93 starts won't Idle

Okay here is the problem 93 Tauras wagon with 3.8L. The car will not start unless the throttle is cracked open roughly an 1/8. It runs fine as long as open, once you let off it stalls. Won't Idle. I checked for vacuum leaks and found the intake gasket bad mainly for coolant into the cylinder. Still the same idle issue. Replaced cap rotor, plugs and wires, still the samething. Also tried a new MAF sensor Any chance this is an IAC problem??? Or any other suggestions. I am at a loss?
Thanks

Sounds like an IAC issue, or too much carbon on the throttle plate. Pull the air intake hose from the throttle body and open the throttle plate fully. Using a good light, inspect the back side of the throttle plate for carbon build up, as well as the intake plenum after the throttle plate. If it is caked with black gunk, you will need to clean that off using throttle body cleaner intended for Ford's coated intakes.

If that doesn't fix your problem, or there is no obvious gunk, then you may want to try cleaning the IAC valve with throttle body cleaner. Also make sure the passages to the IAC are clean.

While you're at the parts store picking up the throttle body cleaner, pick up a bottle of fuel injector cleaner and dump the contents of the bottle into the gas tank.

-Rod

Okay. I pulled the IAC and flushed it with cleaner. Everything seems to be free. Still has the same problem. With the throttle cracked it will start, then I can let off the throttle but will not idle dies at 500 rpm. I also pulled the TPS and tried starting with it at about 1/4 "throttle". No difference.

Should the IAC plunger be normally open or closed? I did not throughly inspect the throttle plate is there any sort of air bleed hole that could be plugged?
thanks for the help.

There will be small air passages on each side of the throttle plate that allow air to flow to the IAC servo, through the servo valve, and then into the air intake on the back side of the throttle plate. These passages will need to be clean as well. I believe the normal position for the IAC is closed. When the car detects that the intake air is too cold, it opens the IAC depending on the temperature.

Do you have access to a scan tool with a data stream mode? It would be nice if you could see real time what temperature the car thinks the intake air is. Maybe the Intake Air Temperature (IAT) thinks the incoming air is warmer than it really is.

-Rod

I pulled the throttle body and thoroughly cleaned it. Replaced it and still the samething. I also checked the temp for the IAT seems to be correct reading 54F which is pretty close to the garage temp. The ETS also started at the same temp and rose up to 112F when I shut it off. What I did notice is the TPS doesn't seem to be changing. The TPS output stayed at 1.0 to 1.3 it would only rise slightly with 50% throttle. I would assume the voltage should go to at least 4.0volts output. the input shows 5.0 volts. I pulled the TPS and checked for any resistance between terminals and all are open circuits. I also checked them with the sensor rotated ~50%, same thing. Is it possible the it can run with out this sensor working at all??? accept for the "minor" idle issue???

Thanks again for your help, Davin

Yeah, the TPS sensor resistance/voltage should change linearly as you open the throttle. If it is not linear, or there are "dead" spots, you should change the sensor. Are the readings you're seeing as reported by the scan tool or by a multimeter connected at the sensor? If by the scan tool, do you know what the sampling rate is? You would have to move the throttle VERY slowly to see a change in the the TPS voltage if it is like most scan tools.

-Rod

I am not sure on the sampling rate. But what I did do is a just have the key on an monitor the TPS voltage and it only goes from 1.2 to 1.5 volts, basically looking for static numbers Idle to full travel. I just checked the sensor itself pushing 5 volt supply to it and the voltage output will go from 1 to 4.8 volts, and appears seamless. I will also trace with an O-scope but initially it appears it is fine.

Now I am questioning the wiring for damage. Will the "wiggle" test find anything like this?? I can't believe the car would run without the TPS signal being correct, especially not throwing a code. What else can I check?

Hmmm, that's an odd one. So when you bench test the TPS, it tests fine. On the car, the scan tool shows a 0.3 V range, or a meter shows that range? You mention there's a 5 volt input, but was that measured at the car's wiring, or on the bench? Since you have access to an oscilloscope, you probably understand, the TPS is just a potentiometer which sets up a voltage divider. Since you are getting a range of voltages back when the TPS is connected to the car, and a bench test shows the TPS is okay, I'd suspect, as you have, that you have a wiring issue to the sensor.

