Problem with '92 Corolla DX (funny noise)...Codes found

[87_SR5]

This problem just started today.

A funny noise is coming from under the hood. It sounds like a low DUD DUD DUD DUD...and it increases in speed with RPMs. I took a look and it didn't sound like it was coming from the engine...it sounded like it was with the air intake. So I removed the top part of the air intake box and the noise is coming from the intake hose that goes to the throttle body. It is a very strange noise. Also, with the parts I have removed, the noise is very loud, but then as soon as you give it any throttle at all, it disappears instantly.

However, even though it disappears when I have it apart (and give it throttle), you can still hear it inside the car when you give it throttle, just not as loud.

I have no idea what could be even making this noise.


I checked the ECU and pulled some codes. I came up with code 2 and 4 (or 24.....flashes twice, pause....then flashed 4 times....and repeats. I don't know how it is on the corolla.)

I do not have a manual at this time so I don't know what each code means. So if anyone can at least help me out with the codes, that would be very helpful.


Here is a sound clip that I took, just for fun....if anyone wants to listen. It is taken from under the hood with the top of the airbox removed, next to the air intake hose leading to the throttle body. If you listen, you can hear the noise stop when I give it throttle, but then start back up again once I let off. Here is the link: http://www.members.aol.com/jamy4us/t...ta/corolla.wav


Thanks for any help...

1992 Corolla DX 4cyl 69,000 miles

[TekPhobia]

That would be a code 24, Intake Air Temp sensor.

Here's a trick for ya...

Pop the hood, look at the motor. Look on the left side, near the firewall, on the intake manifold. See a blue connector? Good. With the motor running and the thud thudding away, unplug it. Now smile as the noise is now silent.

Congratulations! You've found your Idle Air Control Valve.

Now, there's a vacuum hose that connects to the fella that has the blue connector. Follow it down to a metal pipe(s) that's fastened to the intake runners. And oh look, it pops out the other side! (right side). See that bulb looking thing between the intake pipe and the throttle body? Reach your hand under and you should feel a hose. Is it connected?

Thank you for playing, "Name that sound."

>New Game<
>Start Over<
>Save Game<

-Tim

[87_SR5]

Originally Posted by TekPhobia

That would be a code 24, Intake Air Temp sensor.

Here's a trick for ya...

Pop the hood, look at the motor. Look on the left side, near the firewall, on the intake manifold. See a blue connector? Good. With the motor running and the thud thudding away, unplug it. Now smile as the noise is now silent.

Congratulations! You've found your Idle Air Control Valve.

Now, there's a vacuum hose that connects to the fella that has the blue connector. Follow it down to a metal pipe(s) that's fastened to the intake runners. And oh look, it pops out the other side! (right side). See that bulb looking thing between the intake pipe and the throttle body? Reach your hand under and you should feel a hose. Is it connected?

Thank you for playing, "Name that sound."

>New Game<
>Start Over<
>Save Game<

-Tim

Thanks for the reply...I will go try that right now...

-------------

Okay, I went out and did what you said. I found my Idle Air Control Valve and unplugged the blue connector. Once the engine was warm (it wasn't thudding as the engine was warming up...the noise wasn't there until the engine was warm), it wouldn't stay running when I unplugged the blue connector, but it did eliminate the noise for the split second I unplugged it.

I tracked all the hoses and everything looks fine. Could I have a bad Idle Air Control Valve?


I will mess around with it tomorrow, but I don't think any hoses would have come unplugged...it just started happening today. It ran great yesterday and this morning...it just started this afternoon.

Thanks for the help...

[TekPhobia]

Interesting. I'm wondering if either your idle is too low, ports in the throttle body are clogged or the IACV is bad. Does it idle real low?

-Tim

[ssrrww]

I tried the trick a few months ago. After unplugging the connector, and the sound disappeared. But at the moment I realized that how the idle is controlled, crudely, with the IACV.

I decided to plug it again. I don't believe this corolla has anything better to control its idle.

[87_SR5]

Originally Posted by TekPhobia

Interesting. I'm wondering if either your idle is too low, ports in the throttle body are clogged or the IACV is bad. Does it idle real low?

-Tim

It does seem to idle low, but I don't have a tach, so I don't know. From under the hood, as soon as you give it any throttle (just moving the linkage a fraction of a inch), the sound stops....and you can't hear it anymore (this is with the top of the airbox removed). But, inside the car when you are driving, you can hear it all the time, no matter what RPM.

What exactly does code 24 say?

Can you explain to me what the IACV's job is?


Thanks for the help...

[ratboycom]

code 24 is "Open or short in intake air temp sensor circut for .05 sec or more (THA)"- Diag
Trouble area: "Open or short in intake air temp circut, intake air temp sensor, ECU"

[87_SR5]

Originally Posted by ratboycom

code 24 is "Open or short in intake air temp sensor circut for .05 sec or more (THA)"- Diag
Trouble area: "Open or short in intake air temp circut, intake air temp sensor, ECU"

Thanks for the clarification on code 24.

