So driving my truck home today, f350 in sig with 460ci and 51k miles the coolant temp gauge never reached where it should be at operating temp, I drove the truck 35 miles home with outside temp 28*F the temp needle was about halfway between the C and N(for normal on gauge) the cab had good heat though.

Another issue is even after driving the truck 35 miles it idles high, in park it idles at about 1000 rpm and in drive its probably 900rpm

I have a feeling what going on here is that the computer thinks the truck is cold so its sending it into high idle, Could this be a faulty coolant temp sensor? I tried searching but cant find solid information, also in my searching it appears there are two coolant sensors, one temp sensor is for the computer and another is for the gauge but maybe those were for older efi 460's

could this be why my truck is constantly idling high?

 

Never trust the factory temperature gauge, it's for reference only. There is a different sensor that sends engine coolant temperature signal to the computer (PCM).

A high idle RPM can be caused by a vacuum leak or bad sensor. Check for codes first.

 

I don't believe there is a vacuum leak but I will check

no check engine light

I will scan for soft codes tomorrow and probably put a new coolant temp sensor and try to clean the iac valve, truck runs like a top other than the high idle

 

You can have a stored code or issue that would cause a failure in the KOEO tests without tripping the Check Engine Light. Run the KOEO tests and CM code display.

I would not waste a dime on parts until you check for codes, repair what may be flagged then recheck.

 

I thought this truck was obd2 since it's a my1997 but it's obd1 I found the plugs on driver fender, I've never pulled codes this way before but I'm gonna try

I watched a YouTube video about this basically I jump the wires then turn the key on and count the CEL flashes

What is cm mode display

 

Good info here Fuel Injection Technical Library » How To Run a Self-Test

 

Ok I tried counting the codes, I belive I have as follows

563- high speed electro-drive fan circuit failure
663- 4wd switch closed
411- cannot control rpm during koer low rpm check

I tried to take a video so maybe you guys could help me decode but I cannot upload it, also got the system pass 111 code

I dont feel any of these codes pertain to my 1000rpm idle concern

I started the truck and let it run a couple minutes, I then unplugged the IAC valve under the throttlebody, the truck bucked for about 5 seconds then died, that is good right? could that tell me its not pulling air elsewhere like with a vacuum leak

 

Ok I got the video uploaded here is a link to a video I took of all the codes flashing because I'm sure I missed one or counted wrong even though I did the koeo test 5 times and counted over and over
this is where the truck was idling today just below 1k mark now
[IMG][/IMG]

and I also found this thing blowing air out toward the fender
[IMG][/IMG]

 

ok some new info, I removed the bat cables to clear codes, replaced both coolant temp sensors and put a new 195* tstat in

truck now gets to operating temp and the temp gauge works, but the high idle problem is still there, it goes up and down also, in park it will slowly drop to maybe 800 rpms then go back up to 1000rpm

with truck cold unplugging iac valve truck runs for about 5 sec then dies

truck at operating temp unplugging iac valve truck will run for maybe a little more than a minute but rpms drop to about 750, and then slowly drop to around 450 until it chugs and dies

 

Mine had a high/rolling idle when the TPS went bad, but it also threw a code.

 

I'll check tps tomorrow and make sure it sweeps 1v-5v

 

tps checks out good, sweeps from 1.01v-4.78v

sprayed everything with brake clean and couldnt find anywhere sucking air

truck smells like its running way to rich

 

Your closed throttle TPS voltage is right on the border of being too high. I tried watching your video but I had too much buffering to get an accurate count. Once or twice I did see a code related to TPS output, but I would not be 100% comfortable to say it is bad.

I did notice your tach did not read Zero with the truck off?

Personally I have not had any success using the spray method to find a vacuum leak on a fuel injected engine. I find testing each vacuum circuit with a handheld vacuum pump/gauge is the only to know for certain.

If the PCM is sensing a lean condition, caused by unmetered air aka vacuum leak, it will dump in fuel to compensate.

 

Reading the flashes I get:
KOEO - 116 - Cold Engine coolant - ECT
KOEO - 636 - Cold Transmission oil - TOT
KOEO - 114 - Cold Intake Air below 50 deg F - IAT
CM - 111

OR
No Codes at all.

 

That is normal for air to come out of the Secondary Air Dump Silencer.