I'd suggest you use a decent DMM to monitor the voltage to the TPS. An o-scope is overkill here. Connect the red lead to the supply to the TPS by back probing the connector and the black lead to a good chassis ground. If you see 5 V, now connect the red lead to the signal line of the TPS, again by backprobing. Move the throttle and see if you get the expected range. If so, now move the black lead of the meter to the ground/return for the TPS and see if your voltage reading drops. If it does, you must have a dirty/bad ground/return connection somewhere between the TPS and ground.

If you don't see 5V between supply and the chassis ground, then I'd suspect a dirty connection between the TPS and the PCM, or possibly internal to the PCM.

I would expect your expectation to be correct, that if the signal is really that low to the TPS and the PCM is functioning properly, the CEL should illuminate. A bad TPS will probably not cause the engine to not run, but your responsiveness and fuel economy could be greatly effected.

-Rod

Yes the .3 volt range and a 5 volt supply is from the scan tool. On the bench it shows up to 1.2 to 4.8 volts output with a 5 volt input.

thanks for diagonis procedure I will check that tonight when I get home. I will post results by 10pm est.

thanks for your prompt and thorough responses, you have been a great help. Davin

Looks like you should expect to have a diagnostic trouble code (DTC) of 124 - TP sensor output is higher than expected, or a DTC 125 - TP sensor output is lower than expected. According to the service manual, these codes "were intended to detect in-range failures of the TP sensor. The PCM compares information from the MAF sensor, TP sensor, and fuel injection pulse width. If any one value appears to be out of line with the other two an in-range trouble code will be set."

The Throttle Position wire should be the gray/white wire, Vref is the brown/white wire, and signal return is gray/red.

-Rod

Well Crap!! I struck out completely. Evidently when I was watching the TPS Volts I did not let it catch up. Tonight everything checks out fine, still won't idle. The TPS measures good on the car with a DDM and with the scan tool. Scanner was not updating fast enough. Which is odd becuause on any of my GM's the change is there right now, must have a slower rate out of the computer.

The only code I have been able to get out of this is a 157. The haynes manual says it is a MAF sensor out of range. I checked the resistance in this and it is with in .1 ohm of a new part. Now I am lost.

Rod sorry for the wild goose chase on the TPS, I am positive I let it sit long enough for any lag to catch up. :disappoin

Here is the info that my Actron (9145?) scanner reads live. Info is while idling with my wife's steady foot on the throttle. I don't know where to go from here. HELP!!!

BOO/BPP = Off
Canst Purge = On
ECT (V) = 1.0
ECT *F = 162
Engine = 660
EVR% = 0
Fuel PW1 (ms) = 6.7 - 7.0
Fuel PW2 (ms) = 6.7 - 7.0
IAC % = 55
IAT (V) = 2.0
IAT (*F) = 117
Loop Status = Clsd
LT FTRM1 % = 0
LT FTRM2 % = 0
MAF (V) = .7
O2 Sen 1 (V) = 0.00
O2 Sen 2 (V) = .69 - .15
Spark * = 30
ST FTRM1 % = 2.7
ST FTRM2 % = 2.7
TOT *F = 71
TOT V = 3.0
TP Mode = P/T
TPS (V) = 1.0
VPWR (V) - 13.7
Vref = 5.0
Vss (MPH) = 0
Wot A/C off = off

Hmmm, the O2(1) voltage at 0 V is not good. Ideally this reading would float around 0.45 V, which is the threshhold between rich and lean fuel mixture. It should cross that threshhold quite often (O2CC or cross counts). That combined with your MAF code could be part of your problem. A reading of 0 on the O2 sensor would indicate to the computer that the air-fuel ratio is extremely lean, so the computer will tell the injectors to dump more fuel into the system. This could explain why the car won't idle, it is basically flooding itself out. When you open the throttle, you're letting more air in, so the mixture is leaning out somewhat. Verify that the O2 sensor on bank 1 is connected. I think bank one on your car will be the rear bank, nearest the firewall. Does the voltage for the O2 sensor change at all, or stay constantly at 0? If it changes when you blip the throttle, or changes very slowly, then replace the sensor. If it stays at 0 V, check for shorts in the wiring, etc.

