford Service manual from Ebay on CD or DVD. Between the CD and your scan tool you never have to be at the mercy of mechanics again. The CD teaches you strategy for diagnosing issues. From what I see with others is that unless you know a very good tech chances are you are going to have a major vacuum leak from your wallet if you depend on them for diagnostics.

 

[waskly]

http://www.explorerforum.com/forums/showthread.php?t=262930


Then can we say this ^^^ procedure is incorrect?

And also the set screw is not interferring with the plate. Ill check it again today. Thanks.

you get a lean codes, or the pcm will just adjust the fuel to the incoming air. other words will do nothing. i think pre 97 or 96 trucks this might work, since that pcm could be the odb 1 had pre defined values. i know later the tps was set with key cycles. sets codes when played with while running also.

in the end, its not even worth playing with.

 

[96eb96]

you get a lean codes, or the pcm will just adjust the fuel to the incoming air. other words will do nothing. i think pre 97 or 96 trucks this might work, since that pcm could be the odb 1 had pre defined values. i know later the tps was set with key cycles. sets codes when played with while running also.

in the end, its not even worth playing with.

THe idle screw shouldn't be touched on EEC-V cars(96+). The service manuals are adamant about that. Even newer EEC-IV says to leave that screw alone. The IAC is a closed feedback system that adjusts airflow and idle speed. If you are idling too fast something else is amiss in the system.

I've seen that screw set procedure as stated for older CFI cars without IACs.