high idle problem on a 4.0

[mailboxman]

Hey Nhaz--it seems this is a problem that others have had on some of the other forums---One guy went to a junkyard and found all of the sensors and replaced them all and the high idle went away---I have replaced the coolant temp sensor and the IAC Valve--Did you replace any sensors before throwing the towel in and going with the toggle switch??? Maybe by process of elimination we can square it down to a single sensor??? I really dont want to put a toggle switch in--would much rather keep it stock

thanks to all

 

[mailboxman]

Update

I pulled the EEC out today at lunch--like I mentioned before--this truck is really clean and now rust or anything int the panel--I disconnected it (figured this would surely clear any bad codes--dusted it off real well and reattached. When I attached the single plug out of the left side, i saw the little red light on the eec flash momentarily--started truck and it idled perfectly--until I hit the gas and it went right back uo to the high idle---I am convinced it is one of the sensors but which one---i am going to try adjusting the TPS this weekend--i will drill the holes out bigger and see what happens--THIS IDLE IS POSSESSING ME!!!!!

 

[creepinjeepster]

I still suspect the TPS myself. There is a margin for the setting of the TPS. NOT an exact
.97V. It's just a matter of finding the happy medium for the truck. Mine is a .87 or .78. Can't remember for sure when I did mine, but if I try and adjust anycloser to .97, it does all kinds of stuff with the idle and acceleration and it throws a CEL.

Also, how are you setting your TPS? Check this site out here.
http://www.fordfuelinjection.com/?p=30
It will help greatly in setting your TPS. I should actually get someone to ad the site to the tech library for setting the TPS. As it shows above the charts, the setting can be ANYWHERE between 0.6-1.0 volts, but the closer to 1.0 the better.

 

[mailboxman]

Everyone Read This

I will probably get fired today because all i have been doing is looking up this freakin idle prob--read this--it makes sense to me because I have looked high and low for someone to say this

Question: 2002 Chevy Cavalier mileage: 70,000. My car's idle is supposed to be 900 rpm. Instead it idles around 1500 rpm. Also, it is a manual transmission and when I shift around 4000 or higher, the engine rpm remains high instead of going lower during the shift. I have replaced the IAC. I also have access to a Snap-On scanner. No codes are present and everything looks good. The scanner has the ability to vary the idle, which it does, but the idle is exactly twice as much as the scanner is programming it to do. I have checked the wire connections between the IAC and the computer and they are good. I have also checked the TPS with the scanner and the voltage and throttle position is accurate. At this point, I am leaning towards a computer. Thanks for any advice.

Answer: This is a difficult problem to detect because the computer can not sense a malfunction, the vehicles computer system thinks everything is ok. In reality what is happening is the electrical component inside the MAF sensor becomes contaminated by air impurities. These containments imbed themselves to the electrical component that senses the air flow causing the sensor to be slightly off, but not enough to trigger the MIL (malfunction indicator lamp). Replace the MAF sensor with a new. NOTE: (Mass Air Flow MAF sensor or Air Intake Sensor AIS, depending on manufacturer. It does the same thing only with different names).

 

[creepinjeepster]

If that's the case mailboxman, It should be possible to fix by cleaning the MAF with a sensor safe cleaner to remove these contaminants before spending the money to replace and see if it fixes the problem.

 

[Nhaz]

Hey Nhaz--it seems this is a problem that others have had on some of the other forums---One guy went to a junkyard and found all of the sensors and replaced them all and the high idle went away---I have replaced the coolant temp sensor and the IAC Valve--Did you replace any sensors before throwing the towel in and going with the toggle switch??? Maybe by process of elimination we can square it down to a single sensor??? I really dont want to put a toggle switch in--would much rather keep it stock

thanks to all

My high idle was a complete mystery to the first two mechanics I took it too. I am pretty sure they were idiots after listening to them talk about o2 sensors and how much that would cost => without ever pulling codes. the third I took it too showed me his 92 f150 with the exact same problem mine had. And then said he never figured out what the problem was Buuuut. Showed me the jury rigged toggle and at the time I needed the truck running like NOW so I went with that.

I eventually started testing sensors and everything was working as far as I could determine. What clued me in eventually was the screwy voltage that the IAC was getting from the eec-iv computer. It was all over the map nothing consistent. So I started checking grounds and finally pulled the panel off and saw what a pile of corrosion it was. I was amazed that the truck ran at all.


In the end I showed him what the problem was and maybe if he cared he could have a look at his own computer under that panel => I never found out he prollly never cared.

 

[mailboxman]

nothing works

cleaned the crap out of the maf and it didnt change anything--i have moved the tps to .8 and still runs exactly the same??? I wonder if it thinks its overheating all the time?? They say that will cause a fast idle---i am thinking it might be the eec--- I am stumped..

 

[Ranger44]

I don't get how you're adjusting the TPS on a 4L Ranger. The TPS's are non adjustable. Do not modify it to make it adjustable. Plus a DMM is limited on diagnosing a bad TPS, and so is a Scan Tool. There is an information delay and you can easily miss a dead spot. Find a shop with a lab scope. It has no lag and will pick it up.

