Idle air control valve issues

THESPYDAYOTA

MEMBER
2001 CHEVROLET MALIBU
3.1L
6 CYL
2WD
AUTOMATIC
104,592 MILES

This is a list of the new parts I have recently installed in this vehicle for reliability and improved performance: Coolant reservoir, coolant level sensor, coolant temperature sensor, upper and lower radiator hoses, radiator, thermostat, coolant flush, new coolant (dexcool - vehicle specified), water pump, water pump pulley, serpentine belt, idler pulley, tensioner assembly, idle air control sensor, idle air control valve, mass air flow sensor, throttle position sensor, canister purge solenoid, EGT valve, spark plugs, spark plug wires, coil packs, upstream o2 sensor. These parts were ordered between Advance Auto and O'Reillys. I had vehicle specific specs in the system so once I clicked to order a part it said Exact fit for your 2001 Chevrolet Malibu LS. One of the last things I changed was the upstream o2 sensor and by the next day I immediately noticed that whenever the coolant level lowered in the reservoir from cooling off from driving the night before, it is leaving a light colored residue that resembles oil in the reservoir which I have not noticed before and I have had this brand new reservoir for a few weeks and have been keeping my eyes on it as well as leaks. The film is the same orangish color of the Dexcool. I am not sure if that is a problem or not, but I wanted to point that out. There is no overheating or coolant leaks since all the major upgrades with the cooling system. The problem did not start until after I begin replacing sensors around the intake system. The vehicle cranks and immediately idles off. Sometimes but, barely, will it stay on. I have no issues driving and coming to a stop as well as running my A/C or heat (It is summer but there have been some random cooler nights). The next issue did not begin until after changing out the upstream o2 sensor. Only but not every time in park will the idle jump and fluctuate between 500 and around 15 to 2000 rpm's then eventually idle off. I cannot figure out for the life of me what I have possibly done wrong. I took the car to Advance and it threw four codes: EGR valve, gas, canister purge solenoid, and IAC valve. With the car running the guy working at Advance unplugged the IAC Valve and immediate no idle issues. He told me that the IAC Valve was failing. He cleared out the code and the engine light remained off. He plugged it back in and I drove home. The engine light never came back on but, when I got home and parked it before cutting it off, the idle began jumping again. Since the IAC Valve was not even a month old, I took it back and warrantied it out. Put the new one on and not even five seconds after cranking the engine light came back on. Took the car to O'Reilly and the same four codes came up as well as the erratic idling. I think I understand the process of resetting and relearning the computers. I take both battery cables off for about ten minutes, I have tried putting the car in drive with the emergency brakes on for two ten minute periods, I have read where you hold the gas for five minutes around 3000 rpm's until the car gets to normal operating temperatures, and I have attempted to do a road to highway back to road drive cycle, but I keep getting the same results after every time over and over again. It cranks and immediately idles off unless I lightly put my foot on the gas for a few seconds as well as in park, especially after having A/C on and cutting off the A/C before cutting off the car, it idles between 500 and 15 to 2000 rpm's several times, then idles off. The air filter is clean and I have cleaned the carbon build up around the butterfly valve in the intake manifold. With all these new parts, either I am not properly retraining my PCM and ECM to relearn the new parts or they are either themselves going bad. I have read about retraining a new idle air control valve and I thought I was doing it with the different ways of starting up the vehicle after having the battery disconnected, but obviously I am not doing something right. Please help. Thanks. Also, should I attempt the IAC valve relearn process as shown in the picture that I have posted or does this even sound like the source of the problem?

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5 Replies

CARADIODOC

MECHANIC
33,910 POSTS

To erase diagnostic fault codes yourself, only remove the negative battery cable, not both. You need both cables for the electrical system to work, so removing just one cable is all that is needed. It is customary to remove the negative cable because if the wrench hits a metal part of the body at the same time, there will not be any sparks.

The engine computer takes care of relearning any new sensors. All those steps you listed for trying to teach something to the computer had my head spinning. I have never heard of most of them. The only one I know for sure about is relearning "minimum throttle" on Chrysler products. The procedure is real involved. You are to drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals. That is it for relearns that you initiate. Everything else is easier because you are not involved. The instructions you posted are for the one in a hundred cars that might concern a customer, but almost all relearns are handled by the computer, and only a few take more than few seconds. In the majority of cases, there is nothing for you to do, and there is nothing you can do.

