High Idle

holyford86 · Nov 15, 2007

Pretty recently I have been having issues with a high idle (about 1500 rpm) I checked the voltage at the tps, its at about .925 volts. The Iac is not sticking open and it is relatively new. There are no vacuum leaks that I know of. The truck and engine are from 86, the wiring harness and computer are from an 87. The egr system was removed before I got the truck about three years ago but this never gave me a high idle before. The only other code I'm getting right now is one for vss circuit open.
The 86 didn't have a vss from the factory and the open vss code just popped up about a month ago even though there hasn't been a vss hooked up to it since I put the wiring harness in about 2 years ago. Could this cause my high idle? I don't know anything about how this particular circuit is used by the computer so I'm at a loss. Is there anything else that could be causing the high idle that I could test to figure out if, it is bad? Or could this condition be attributed to the fact that the motor has 263k miles on it?

Psychopete · Nov 15, 2007

Do you have any popping at idle? If you do, it's probably vacuum leak. Especially if the plenum gasket has been reused.

What is the actual code #?

From what I've read the VSS is more or less used for cruise control. I am not %100 on that, though.

Throw a vacuum gauge on that mug, that might help narrow down which system is malfunctioning. I've also heard of non-OEM IACs not lasting too long either, not sure if that's the case?

Pete

holyford86 · Nov 15, 2007

Plenum gaskets were replaced when the distributor was pulled to replace the pickup coil. The condition existed before that though so I don't think that was the issue. Is there some way to check the internal resistance of the IAC to see if it is bad? I think its alright because at idle if you put your finger over the port that the IAC draws from, it hardly pulls any vacuum at all but if you snap the throttle to WOT it will pull a good vacuum. You can hear it when you first start the truck as well. If the neutral safety switch was bad would it cause something like this? The truck was in gear when I pulled the codes, Both KOER and KOEO, oversight on my part so the code was there and I overlooked it.

Natedog · Nov 26, 2007

Did you get this figured out yet?

holyford86 · Nov 27, 2007

might have, I have tested all components that would be related to it and have done some research and have concluded that the vss does play a part in how the idle is handled, not where it idles just how rapidly it drops after you push in the clutch. so I'm going to put in a vss and its associated cable and see how it is, and if it does anything at all. The current speedo cable is nearly shot anyway so i'm really not throwing much for unnecessary stuff at it.

Natedog · Nov 28, 2007

Searched and found this interesting site regarding Ford vss, efi and other sensors:

http://fordfuelinjection.com/?p=33

The Vehicle Speed Sensor (VSS) is a small signal generator that is turned by a gear inside the transmission assembly. The Vehicle Speed Sensor produces 8 pulse per rotation which a stock computer assumes 8000 pulses per mile. The Vehicle Speed Sensor (VSS) is a variable reluctance sensor that generates a waveform with a frequency that is proportional to vehicle road speed. When the vehicle is moving slowly, the sensor produces a low frequency signal. As the vehicle speed increases, the sensor produces a higher frequency signal The Vehicle Speed Sensor (VSS) supplies this signal to the components that require vehicle speed information including the speed control amplifier for cruise control equipped vehicles and computer. The computer uses the VSS signal for emmisions contol programs and speed limiters. The emmisions programing can cause a manual transmission vehicle to stall out while decelerating if no VSS is used.

holyford86 · Nov 28, 2007

Yeah, I realized I'm an idiot. I was reading another post in another thread in the 2.9 forum (http://www.therangerstation.com/forums/showthread.php?t=3027), AllanD was saying how much of a difference an improperly functioning (or in my case previously removed) EGR system will affect how the 2.9 runs, It made perfect sense to me. I must have been in a drooling stupor when I decided that the VSS will affect the engine to much of a degree. I installed a computer out of a 1988 ranger 2.9(no EGR) and the idle speed and how the idle is handled is substantially better than it was before. Not to mention the slight increase in midrange power due to the fact that the computer wasn't looking for or trying to use the nonexistent EGR system. The idle is still a hair high for my liking (~1100 RPM) but as the computer "learns" my sensors it might drop. I'm still going to install the VSS and such out of curiosity.

Natedog · Nov 29, 2007

Thanks for the update, great info...keep it coming as things change or not.

holyford86 · Nov 29, 2007

Im not recommending that you swap to an 88 computer in your 86 or 87 but its what made the most difference to me, in my experiences. Im going to check my tps baseline today and adjust as necessary, that may bring down my idle a bit.

High Idle

holyford86

Some guy with a problem

Psychopete

Well-Known Member

holyford86

Some guy with a problem

Natedog

New Member

holyford86

Some guy with a problem

Natedog

New Member

holyford86

Some guy with a problem

Natedog

New Member

holyford86

Some guy with a problem

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