Unplug Idle air control valve and engine dies (2.9L V6), Normal or bad valve?

[wildbill23c]

The IAC didn't completely correct my problem, and upon further testing of sensors I found that my TPS is bad, I unhooked it this evening and it ran and drove great for over an hour. Plugged the TPS back in and right back to the same power loss, bucking, no throttle, etc. I ordered a replacement TPS from Rock Auto (really should have stock in their company as much as I've ordered there lately LOL).

Where can I locate a Tachometer to temporarily install to properly set the idle speed? My truck is tachless LOL. I don't need a permanent install just one I can look at to adjust the idle speed to where its supposed to be...it wants to idle extremely low when the TPS is connected so I think once I get the new one installed I may need to adjust the idle.

 

[RonD]

I used to have a spark tachometer, inductive clamp on any spark plug wire and battery clamps for power, like a timing light but showed RPMs

Had 1, 4, 6 and 8 cylinder settings

But just did a quick look and didn't see anything like that sold any more

 

[wildbill23c]

I used to have a spark tachometer, inductive clamp on any spark plug wire and battery clamps for power, like a timing light but showed RPMs

Had 1, 4, 6 and 8 cylinder settings

But just did a quick look and didn't see anything like that sold any more

Why is it the automatic equipped trucks seem to be more common to have a tach than a manual equipped truck where you'd think a tach would be much more helpful...my Bronco 2 has a tach but its an automatic, and so were the 2 Rangers I found at the pick a part last week...yet my Ranger has no tach and has a 5 speed LOL. A bit backwards I'd think.

I'll have to lookup the idle specs for the manual transmission, but it was idling what seemed to be about 1200-1500RPM with the TPS disconnected, I turned the idle screw a bit to lower the idle to what sounded more reasonable then when the TPS is connected it will idle down to the point where I'm sure it would have died if I hadn't turned it back up a bit LOL. Oh well, I'll wait till I get the new TPS then go from there.

 

[alwaysFlOoReD]

The TPS doesn't have an idle screw. The IAC is what controls the idle.

 

[RonD]

Yes, +1 ^^^^

What you are adjusting is the anti-diesel screw

To set that, warm up the engine fully, 10minutes at least
Let it idle and then unplug the IAC Valve
Idle should drop to about 500rpm, barely running, if so then all is well
If not, THEN adjust the anti-diesel screw until engine is at 500 or barely running

Now plug IAC Valve back in and RPMs should go up to "target idle", which is the preset idle the computer has in memory for fully warmed up engine
About 625 for manual, 750 for automatic

You do not need to unplug the TPS, the TPS is only used to give the computer a "heads up" when you press on the gas pedal, so you get instant acceleration and when you let off the gas pedal computer can shut off injectors to save fuel until RPMs drop below about 1,200 then it restarts them at idle level

It is also used for WOT(wide open throttle), when computer see this it will ignore O2 sensors and just dump in the fuel for best power, MPG is off the table, lol

After doing the anti-diesel screw adjustment, you can test TPS voltage to make sure its still within parameters
Use a sewing needle to pierce the TPS's center wire
Set volt meter to DC volts
Turn key on
Ground the meter and test center wire, should be .69-.99v under 1 volt
Now open throttle all the way, WOT, test center wire, should be 4.5-4.9volts

If either is out of range adjust TPS, it should have slotted holes

 

[wildbill23c]

Installed a new TPS, and it still acts like its going to stall when accelerating on the highway. It runs great with the TPS disconnected though.

 

[wildbill23c]

The TPS doesn't have an idle screw. The IAC is what controls the idle.

Idle adjustment is on the accelerator linkage bracket, turning the screw in or out raises or lowers the idle.

 

[alwaysFlOoReD]

Idle adjustment is on the accelerator linkage bracket, turning the screw in or out raises or lowers the idle.

Not as far as I know.
Read RonDs post below my last post.

 

[RonD]

Fuel injected engines can't use an idle screw, there are no "Idler Jets"

I would say your TPS circuit in the computer is bad
TPS has nothing to do with idle directly
It is used to give the computer a "heads up" when you "step on the gas", so it can change spark timing and add extra fuel, same as vacuum advance and accelerator pump did for carburetor engines.

Without the change in spark timing and added fuel you WILL get a hesitation on acceleration, MAP/MAF sensors just don't react fast enough to the throttle opening on their own, which is why a TPS is needed

Idle is set by the computer using the IAC Valve, so the "screw" needs to be set BELOW warm engine idle level, i.e. set so engine idles at about 500rpm warm with IAC Valve unplugged

TPS should have 5volts on top wire and just under 1 volt on center wire, key on engine off
Then 4.5volts on center wire with throttle wide open
Lower wire is a ground

TPS center wire voltage is a "learned" voltage, so when you change a TPS you should have battery disconnected while doing the swap, 5+ minutes, then when you reconnect the battery the computer will re-learn the TPS and also IAC Valve and MAP and O2s

 

[wildbill23c]

Fuel injected engines can't use an idle screw, there are no "Idler Jets"

I would say your TPS circuit in the computer is bad
TPS has nothing to do with idle directly
It is used to give the computer a "heads up" when you "step on the gas", so it can change spark timing and add extra fuel, same as vacuum advance and accelerator pump did for carburetor engines.