This O2 sensor issue could be causing the MAF out of range code, or the MAF could be out of range, causing the O2 sensors to go bad. Do you have a K&N or similar oiled air filter? If so, you probably have a coating of air filter oil on the MAF sensor elements which could be causing the code as well as the rich condition. You can clean the elements if you have a steady hand, so chamois swabs, and some Isopropyl alcohol (NOT rubbing alcohol which is ~70% water).

-Rod

Here is the latest. I think we are on to something. I pulled both of the O2 sensor and replaced. The front one (sensor 2?) had a bad wire but was working, replaced anyway. The rear one (sensor 1?) was covered with black soot, also replaced. It finally manages to idle just barely at 450rpm. The code scanner still is not getting any voltage reading from the Sensor 1. I have looked over the wiring, as far as I can tell there is no visible damage. Any spot these are prone to abrasion?

I also ran the KOER test and I get a code 412 "cannot control RPM During Self test High rpm check". Does this mean anything to you??

When you say it won't idle, did you mean that the engine stops, or by it the engine stays running but runs rough. Seems like you guys know the complexities of the car. If all inputs to the module have been changed or were functioning well, then perhaps the module is malfunctioning.

Just a guess here on the code 412. Sounds like maybe the idle air control is not working. Do you happen to have a signal generator that can generate a 5-volt PWM signal? If so, I think you could probably bench test the IAC.

As for a spot that's prone to abrasion, I'm not that familiar with any particular spot, but then again I'm a hobbyist automotive tech, not a professional who sees a lot of Taurii on a daily basis. I owned a couple of Taurus SHO's, but never a "normal" Taurus.

-Rod

Well I was thinking the same with the IAC but I had a new one and it didn't seem to act any different. I just took it back to the parts store today.. I am only a hobbiest also so I know what you mean. I got it to idle by adjusting the set screw but I know this is not the fix. Is there a good way to check with a DMM the lead from the harness on the O2 sensor to check for a break???

DonSor: it will not start unless I apply the gas, it will start right up then but it will not idle, dies right out.

According to the service manual, the items that can cause the code 412 are:
-Open or shorted circuit
-Throttle linkage binding
-Improper idle airflow set
-Throttle body/ISC solenoid contamination
-Items external to Idle Speed Control system that could affect engine rpm.
-Damaged ISC solenoid
-Damaged processor.

Have you removed the processor from the car before, or are you comfortable removing it? If so, you could remove the processor and check for continuity between the processor and the O2 sensors. One check you could try before doing that is to disconnect one at a time and see how that affects the readings you get. For one, that will help you determine which sensor is in bank 1, and two, if a code would be set if the sensor wiring is open.

The wiring connector to the PCM unbolts from the upper firewall under the hood on the passenger side. The PCM will be removed from the inside after you open the glove box door completely and remove the one mounting bracket. The service manual shows that pin 94 is for the #2 O2 sensor, and it's labeled "Front." The wire color should be Red/black. Pin 74 is for the #1 O2 sensor, and that wire color should be gray/black. Pin 46 is the signal return for the O1 sensors, and it is a gray/red wire. Of the two remaining wires for the O2 sensors (heated), one is power with the key in "Run" and the other is ground.

-Rod

I did the check to see which O2 sensor gives me a problem and I have determined it is the Bank against the firewall (go figure). It is interesting that it does not throw a code with both sensors (or either one) unplugged completely. it acts exactly the same. I have the PCM disconnected now (funny you should recommend that) and will check for continuity to the pins. Should I assume a new harness if I find a bad wire? (thinking like as a repair shop). I will post back in an hour or so.

thanks Again.
Rod if you don't mind PM me your phone number.

Okay here is what I have so far. I pulled the main connector off the firewall retained with a 8mm bolt. Removing the shroud shows me the wire colors and the numbers. However this is only a 60 pin connector. Does the manual show some sort of offset/coorelation on the Pin numbering scheme?? Just so I can verify the pin location.

I did however find the wire colors you mentioned and on the front sensor #2 the red/black wire has connection to the sensor connector. What is the wire color for the signal on #2.