Is there any testing I can do on the IACV to see if it is the problem or not? I do not have a manual for the car at the time, so I don't know. I will be picking up a manual from the library soon.

Can anyone tell me the job of the intake air temp circuit....or the job of the IACV?


Thanks

[TekPhobia]

Well, one of the tests is to disconnect the connector and see if the motor keeps goin. So it failed that test. You can remove it and clean the gunk out of it. Personally, I find it entertaining removing the entire intake manifold and cleaning everything on it...especially the EGR passage.

The reason the noise stops when you give it any kind of throttle is becuase....you're not in idle mode anymore!

The intake air temp sensor works in combination with the MAP sensor to determine air density. In other words, it's a variable in the formula. IIRC, the ECU defaults to 68°F if it's disconnected.

Check the airbox, near the brake booster. Should be a hole in the top part of the air box....that's where the sensor goes.

-Tim

[87_SR5]

Originally Posted by TekPhobia

Well, one of the tests is to disconnect the connector and see if the motor keeps goin. So it failed that test. You can remove it and clean the gunk out of it. Personally, I find it entertaining removing the entire intake manifold and cleaning everything on it...especially the EGR passage.

The reason the noise stops when you give it any kind of throttle is becuase....you're not in idle mode anymore!

The intake air temp sensor works in combination with the MAP sensor to determine air density. In other words, it's a variable in the formula. IIRC, the ECU defaults to 68°F if it's disconnected.

Check the airbox, near the brake booster. Should be a hole in the top part of the air box....that's where the sensor goes.

-Tim

So for sure the IACV is my problem since it won't idle with it disconnected????


So the air intake sensor is the one that is in the upper half of the airbox? Because I had this disconnected when I took the top of the airbox off.....but it was connected when I was performing the test you told me to do.

And the IACV works off the sensor (intake air temp sensor)?


Hopefully once I pick up the manual I will have a better understanding of the system.


Any other things I can do, besides checking to make sure all the hoses are connected? Anything I can do before I have to remove the valve and clean it?


So my problem is either the IACV, or the intake air temp sensor......anything else?


Thanks for the help...I appreciate it.

[ratboycom]

disconnect some of the vac lines (in a row one after another reconnecting the one before, before you check the next) and see if there is a strong vacuum on the line you dissconected (towards the manifold not the intake pipe)

[87_SR5]

Sorry for bringing up my old thread, but I thought I would do this instead of starting a new thread...


I am still having problems.

Today I went out and removed the Idle Speed Control (ISC) Valve. I disonnected the vacuum line coming from the ISC Valve and found out for sure the noise is coming from the ISC Valve. After some tinkering, it appears the the computer is rapidly opening and closing the ISC Valve, which makes the noise. When the vacuum line in connected, this noise of the valve opening is closing is transferred to the air intake box...making the low DUD DUD DUD I was describing.

And with the key on (engine not running), I can control the opening and closing of the ISC Valve by plugging/unplugging the connector.

So....I don't think my problem lies in the ISC Valve because it seems operational. Unless there is a resistance test I can perform on the Valve, I don't know what else I can do to see if it is bad or not.


If the ISC valve is not the problem, I have to figure out what would be causing the computer to open,close,open,close the ISC valve. From what I have read in the manual I picked up, there are several sensors that the computer reads to control the ISC valve.


If there is another test I can perform on the ISC Valve or if there is anything else I should check, please anyone let me know....



-'92 Corolla DLX 4A-FE engine... Code 24 (open or short in intake air temp. sensor circuit)....hmmm, could my Intake Air Temp sensor be bad?

Thanks for any help

[cobrajet25]

Originally Posted by 87_SR5

If the ISC valve is not the problem, I have to figure out what would be causing the computer to open,close,open,close the ISC valve. From what I have read in the manual I picked up, there are several sensors that the computer reads to control the ISC valve.

Uhhh...why don't you FIX THE DAMN CODE and see what happens before you tear your entire engine apart! The computer is TELLING YOU what the problems is, right? The computer is telling you there is a problem with the IAT sensor, and you can't figure out what sensor is causing the ISC valve to act up?! Did I miss something here?! Regards, Aaron

[87_SR5]

Originally Posted by cobrajet25

Uhhh...why don't you FIX THE DAMN CODE and see what happens before you tear your entire engine apart! The computer is TELLING YOU what the problems is, right? The computer is telling you there is a problem with the IAT sensor, and you can't figure out what sensor is causing the ISC valve to act up?! Did I miss something here?! Regards, Aaron

Its funny how you are the first person to say that in this thread....while before I was being told it was the ISC valve. You are right about everything....but I haven't done anything to the engine yet (oh, took the ISC valve off....a nut and a bolt)


Thanks for pointing out my stupidity... ME>>><<<YOU


Also, after looking at the diagnostic diagrams for the circuit, it says to check to see if the IAT sensor is bad by putting and Ohmmeter on it. I did this and came up with a resistance reading.....but the thing is the book didn't say anything about what kind of reading I should come up with.... should I be messing with this or just buy a new IAT sensor?

Thanks again

[fredk]