Poor low rpm performance, erratic idle

[rudypoochris]

I have a 1992 Ford Explorer. Just last week all of a sudden the car sort of fell flat on its face with the normal amount of throttle input to get it moving (I usually start moving the car around 650-800rpm). At first I thought maybe the car was cold, but the car continued to do this from stop signs even at full heat. I then noticed that the idle was sort of erratic with sort of up and down twitching on the tach, minimal, but definately there. The engine does not respond to instant throttle inputs nearly as well as before. If I dab the throttle the engine stumbles a bit, raises up, bumps up and down. In 1st cruising if I floor it at 1500rpm, the wheels don't chirp anymore, it lugs a bit and then gets power down. The rest of the RPM range seems to be okay. There is no check engine light on.

I am thinking this is just a dirty or clogged IAC valve? I ran the DVOM on it and the terminals read 9.8 ohms which is between the 7-13 ohm autozone.com says it should be. Could the IAC still be the cause or should I be thinking more towards a vaccum leak or EGR system issue? What else might cause this issue? Thanks!

 

[Donner]

Hi there... What fuel do you fill up on?

 

[rudypoochris]

Hi there... What fuel do you fill up on?

87 Octane Chevron, California Blend... running winter forumla now I would guess. Haven't experienced any ping at 3700rpm max load (3rd & 4th) like last year.

 

[Donner]

You have the best fuel, so you've eliminated a likely cause. There is a recent write up here on all the components to look at... Did you search Rough Idle? There are about 5 or 6 excellent write ups on what to look at... I'll post the link if you don't find it first...

 

[Donner]

Check this out... they will tell you to check before replacing. Good advice to follow...

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

 

[rudypoochris]

Hmmm. I replaced the plugs and wires within 6,000 miles ago but that is an easy check so I will do it. For the EGR stuff that may be more difficult to find out. I am unsure of how to clean an IAC although it was mentioned, any tips there might help. It could be the coil pack, but that would kind of baffle me as to why it happened all of a sudden and why it is low RPM and rough idle but pulls okay up top. I will check the MAF, that was also cleaned within the past 6-8 months.

 

[Donner]

Don't even worry about it... the people that know will chime in. It's in their blood!

 

[lnstevens1976]

Don't even worry about it... the people that know will chime in. It's in their blood!

"Coolant Temperature Sensor".

I had the exact same problem on my 1992. It won't through a check engine light if it "IS" reporting, but reporting wrong.

I.E. it is reporting the engine is 98 while it is actually 238 causing it to run rich.

Or it is reporting 98 when the engine is actually 32 causing not enough fuel.

That kind of thing.

Plus, it calibrates off the Air Intake Temp sensor which can cause issues.

 

[rudypoochris]

Well the dealer just called me and told me it failed to start... Really sucks. I feel that it probably was running rich since as soon as it starter up it would rev to around 3000rpm then attempts to settle.

 

[rudypoochris]

It was the ECT!

 

[Donner]

In the blood, man!

"Coolant Temperature Sensor".

I had the exact same problem on my 1992. It won't through a check engine light if it "IS" reporting, but reporting wrong.

I.E. it is reporting the engine is 98 while it is actually 238 causing it to run rich.

Or it is reporting 98 when the engine is actually 32 causing not enough fuel.

That kind of thing.

Plus, it calibrates off the Air Intake Temp sensor which can cause issues.

And there you have it... That amazes me!

 

[rudypoochris]

What was dumb is that I told the dealer to check two things. ECT and IAB. They said they cleaned the IAB but since it wasn't throwing codes they couldn't figure it out. At that point I knew it was the ECT b/c they said it wasn't starting after being on for a while. Immediately I used my DVOM on the sensor and it was reading 100 degrees off at heat. Unplugged the sensor, CEL came on car set into 672 idle again. So I replaced it. End of story.

Well I called the dealer and told them they sucked. That they charged me $100 to do something that didn't need to be done, etc.

 

[v1rotv2]

Having a brain block.

What is the ECT?

 

[rudypoochris]

Engine Coolant Temperature sensor

 

[suprcharg97]

There is one for the gauge on the dash coolant temp. sensor. the other ECT is used for the PCM in calibration for the fuel trims. I can't believe the exhaust wasn't black with over fueling concern. That is one indicator of the ECT has fail. As mentioned previous the PCM will not trip the mil because it still thinks it operating in normal parameters of the calibration. Your condition look liked it created a rich condition and flooded the vehicle.

 

[lnstevens1976]

There is one for the gauge on the dash coolant temp. sensor. the other ECT is used for the PCM in calibration for the fuel trims. I can't believe the exhaust wasn't black with over fueling concern. That is one indicator of the ECT has fail. As mentioned previous the PCM will not trip the mil because it still thinks it operating in normal parameters of the calibration. Your condition look liked it created a rich condition and flooded the vehicle.

These ECT do not always fail completely. When they actually fail completely it will through a check engine light, when they don't......

The other way they fail is to simply misreport the temperature. When they misreport the temperature it can cause any variation of problems, such as the one listed above. His was worse than mine as my problem was just the flat on the face at various temperatures when trying to put the throttle down and the rough idle.

From what I have been able to find out they can start at only a few degrees off and simply continually get worse.

 

[rudypoochris]

I can't believe the exhaust wasn't black with over fueling concern.

Don't believe it was.

That is one indicator of the ECT has fail. As mentioned previous the PCM will not trip the mil because it still thinks it operating in normal parameters of the calibration. Your condition look liked it created a rich condition and flooded the vehicle.

Yes. It went too rich and so it was bogging.

I scanned it with the multimeter to be reading 65 degrees or so when the coolant was 180 degrees which explains why it was a bit rough and wouldn't set to idle below 900 rpm. No biggie. Just replaced it thats all.

 

[steve53]

I believe that my ECTS may be giving me problems also. Is there a chart that I can use that tells what resistance equals what temperature? I have a rough idle, an occasional CEL which will clear itself sometimes, and an occasional lack of power on the highway where I have to floor the accelerator to climb hills. thanks.

Steve

 

[rudypoochris]

I believe that my ECTS may be giving me problems also. Is there a chart that I can use that tells what resistance equals what temperature? I have a rough idle, an occasional CEL which will clear itself sometimes, and an occasional lack of power on the highway where I have to floor the accelerator to climb hills. thanks.

Steve

I would see if you can get that engine code out of there, it will tell you right away. Here is the chart.

 

[steve53]

Thanks for the chart there Rudy. The code is very intermittent, it always clears when the key is turned off. I tried to read the codes with a scanner from the Schucks store down the street, but it would not work for some reason while doing the engine running test. I will check my readings and compare with the chart. Thanks again.

Steve