Sensor #1 the gray/black has no connection = BAD The Gray/red (signal) is Good.

Can I assume I could run a wire directly from the connector at the sensor up to the PCM connector and effectively Jump the bad wire? Or do I need to locate the bad spot in the wire? Is there anything inbetween the 2 connectors or just wire?
Thanks we are getting closer.

BTW do you think there could still be a problem with the IAC? If still have a couple hours to pick one up before the part store closes for the weekend. thanks

Okay here is what I have so far. I pulled the main connector off the firewall retained with a 8mm bolt. Removing the shroud shows me the wire colors and the numbers. However this is only a 60 pin connector. Does the manual show some sort of offset/coorelation on the Pin numbering scheme?? Just so I can verify the pin location.

I did however find the wire colors you mentioned and on the front sensor #2 the red/black wire has connection to the sensor connector. What is the wire color for the signal on #2.

Sensor #1 the gray/black has no connection = BAD The Gray/red (signal) is Good.

Can I assume I could run a wire directly from the connector at the sensor up to the PCM connector and effectively Jump the bad wire? Or do I need to locate the bad spot in the wire? Is there anything inbetween the 2 connectors or just wire?
Thanks we are getting closer.

Oops, I gave you the number from the wrong column in the wiring table. O2 #2 (front) signal wire is pin 43 (red/black), pin 44 (gray/light blue) is the signal wire for O2 #1 (rear). I guess I was tired when I typed the last message. Gray/black as I typed last message is the wrong wire color for this. The gray/black wire is for the transmission speed sensor, and should be in pin location 5. The sensor return is pin 46 (Gray/red).

If you do find a bad wire, ask me to double check the wire color and pinout again (although I did get a good night's sleep last night). If everything still matches up, then you should be able to run a jumper wire to see if that changes the idle. However, I would suggest following the original wire and trying to determine when the problem is. If something happened to cause this low current wire to open, chances are pretty good there are other wires in the harness that are or are about to open as well.

Sorry for the passing on some wrong info in my last post.

As for the ISC/IAC, you should probably hold off on that until you get the O2 sensor issue resolved.

-Rod

Can you tell me again what are the 2 Pins and colors for the #1 Sensor (Rear)?

Corrections: here is what I have.
Looking at the wires from the harness connector at the O2 sensor to the PCM connector.

Sensor #2 Front:
red/black wire continuity to #43
gray/red wire continuity to #5, #28, #46

Sensor #1 Rear:
gray/light blue wire continuity to #44
gray/red wire continuity to #5, #28, #46

I assume the gray/red wires are T'd in the harness some place. Are these a power or ground by chance?

It appears to me these maybe connected correctly in that case the PCM is questionable correct??

Pin 5 is for the Transmission Speed sensor (gray/black) and Pin 28 is for the Power Steering Pressure switch. Pin 46 is the return for the oxygen sensors (ground) and yes, the return line is common between the two O2 sensors. I'm not sure though why they would have continuity to the PSP though. The transmission speed sensor is probably essentially a DC motor/generator, and therefore that makes some sense as your "continuity" is probably small DC resistance through the coil of the motor. The PSP continuity makes sense after reading the description for the PSP, "With no power steering pressure applied the reference voltage is shunted to ground along the SIG RTN circuit."

Have you verified the remaining two wires to the O2 sensors for the heater? You should do that prior to condemning the PCM. Ford PCMs have a pretty high reliability. If your O2 sensor heater is not working, your O2 sensor will not work properly until it's up to temperature.

-Rod

argh!!
Both of the O2 have 12.46 volts across the other 2 wires and they physically get warmer with the key on. Assume this says the PCM is doing its job?? But still why no #1 O2 reading on the scanner. It seems a complete 0.00 reading should throw a code.

Help!!! I can't figure this crazy thing out!!!!

There a few options here that I can think of:

1) You can try to find someone with a known good loaner PCM for your car and see if that makes a difference.

2) You can backprobe the O2 sensor wires for the signal and return lines either at the sensor or at the PCM (preferably at the PCM) and see if the voltages reported on the scan tool agree with the voltages one from the sensor. You'll obviously need to have the PCM installed for this step.

