Calling Jstas and all car gurus

audiobliss

A friend has a 2006 Ford Explorer V6. The check engine light's been coming on periodically (about once a week?) for the last three months or so. When it comes on and stays on, the vehicle doe not perform well at all. Meaning, the throttle pedal does not work linearly, the vehicle has a very delayed, jerky response to throttle input, and it just kind of bucks in hesitation. Whenever this happens, pulling over, shutting down, and restarting always fixes the issue. Going home to warmer weather over Christmas break last year it didn't exhibit this problem at all until returning to school and cooler weather.

So, we took it down to AutoZone and had them pull the codes on it to get a better idea of what's going on.

Trobleshooting P2135
OEM Brand: Ford

Definition
Electronic throttle control (ETC) position sensor
A/B voltage correlation

Explanation
ECM detected TP 1 and TP 2 do not agree

Probable cause
1. - Failed Throttle Position (TP) sensor
2. - Open or short circuit condition

I'm not sure exactly how I'm supposed to respond to that, but with modern drive by wire systems, I don't like the idea of there being conflicting information regarding throttle position. So far the problem has just been hesitation and jerky driving. But if the vehicle's not sure what the throttle position is, is it not just as likely that it will one day go full throttle when it's acting up? Obviously it's not just as likely as it hasn't happened yet. And I'm not sure what kind of fail safes are built-in with drive by wire systems, but surely there is something in place to prevent my concern from becoming reality. But not knowing a lot about such systems, it is still a concern.

Up to this point I have done very little research on the problem. But my current understanding is it could be the TP sensor (~$60 fix), or some receiving unit (ECM? much more expensive, I'm assuming), or a short. I even read about the possibility of it just being a loosely mounted TP sensor. What is the most likely cause of this error? What is the best way to narrow it down/approach fixing it? If it's not something that's ever going to get worse, ie it will always just be jerky until a restart, then the owner might decide that it's not worth even $60 to fix.

Any light you could shine on this issue would be very much appreciated! Thanks!

Jstas

Throttle position sensor.

Replace it.

Check the wires going to it as well as the connector condition. If they are bad as well, replace them.

I doubt it's a loose sensor because it's a voltage correlation error. The only way a loose connector could affect that is if the mount was the ground point. That's unlikely in a throttle position sensor because it's variable so the sensor itself cannot be the ground.

Oh and it'll get worse. But fail state is an open circuit so failure is not an open throttle.

Stop wringing your hands over it and do the obvious. Replace the sensor. It's going to affect more than just driveability. It affects fuel mileage and the computer will always want to run in limp-home mode which is bad for the emissions systems because it gets flooded with raw fuel and fouls things like O2 sensors and slags catalytic converters.

exalted512

audiobliss wrote: »

A friend has a Ford

problem found

But +1 to what John said. Over time, its going to make matters a lot worse and fuel economy can suffer as well, as mentioned.

-Cody

sucks2beme

If you get off the hook for only $60, go for it.
Always start with the easy stuff. Just make sure to look around for
anything else different. Loose, dirty, burned, pinched, you name it.
This sounds like a 90% fix. Most of the time you don't get a meaningfull
code.

nadams

I could be very wrong... but I didn't think the '06 explorers were drive-by-wire. Either way, just replace the sensor, like everyone else said.

Jstas

nadams wrote: »

I could be very wrong... but I didn't think the '06 explorers were drive-by-wire. Either way, just replace the sensor, like everyone else said.

I doubt they are. I'll have to check ALLDATA when I get home to make sure but I really doubt they are.

All fuel injected cars with modern electronic fuel injection have a throttle position sensor. Whether they have a cable operated throttle or a servo operated throttle. It doesn't control the throttle at all. It just gives a voltage value that corresponds with a known throttle position. Some of them have the sensor in the throttle control itself. Especially if it is a "drive by wire" system. If the sensor is returning a voltage outside that range or a voltage that doesn't jive with the amount of exhaust emissions the emissions system is saying is in the exhaust then, it's faulty. The poor running comes from the fact that the computer has no clue how much air is actually getting in to the engine so it deliberately runs rich to save itself. It stumbles when the amount of fuel in the combustion chamber is so great that it actually quenches the flame and will not burn because there is not enough oxygen present to ignite the fuel let alone burn it.

The only way the fuel gets out at that point is either pumped out through the exhaust valve or it gets blown past the piston rings in to the crankcase. Both scenarios are very bad. Gasoline is a solvent and dilutes the oil, causes it to separate and destroys viscosity. The oil doesn't lubricate at the point and you risk permanent damage and catastrophic bearing failure if you continue to run that compromised oil.

If it goes through the exhaust, it will foul the O2 sensors with soot and varnish. They will not heat up properly and will not return a proper value which further exacerbates the limp-home mode condition. This pumps more raw fuel in to the exhaust if you can even get it to run. That raw fuel pools in the catalytic converters and does two things. It reduces the flow of the exhaust through the converter. This causes exhaust to back up and build pressure which in turn makes the engine work harder and use more fuel. As it's building pressure, it's also building heat, the second problem. That heat causes the fuel to smolder and it can actually start to melt the catalyst in the catalytic converter. This is called slagging. What happens then is that the molten catalyst starts to exit the vehicle in chunks through the exhaust system. The heat is intense, to the point where it can set fire to the car. It's not a good thing at all.