Without the change in spark timing and added fuel you WILL get a hesitation on acceleration, MAP/MAF sensors just don't react fast enough to the throttle opening on their own, which is why a TPS is needed

Idle is set by the computer using the IAC Valve, so the "screw" needs to be set BELOW warm engine idle level, i.e. set so engine idles at about 500rpm warm with IAC Valve unplugged

TPS should have 5volts on top wire and just under 1 volt on center wire, key on engine off
Then 4.5volts on center wire with throttle wide open
Lower wire is a ground

TPS center wire voltage is a "learned" voltage, so when you change a TPS you should have battery disconnected while doing the swap, 5+ minutes, then when you reconnect the battery the computer will re-learn the TPS and also IAC Valve and MAP and O2s

So is the screw I am referring to the screw you were calling the anti-diesel screw? That screw does in fact control idle though, if you turn it clockwise it raises the idle by pushing the throttle linkage back thus opening the throttle plate.

So if that TPS is supposed to the timing upon acceleration, it sure isn't doing anything because it runs and drives great without any hesitation at all with the TPS disconnected.

I'm thinking what you are thinking though, that the particular function in the ECM is bad...the only thing that the TPS is doing is causing a horrible stumble/stall symptoms upon trying to accelerate at highway speeds that a working TPS should be preventing not causing LOL.

I guess I'll look into a replacement ECM for it...I guess the ECM would be needed for a manual transmission as I believe they are programmed different for an auto/manual.

I didn't disconnect the battery, but I highly doubt in my case it would have made any difference, but I'll try and disconnect it tomorrow as I'm working on some other things. The battery has been disconnected enough times that if it were a learning issue it would have been corrected by now, it runs and drives great anytime you disconnect the TPS, I would never have thought about the ECM being the culprit though.

Thank you for the great education about these things...this is why I keep an open mind and come over here to this forum, I know you guys know your stuff...sorry for the above statements & questions, I'm not questioning your experience, just trying to figure out why it does what its doing that it shouldn't be doing according to your given information it should drive worse with the TPS disconnected, but its doing the opposite LOL...is my truck backwards? HAHA!!

I feel as though I'm getting closer to it being fixed. I believe a replacement ECU is about $150... not sure I would trust a junk yard one? Or should I? But wouldn't I need one from an 87? So year, and transmission would have to be the same?

Guess Rock Auto will be receiving another order soon LOL.

 

[RonD]

I would check voltages at TPS first, could be wiring issue not computer issue

Yes, Ford renamed the idle screw as the anti-diesel screw so people didn't try to use it to change idle RPMs, with either name the screw opens/closes throttle to let in more or less air, which, with fuel injection, is the job of the IAC Valve so computer can set correct air:fuel mix for idling, and also raise RPMs in Choke Mode, since there is no step Cam like a carb had on the "idle screw"
So anti-diesel screw no idle screws on fuel injected engines


Also on the inner fender there is a starter "relay" not a starter solenoid, and they are called Core Plugs, not Freeze Plugs, lol

 

[wildbill23c]

I would check voltages at TPS first, could be wiring issue not computer issue

Yes, Ford renamed the idle screw as the anti-diesel screw so people didn't try to use it to change idle RPMs, with either name the screw opens/closes throttle to let in more or less air, which, with fuel injection, is the job of the IAC Valve so computer can set correct air:fuel mix for idling, and also raise RPMs in Choke Mode, since there is no step Cam like a carb had on the "idle screw"
So anti-diesel screw no idle screws on fuel injected engines


Also on the inner fender there is a starter "relay" not a starter solenoid, and they are called Core Plugs, not Freeze Plugs, lol

I have a starter solenoid its not a relay LOL.

I checked voltage at the TPS which led me to the TPS being bad, and replacing it, I was wondering about a potential bad wire too, I'll check into it further this weekend and hook the meter up and jiggle the wiring around and see what happens. The voltage at the power side of the TPS plug should be about 5V if I'm not mistaken? Then the middle wire should be the one that varies when you accelerate, the other wire is ground I assume....So I'll do more digging for sure. Looked like the TPS had been replaced before it wasn't the factory TPS. So I wonder if this issue was why the truck was sold in the first place, most likely was LOL.

The truck starts up without the TPS but idles weird, and for the first few minutes won't accelerate at all, once it warms up it drives great LOL. The only thing is I need it to run properly all the time with everything hooked up like its supposed to be LOL.


Thanks again for your help.

 

[RonD]

A solenoid causes mechanical movement, a relay causes an electrical connection
In the early days there was no "relay", just solenoid, because it does cause mechanical movement of an "arm" when it pulls it down to close the circuit, but when they became more common in circuits these electric switches were named relays, and solenoids became the name of mechanical movement devices

On the starter motor itself there can be a solenoid that pushes/pulls out the starter gear to mesh with ring gear
On the inner fender there is a relay that sends 12volts to starter motor

In later years they combined relay and solenoid and both are on the starter motor

TPS info here: http://www.fuelinjectedford.com/page30.html

 

[wildbill23c]

I found that link in another thread regarding a TPS issue, that website is extremely helpful, thank you.

I'll definitely be doing more testing when the weather warms up. I did drive the truck to work this morning, it did fine after a few minutes of idling to warm up. Can't wait to get the rest of this issue taken care of and things hooked up properly. I'll be going through the wiring too and make sure there isn't any damage there, and go from there.

First things first though, I'm going to disconnect the battery as I had not done that prior to replacing the TPS, I highly doubt it'll make any difference but at least it'll give the ECU a good starting point I'd think.

 

[wildbill23c]

I disconnected the battery cable this morning, plugged the TPS back in, let it sit for about 15 minutes while I was finishing up a light bulb replacement in another vehicle. Hooked up the battery, took it out for a test drive, seems to be working now. Woohoo, finally. Just something about these older Rangers I just like them.