Air Bypass Valve Voltage info needed

[DangerRanger2.9]

Hello all,
I am having problems with my 86 2.9L. I have only owned this truck for a few weeks, so i am still getting to know it (first ranger, first OBD I vehicle). The truck has idled high since i got it, it idles the normal 1100-1200 on cold start up, then when the engine comes up to temp it bumps up to 1300-1500 idle, and stays there. The TPS is at .86 volts at idle, which i understand is a little low, but within range? The throtle body is clean, both sides of butterfly. So i checked my Idle Air Bypass Valve, at idle i unplug it and nothing changes what so ever. Then cleaned IABV, no change. Then replace IABV, no change. Still can unplug at idle and does nothing. Check voltage at IABV, 13.2 constant volts at idle. From what i gather, it should be a constantly flucuating 0-12 volts? What would couse the constant 13.2 volts? I can lower my TPS to .70 volts, and she idles at 800 or so RPM, much lower volts and she just dies. sorry for the long post, and thank you for your inpute. P.S., no i havnt had a chance to check codes. And yes i disconected battery to reset system everytime i did some thing. Thank you.

 

[Psychopete]

You will have battery voltage constantly at the IAC at the red wire when the key is on run. Wiring diagrams are really helpful w/ diagnosing EFI problems understanding how the circuit actually works. Bet you have a vacuum leak. Computer has adaptive learning, no need to reset it. Actually can make things worse sometimes, the computer stores base voltages and it may store a value of a bad sensor which would prevent it from throwing a code later on. Also check for codes, KOEO/CM and especially KOER when the engine is warmed up.

 

[DangerRanger2.9]

Thank you for the info, i will move on to vacuum leaks and codes, and go from there.

 

[Psychopete]

The 86-87s don't have functioning check engines lights.. It can throw codes with out ever indicating that it sees a problem. If you get a 41 in CM good chance it's a vacuum leak - this says oxygen sensor read too lean, and it most cases it's read too much oxygen in the exhaust. But will just have to see what you come up with.

 

[DangerRanger2.9]

have only done KOEO code read, pass on the KOEO test, Memory test got code 33 (EGR did not open intermittently - EVP EVR PFE). also code 63 (TPS signal too low)- could be explained by me fooling with TPS. And code 18 (Ignition TACH signal erratic - Ignition Systems)- could be explained by my ignition actuator(in the steering colum) cuting in/out, it is now fixed. Also checked for vacumme leaks, could find nothing. I can take intake hose off, put hand over throttle body at idle, which is 1300 rpm, and choke the engine till it dies. When i do this i hear a loud whistle (air flow) at the IAC. The IAC that i got at Napa is a little different from stocker it replaced. New one has a black breather on it, that is where the air leak comes from when i cover the TB. Also, when i adjust the TPS idle screw to get the TPS to read around .8 volts, i can see the TB butterfly is open enough to let quite a bit of air thrue. Is TPS just reading too high volts, therfore when tps is at correct volts, really the butterfly is open a little and letting all the air in? If i adjust TPS to anything lower than .8 volts, it idles down to about 1000 rpm, but wont idle when cold. Also, if you unplug wire harness from TPS, should anything happen? Nothing happens with mine, idle does not change, i can rev engine just fine. No difference whether IAC, or TPS is pluged in. Will try to get KOEO codes tonight. Sorry for the book i just wrote. thank you for the ideas.

 

[holyford86]

have only done KOEO code read, pass on the KOEO test, Memory test got code 33 (EGR did not open intermittently - EVP EVR PFE). also code 63 (TPS signal too low)- could be explained by me fooling with TPS. And code 18 (Ignition TACH signal erratic - Ignition Systems)- could be explained by my ignition actuator(in the steering colum) cuting in/out, it is now fixed.

Your code 18 may be caused by a bad IDM resistor, it should be located in the main wiring harness where it runs near the power steering pump, it will be a brown rubber block with a squiggly line on it. If you ohms test it it should come out to 22k ohms +/- 20%. If it tests bad, go to radio shack and get the biggest 22k ohm resistor you can find and SOLDER it into that wire, then heat shrink it.

The IAC that i got at Napa is a little different from stocker it replaced. New one has a black breather on it, that is where the air leak comes from when i cover the TB.

It's going to make noise when you do this, mine does.

Also, when i adjust the TPS idle screw to get the TPS to read around .8 volts, i can see the TB butterfly is open enough to let quite a bit of air thrue. Is TPS just reading too high volts, therfore when tps is at correct volts, really the butterfly is open a little and letting all the air in? If i adjust TPS to anything lower than .8 volts, it idles down to about 1000 rpm, but wont idle when cold.

the way I have always set my TPS baseline is this: Run the engine long enough to get it up to temp, shut it off. Unplug the IAC, restart the engine, run it @2000 rpm for about 30 seconds, let off, adjust the idle to 600-650 RPM, shut it down. Restart the engine, run it at 2000 rpm for about 30 seconds, let off and check the idle, if it remains @600-650 rpm shut the engine down, reconnect the IAC, disconnect the battery for more than 10 minutes, reconnect the battery. It should be idling in the 800-900 RPM range if all is well. If it isn't you may have a problem elsewhere (vac leak) that needs attention. I have found the exact TPS voltage can vary when using this procedure but it's usually within the .800-1.000 range.

Also, if you unplug wire harness from TPS, should anything happen? Nothing happens with mine, idle does not change, i can rev engine just fine. No difference whether IAC, or TPS is pluged in. Will try to get KOEO codes tonight. Sorry for the book i just wrote. thank you for the ideas.

The idle should drop when the IAC is unhooked, check the IAC as follows: There should be greater than 10k ohms between either IAC pin and the housing. The resistance between the IAC pins should be between 9.5 and 11.5 ohms. The red wire is a battery constant wire it should have at least 12 volts KOEO, The gray wire (ground) is what controls the IAC

PM me if you would like a wiring schematic of the engine controls

 

[DangerRanger2.9]

Hey thanks holyford86, that is some great info! Ok, here is where im at now... The IAC is not doin its thing, The IAC is brand new. The red wire is a good 12+ volts, KOEO and KOER. The ground is the problem... with key off, it is grounded, turn to KOEO there is no ground, also no ground with KOER. Digital volt meter never showed any ground, not even a flicker when key is on, even if i load the engine by letting clutch out in gear with break on, it just bogs down till it dies, dosnt try to save itsself . If i manualy jump the ground (grey wire) to a ground, the idle shoots up. So, my high idle is coused by what has to be vacumme leak, right? I guess i just missed it when i did the old propane and also starting fluid tests. But, what is cousing my computer to not give ground to IAC when key is on?