$60 to fix a TPS. It's odd that it would fail on a 5 year old car but it's possible.

If it is replaced and there is still rough running/idling then you need to check the Idle Air Control Valve. It won't necessarily blow a code but if you pull it off and look inside the little valve body, check if it's all gunked up with soot. If so, you should replace that too. Unfortunately it'll be another $70 or so and you really can't clean them. Well, you can but it only works for a short while until it breaks again. A replacement is the better alternative.

audiobliss

Jstas, thanks so much for the wealth of information. It's very interesting and appreciated.

In such systems as described in your post, the TPS is the computer's only method of reading how much air is getting into the engine? Are O2 sensors always downstream of the engine? Is there no MAF sensor? I'm treading on thin ice here, mentioning things I barely understand, but it's my understanding that MAF sensors report how much air is coming through the intake. Is that incorrect, or just yesterday's technology? I know speed density systems used to do the same as MAF sensors, but I could be wrong as to what that is. Getting a little side-tracked, but in the pursuit of knowledge, how do MAF sensors and the Speed Density system of old differ in their method? A friend explained to me that MAF sensors heat up as air passes over an element, the hotter it gets indicating more air. How does that differ from a SD system's operation?

What is the function of an IAC Valve, and how could it be contributing to this issue?

I looked at RockAuto and TPS's are all about $60 there, so I'd be just as well off getting that from AutoZone. However, IAC Valves are only about $40 from RockAuto, so that might would end up being a better option if they're more at AutoZone if the TPS doesn't fix it.

Also, what is the role of the warmer and cooler climates in this equation? Does that really play into the scenario, or are we ruling that out as coincidence?


Thanks so much for the info Jstas. I always love reading your posts relating to cars. On one hand it's depressing to be reminded of how ignorant I am, but I always learn a great deal!

nadams

The MAF (Mass Airflow Sensor) is what reads how much air is getting pulled into the engine. The TPS (Throttle Position Sensor) only monitors throttle position, which the computer compares to the other readings it's getting at any one time. The IAC (Idle Air Control) is what keeps your vehicle idling at a constant rate. If your IAC valve sticks or stops working, the vehicle will stall.

audiobliss

So the IAC is like a MAF, but only for low airflow situations? I guess they're calibrated for different situations? If it's hesitating at or just off-idle, IAC...if it's only under throttle it's MAF...? If the problem manifested itself under both conditions, would there be another culprit?

Kinda venturing into the hypothetical here...

kawizx9r

Replace sensor as recommended.

Had the same problem in my Focus awhile back, replaced with an OEM sensor. Sure it's a bit more, but I did it because aftermarket sensors don't work too well on both Chrysler and Ford vehicles (in my personal experience).

sucks2beme

audiobliss wrote: »

So the IAC is like a MAF, but only for low airflow situations? I guess they're calibrated for different situations? If it's hesitating at or just off-idle, IAC...if it's only under throttle it's MAF...? If the problem manifested itself under both conditions, would there be another culprit?

Kinda venturing into the hypothetical here...

IAC is just a air opening at stop. The throttle plate closes, and the IAC allows the right amount of air through to idle. I guess it's more emissions friendly than just cracking open the throttle plate, like in the old days.
Start with the TPS, and see what happens.

audiobliss

sucks2beme wrote: »

IAC is just a air opening at stop. The throttle plate closes, and the IAC allows the right amount of air through to idle. I guess it's more emissions friendly than just cracking open the throttle plate, like in the old days.
Start with the TPS, and see what happens.

Ok, that makes perfect sense. Thanks!

Jstas

nadams wrote: »

The MAF (Mass Airflow Sensor) is what reads how much air is getting pulled into the engine. The TPS (Throttle Position Sensor) only monitors throttle position, which the computer compares to the other readings it's getting at any one time. The IAC (Idle Air Control) is what keeps your vehicle idling at a constant rate. If your IAC valve sticks or stops working, the vehicle will stall.

It's not as simple as that.

There are several different kinds of flow meters. The one you are describing measures density.

The vane (flap) type air flow meters (Bosch L-Jetronic and early Motronic EFI systems or Hitachi) actually measure air volume, whereas the later "hot wire" and "hot film" air mass meters measure speed of air flow.

It measures density by determining the voltage needed to heat the wire to a certain temperature. The more voltage it needs to heat that wire, the more airflow is running through the meter. It determines this because higher levels of airflow will cool that wire more than lower levels. If it has to ramp up voltage to reach equilibrium to where it stabilizes the temp of that wire then it knows the airflow is higher. So if you have a known size of the MAF and you have a known CFM rate of that MAF, you can determine pretty accurately the volume of air flowing through that MAF with this method. It allows for density because more dense air will have a greater cooling effect than air of a lesser density.