You need to stop just testing sensors. They are a good place to start, but the circuitry is just as important. Have you tested the circuits between the sensors and PCM connector? High resistance or an open check are a must.

When the ECT has high resistance it thinks it's colder than shit outside. A complete open will make the PCM think it's -40F. High idle? Ya betcha.

How about that IAT sensor? Could also be reading a wrong temp? Hmmm?

OR you just have a sticky Throttle body or throttle cable. I'd look into this, especially if there aren't any codes........

 

[mailboxman]

the tps has enough play in it to turn it all the way to one side and get a .86, and a .96 the other way--i tried both settings and didnt change the idle--i cleaned the maf thouroughly twice and didnt change the idle--I tried another tps and it didnt change the idle-I am convinced no vacuum leak because as soon as i unplug the iac idle goes down. I also retorqued the intake bolts to spec--no change. The cold idle is 1500 and warm is 1200 so something is working and I wonder if the 1500/1200rpm has nay significance??(such as these would be the rpms in an overheat situation???? Can you tell me how to test the circuits between the pcm and sensors??? I will do it. Can you steer me to how to test the IAT and the ect--I will check them if I know how--all the wiring and underhood conditions on this truck are really clean as is the EEC and compartment around it--i pulled it out dusted it off and checked all connections--all look good. I have not replaced the iat sensor yet because i didnt see any reason too--if you can tell me how to check it i will---i dont want to put a toggle switch on the IAC and i will take it to a shop if I have to. I sure hate to let something like this beat me!!!!

 

[mailboxman]

Looks like I will probe the two wires going into the coolant temp sensor---when cold, one of the wires should have 5 volts??
The second wire should read something less than 5 volts?????

As engine warms up--first wire should show 5 volts
and second wire should keep decreasing in volts??

I will do this with a digital meter with black lead to negative on battery??

If any one can confirm this???
Is this basically the same test i do on the air temp sensor

I will do this early am tomorrow and post results

thanks

 

[Ranger44]

In order to test the ECT and IAT sensors you will need to set your meter to measure resistance. OHMS(omega sign). This is how those sensors work. As the temperature increase the resistance in the sensor decreases. It sends this resistance reading to the computer.

In order to check circuits between the sensor and PCM unplug the PCM connector. Set your meter for continuity and probe pins on the PCM connector and sensor connector. It'll beep if it's a complete circuit. Then test resistance. Shouldn't be much more than the resistance in you leads. Be careful not to widen out the pins by sticking the leads in. It's much easier to have the pin locations on a chart in front of you. A FORD EVTM is almost a must have. I've got the stuff sitting here. But that doesn't help you much, does it?

Also another thing to check for is lots of corrosion in the pins of the sensor connectors, and for broken connectors. Also make sure the pins aren't being pushed back in the connector when plugging it onto the sensor.

 

[mailboxman]

I probed both wires on the ECT--the first wire has 5.03 volts--the second wire has nothing with the engine cold.

I unplugged the sensor and checked for resisitance across the sensor terminals and got resistance (seems like the sensor is OK--brand new from Advance.

I backprobed the second sensor wire and I am getting full resistance to ground--so either this wire is grounded out or there is a short in the EEC????

Tomorrow I will hook back up to the output wire and get my resistance, and then unplug the wires (3 plugs) on the EEC and see if I still show resistance??

If resistance is still present, I will look for a shorted wire--if no resistance when EEC is unplugged I would assume that either EEC circuit for the sensor is damaged or something else is causing this load????

Any thoughts??? I am just guessing at this so would appreciate anybodies input

 

[Ranger44]

There is a chart. You shouldn't just assume a sensor is good since it's new. I've had a bad "new" sensor before. Chase that down.

That 5v is the reference voltage for the PCM. The other wire shouldn't have anything, it's the signal return.

Do you have a Chilton Manual for your truck?

 

[mailboxman]

negative on the chiltons--I cant find a book at the local auto parts since truck is so old--i should probably get one from e-bay----

When i probe the second wire on the Coolant temp Sensor--it shows no dc voltage--when key is on---maybe I should go to NAPA and buy another sensor???

 

[mailboxman]

I hate to ask this but is the PCM you are referring to the same as the EEC ???

I unplugged the three plugs on the EEC (this is the computer module behind the rear jumpseat on the drivers side) and I still show resisitance on the grey wire w/thin red stripe that goes to my engine coolant temperature sensor. I assumed this wire(gray w/thin red stripe) is the one that sends the feedback from the sensor to the computer????? When I unplugged the three plugs from the EEC (behind the driver side jump seat) I was still showing resisitance on the gray w/thin red stripe wire. I then assumed my wiring must be shorted???

I cant seem to find any bare or rubbed wiring--i had my wife stare at the ohmeter while i shook or moved every wire on the truck and needle never budged.

I wonder if I am looking in the right direction??? Is there another electrical part called the PCM that I need to disconnect???

Sorry for all the stupid questions--electronics like these boggle my brain--I am more adept at rebuilding an engine or even a carb!! I HATE ELECTRONIC PROBLEMS.