As a point of interest, what you are referring to as the idle speed sensor is not a sensor at all, and it is the same part used on Chrysler engines. That is a "stepper" motor that is controlled by the engine computer. Stepper motors do not spin like regular motors do. They have four coils that are pulsed with varying voltages and polarities to place the armature in a specific orientation. As that armature rotates, it is attached to a threaded shaft that extends or retracts a pintle valve. That valve opens an air passage around the throttle blade. At the same time it does that, the computer holds the injectors open for shorter or longer periods of time during each pulse. Adjusting air and fuel is how it controls idle speed. There is no such thing as an idle speed sensor. The computer knows engine speed because it knows how many times it is firing an injector and an ignition coil pack.

When idle speed is erratic, you have to look at the inputs the computer is looking at to calculate the idle speed it wants to see. The variable with the biggest say in idle speed is the coolant temperature. Except for a huge failure problem on early 1990's Ford engines, it is almost unheard of for a temperature sensor to fail because there is just one part inside them. It is common however to have corrosion on the connector terminals. That will add resistance to the circuit and make the computer think the coolant is cooler than it really is.

Basically, all you can do is observe sensor readings on a scanner and figure out if they look right. The computer even does most of that for you, then sets a diagnostic fault code when it detects a problem. There are plenty of conditions where a sensor reading is wrong, but not bad enough to be detected. Those are the ones that you have to go by the symptoms and determine which sensor reading is wrong, and why. It could be a failing sensor or it could be a good sensor is detecting an unacceptable condition.

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Monday, July 10th, 2017 AT 9:11 PM

THESPYDAYOTA

MEMBER
12 POSTS

I appreciate you for you taking the time to explain so much. What I am calling what I think is an IAC sensor is right before the IAC valve which sits above the TPS sensor which all are before the MAF sensor. The IAC sensor or should I be saying temperature sensor which I am not talking about the coolant temperature sensor plugs into the rubber part of the manifold before what I call or know as the butterfly section which the rubber part of the manifold I am talking about is right after the MAF Sensor. It is just not making sense that after replacing the old parts (temperature control sensor, mass air flow sensor, idle air control valve, EGR valve, canister purge solenoid, throttle position sensor, and idle air temperature control sensor) that I am still having idling issues. Any further help or info. Is much appreciated.

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Tuesday, July 11th, 2017 AT 12:05 AM

CARADIODOC

MECHANIC
33,910 POSTS

You are going to have to use a scanner to see what the engine computer is responding to. If the idle speed motor is being opened very little, a vacuum leak is a good suspect. Besides trying to correct for the increased engine speed, the clue is often that idle speed varies up and down for no apparent reason. Besides the leaking vacuum hoses and intake manifold gaskets, look at the fresh air tube between the mass air flow sensor and throttle body. There cannot be any cracks, loose hose clamps, or other leaks in that hose. If any air sneaks in there without going through the mass air flow sensor, it will not get measured and no fuel will be included in the calculations to go with it. That can result in an excessively-lean condition the computer is trying to correct for.

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Wednesday, July 12th, 2017 AT 12:47 AM

THESPYDAYOTA

MEMBER
12 POSTS

Ok. I think I've solved the issue. What I was calling an iac temperature sensor is simply an air temperature sensor that plugs into the rubber hose of the intake right after the maf sensor.

I changed out the tps and the car runs just fine. I noticed with the old tps that was actually new, when I positioned the sensor on the the knob that sticks out (I apologize, but I do not know the correct terminology), I had to turn the sensor before it actually seated in the position to tighten it in place with the screws. But with the new one, it slid onto that knob and immediately seated in the position to tighten it with screws without having to turn the sensor.

It seems as if someone may have warrantied out a bad sensor knowing that it was messed up because I changed out the original one brand new. I wander if those things spring out or something like that.

So no idling issues in park and everything runs just fine. Only other thing is my exhaust smell almost made me pass out. It's beyond rotten eggs and I doubt I have pumped gas with sulfur in it. More than likely, I need to change out the catalytic converter and the o2 sensor back there, but I don't always smell it.

The engine light went off for a very long time until I started my car after being at work for 8 hours then it immediately came on but I'm sure it's throwing codes for something else but I'll get it checked out later.

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Thursday, July 13th, 2017 AT 9:45 AM

CARADIODOC

MECHANIC
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Dandy. It sounds like you got a throttle position sensor for the wrong application. If you had to rotate it to get it to mount, it likely would have been reading something higher than the typical 0.5 volts at closed throttle. The Engine Computer would have to reconcile an idling engine speed with a TPS telling it the throttle was not fully closed. That confusion probably led to the erratic idle speed. Happy to hear you solved it.