However, that's not enough alone to be able to meter fuel. Most systems have an Intake Air Temperature sensor as well. By knowing what the density of air is at a certain temperature, the computer can use the MAF info and the IAT info to not only determine density but volume as well. The ECU then refers to a pre-programmed table to determine what pulse width with which to modulate the fuel injectors. However, some systems do not have an IAT and use a MAP sensor instead. It measures absolute pressure in the manifold directly rather than calculating it. It's typically used with speed-density systems but some odd MAF systems use both sensors, typically boosted engines might have a MAP and a MAF. It's rare to see them together though. Still though, some systems do not have an IAT at all and use a multi-stage O2 sensor system to determine what the air flow coming in is by measuring the amount of O2 in the exhaust. Yet still, some MAF sensors include a temperature sensor in the MAF itself to adjust for intake air temps so the output signal isn't affected.

Anyway, a TPS does more than just read the position of the throttle in a MAF system. The ECU will use the data from the MAF and IAT as well as the O2 sensors to determine airflow and volume as well as air/fuel ratios. It uses the info from the TPS to not only determine the user input to the system for what the throttle position is but with modern ECUs, the timing advance and fuel injection timing is determined electronically. Hence the term "Electronic fuel injection". Mechanical fuel injection uses a cam to operate a lever that opens and closes and injector. Pressure is made the same way, by fuel pump and fuel pressure regulators. Just like a hose nozzle on a garden hose, the fuel is always there, the injector is just a tap on that high pressure fuel source with a patterned spray nozzle to achieve the desire result.

An Idle Air Control valve is just that, a valve. The ECU determines idle speed by adjusting the IAC valve to allow airflow when the throttle body is closed. It's a butterfly or slide valve that is controlled by a motor and adjusted by the ECU. There is no sensor on it, the ECU adjusts it by applying a voltage within a preset value range. If it applies a voltage and is expecting a certain amount of air flow and adjusts fuel and timing for that expected airflow, it works. But if the valve sticks or fails, the idle becomes rough, the engine can be hard to start or it won't start at all. This happens because the valve may have the proper voltage applied but it is not providing enough energy to create enough force to open the valve to where it's supposed to be. When that happens, the ECU is giving the proper spark and fuel for the expected airflow but getting something less. Therefore the engine stumbles and stalls. O2 sensor info is typically not queried in the idle mode because idling systems are typically run in a similar loop to that of a speed-density system. If you have this problem over a period of time, the coil in the motor or linear inductor burns out and even if the obstruction is cleaned and cleared, the coil won't be strong enough for normal operation anyway. Therefore replacement is in order.

Speed density is different from MAF because speed density uses a table of values to determine Volumetric efficiency.

Speed Density systems accept input from sensors that measure engine speed (in rpm) and load (manifold vacuum in kPa), then the computer calculates airflow requirements by referring to a preprogrammed lookup table, a map of thousands of values that equates to the engine's volumetric efficiency (VE) under varying conditions of throttle position and engine speed. Engine rpm is provided via a tach signal, while vacuum is transmitted via an intake manifold-mounted Manifold Air Pressure (MAP) sensor. Since air density changes with air temperature, an intake manifold-mounted sensor is also used.

It still uses a TPS but only uses it for throttle position in most cases. Ignition timing is typically done with vacuum advance instead of electronic. Speed density is not as adaptive to environmental conditions and not as accurate in it's metering of fuel. Often times, if multi-point injection is used instead of throttle body injection, speed density employs batch fire where an entire bank of injectors is fired whenever one piston in the bank requires fuel in the combustion process. Most GM cars with multi-point fuel injection from the 80's and 90's operate this way. (Think GM corporate 4 cylinder and 2.8-3.4L V6's and LT1s) Speed density is also not as efficient and sometimes even a carb is more efficient.

Car Craft has a very good article on Fuel Injection systems: http://www.carcraft.com/techarticles/electronic_fuel_injection/index.html

Jstas

audiobliss wrote: »

Also, what is the role of the warmer and cooler climates in this equation? Does that really play into the scenario, or are we ruling that out as coincidence?

Nothing. It may idle rough when you first start it but it won't be stuttering and stumbling and trying to stay running. It might shake a bit or have a high idle until the engine temps come up and diagnostics are done. But once the engine reaches operating temperatures and the thermostat is open, outside temps don't affect basic running parameters. The ECM adjusts for them accordingly.

It's not a like a carb where you have to swap jets if the temperatures drop 15 degrees or the humidity jumps 20%.


Oh and stop kissin' my ****. You don't have to placate me and call me out by name. Ask your questions, if I know the answer, I'll post. So will everyone else. No need to sit here and stroke my ego. It just pisses me off and makes me not want to to help.

ben62670

So John what is a Holley 670 ProJection? I have one for my 68 Bronco 302. Sorry for the derail.
Ben

thebluemonkey

Im a big supporter of checking all the wires leading to sencers and switches> My cel came on on my grand cherokee and it was just the wire that was bad replaced the bad wire reset the computer and it was gone.

Jstas

ben62670 wrote: »

So John what is a Holley 670 ProJection? I have one for my 68 Bronco 302. Sorry for the derail.
Ben

I really have no idea.

http://www.holley.com/502-20S.asp

Judging by the description in the owner's manual, it's probably speed density. Or at least a modified version of speed density.