3) You can remove the O2 sensor from the car and test it on the bench with a vice, a DMM, and a propane torch.

Since you've replaced the sensors recently and still no change in the readings of the O2 from the PCM, I'd suggest starting at the second option. Finding someone to help out with option 1 could be pretty tricky. If you find that the O2 sensor is reporting accurate voltages to the PCM, then your PCM seems like a likely suspect.

-Rod

What input voltage is the output voltage based on?? 5 volts? With just the key on and engine cold both sensors only have a 12volt supply. Seems as though one of the sensor pins should have a lower supply voltage.

What is the other pin# at the PCM for the #1 O2 sensor (Rear)??

Here is what I know today.

I back checked the o2 sensor outputs at both the sensor and the PCM. The front sensor (red/black wire) fluctuates like the scan tool reports, .25 to .8 volts. the rear sensor (gray/light blue) reads .9 to .8 with the voltmeter, scan tool still says 0.00. Since the rear is sending info to the PCM does it make sense that PCM is not getting it. The power is getting to the pin and the pins on the PCM look fine. Does the lack of fluctation in the output, .1 volts relative to the front, that the PCM is not adjusting fuel to this set of cylinders?

I will also try pinching the pin on the connector side to make sure the connection is being made to the PCM.

Just to cover another base I pulled the EGR and flushed with cleaner and pulled a vacuum on the diaphragm and it all looks okay and moves freely.

Lastly, what are your thoughts on a yard PCM vs a reman from Carquest??

Thanks for your continued support on this I will owe you a twelver when this is finally fixed. :iceslolan

Okay here is the last update for tonight.

I pulled the PCM connector and pinched the terminal tight to where the PCM pin should spread the pin open during installation. Basically the best thing I can do to ensure connection.

And ....... the same thing no Sensor 1 O2 output through the scan tool.

ARGH!!!!!

Let me know what the thoughts are on a new PCM.
IS the only Tauras out there that has had this type of problem????????

The O2 sensor actually generates a voltage based on the difference between the amount of oxygen in the reference air (outside the exhaust) and the oxygen in the exhaust stream. My understanding is it does not need a reference voltage. The sensor can generate as high as 1 Vdc. The 12Vdc supply voltage you are seeing is only for the sensor heater. An oxygen sensor is only accurate once it gets up to operating temperature. Early single wire sensors did not give readings for the first few minutes the car was running. This was one of the reasons the early computers would start out operating in "open loop" until the coolant temperature got up to some set temperature. At that time, the computer would transition to "closed loop" and begin to use sensor feedback to control air/fuel ratios and other parameters.

Since you are seeing a voltage at the PCM, but the scan tool is not reporting it, that does make the PCM suspect. One thing you should try is to disconnect the rear O2 sensor and see if the voltage between pin 44 and pin 46 remains at 0.9 Vdc. If so, the voltage you are seeing is coming from the PCM rather than from the O2 sensor. That again would lead to a suspect PCM. If the voltage drops to zero, and the sensor is actually putting out a constant 0.9 V, you either have a bad sensor or a VERY rich mixture on the rear bank of cylinders.

As far as picking up a used PCM from a scrap yard, I wouldn't be too concerned about that, depending on the price difference from a reman unit. Ford PCMs have been rather robust.

-Rod

Still searching for the problem.. I picked up a "new" computer from the yard plugged it in and it still does the samething. Still 0.00v output on the scan tool. I also replaced the coolant temp sensor and still no change.

as a side note, This thing has also generated a slight whistle (sounds like a vacuum leak) at cracked throttle, that is loud enough to clearly hear going down the road. I used a hose to try to pin point the sound and it is around the #4 injector. So I pulled the intake off and replaced the orings at the manifold. No change. I looked the upper and lower manifold over closely but I don't see any cracks and I am positive the new lower intake gasket is sealing. I have sprayed brake klean, carb cleaner and propane and can't pinpoint the leak any better.

Anyone else had any whistling issues like this?

This thing sure has me guessing at this point????????????

Wow, I'm going to be very interested to learn what you finally find to get this car fixed! Your car has some strange issues!

-Rod