Code 24 and 31

[MassSupra89]

My car is throwing code 24 and 31. I went out for a few minutes and it started getting jumpy when I would let off the gas then press it again. I pulled into a parking lot and it started idling at about 400-500rpm. I come to a complete stop and it just stalls out.

The CEL comes on and it throws a code 31
I get home and check it again it throws 31 again.
I disconnected the battery for about 30 minutes and then start it up again.
Throws a code 31 and 51:icon_conf
I turned it off and started again and now it's throwing 24 and 31 continuesly.
I took my AFM off and it would idle VERY low, then reconnected it and it wont idle at all, just starts and shuts off.

I'm thinking faulty AFM?..Any helps appreciated guys. Thanks.

 

[MassSupra89]

Just started it up again and it idled fine for about 10 seconds, CEL went on and I tapped the gas and it just stalled out again.
Disconnected battery and tried again, stalled out.
Now it's only throwing code 31...

It did this 2 weeks ago when I went to the track but I disconnected the battery and the problem went away until now.

Anyone?

 

[MassSupra89]

Anyone?
I've searched but can't find the exact same problems I'm getting.
It's running extremely rich then just bogging and stalls, If i take it out of gear it wont idle just turns the car right off.
I just need a "Yea that happened and I did this now its fine" lol.

 

[jetjock]

Find it odd you're getting no reponse? Try a manual search.

Code 24 and 31 are both associated with the AFM. One is air temp and the other is airflow. Code 51 is normally associated with the TPS and is also associated with code 31. If I were you I'd test the AFM and check the TPS, for both intergity and adjustment. Read the manual to see how to do both things.

 

[Nick M]

If you step on the throttle when in diagnostic mode, 51 will set. Did you over oil a K&N, or do anything with the meter lately?

 

[MassSupra89]

Yea 24 is intake air temp and 31 is airflow, I haven't touched the AFM or intake in weeks, Don't have a K&N, I put a Magnaflow muffler on the other day(I was running straight catback with no muffler before) but I didn't see how that would throw my AFM,mixture,idle and everything off. I already pulled the muffler off and it doesn't affect it, still acts up.

I guess I'll test the AFM and TPS when I get home like you said Jetjock.
Thanks for the replies.

 

[jetjock]

Since the air temp sensor is a completey independent part of the AFM the code 24 could imply a wiring problem or a lack of +5 volt power to the AFM. Ohm the AFM but be sure to check the 5 volt supply pin on the connector. I find it hard to believe the air temp sensor and the Karman would die at the same time. That's what makes me suspect a supply problem or bad grounding. The code 31 is serious. An AFM fault will goof up lots of things as it's one of the two primary inputs the ECU depends on for engine control.

 

[MassSupra89]

Thats what I'm worried about. If the computer can't rely on the AFM I'm afraid it will create serious problems.
Needless to say I'm not driving it. But I'm worried about how bad the problem is. I just got home and checked the codes again and it's just giving me 31.
I'll ohm the AFM and give the whole thing a thorough lookdown in the morning.

 

[jetjock]

A bad AFM won't hurt the engine so the only "serious" problem you'll have is it'll run poorly. What happens when certain sensors fault is the ECU goes into fail safe mode. After all, what good would the car be if it stranded you every time a sensor went weird?

In the case of a bad air flow signal the ECU defaults to fixed values stored in memory and uses the starter signal (STA) and the TPS idle signal (IDL) to choose between them in order to set injection duration for starting and driving. It's set up this way to get you home if the air flow part of the AFM dies out on the road.

In the case of a faulty air temp signal it assumes a fixed value of 68 degrees but air temp doesn't carry anywhere near the same weight with the ECU as air flow does.

There are only two sensor faults that'll shut the engine down competely and the air temp or air flow signals aren't either of them. Bottom line? The car won't run well because air flow is one of two primary engine control inputs but the ECU will "wing" it. What it won't do is damage the engine.

Here's another interesting tidbit: fail safe mode isn't the same as back up mode. Fail Safe still uses the ECU's microprocessor. Back up mode allows the engine to run even if the microprocessor gets stupid or stops altogether. In fact every time you start your engine it's done through the back up chip.

 

[MassSupra89]

Just got home and Ohm'd the AFM, came up fine. no wires are disconnected or out of place as far as I can see, still throwing code 31 and wont stay on, starts and immediatly stalls.

 

[jetjock]

nope

 

[MassSupra89]

My meter has freq. I believe but my car won't idle...:icon_conf \
How would I go about checking it?
So if it's not internal to the AFM would it be my wiring, or the ECU not sending the 5+volt out.

 

[jetjock]

The ECU sends out 5 volts to everything so I doubt it's at fault. Has to be wiring or the AFM itself. Can you get the engine to run at higher than idle by holding the throttle plate open? Will it run with the AFM unplugged? It should.

Remove your EFI fuse for 30 seconds to clear all codes and start from scratch. With the key on or engine runnning measure between E1 (or body ground) and Vc for 5 volts. If you have 5 volts there then measure between E1 and Ks for AFM output using the frequency function on your meter. Look at your manual to indentify these terminals on the AFM. If you can't keep the engine running look for pulses out of Ks during cranking. There won't be many but they'll be there if the AFM is working.

If you get stuck you're down to either swapping in a known good AFM (just swapping the electronics is easier) or removing the AFM and bench testing it using a 5 volt supply and something like a muffin fan. If you don't have something that makes 5 volts you can simply blow air into the AFM while it's powered by the car and look for an output. Remove the air filter and put a small fan in front of the AFM.

Forget the rest of the car and think of the AFM as a separate gadget. All it does is convert air flow into a 5 volt pulse stream. All it needs is 5 volt power, ground, and air blowing through it to make pulses come out of the Ks terminal (referenced to E1 of course). If it does that the odds are excellent it's working. If it doesn't it's dead. If it's putting out pulses you need to confirm those pulses are getting to the ECU. It's as simple as that.

When you're done messing with all this check for codes again. While you have the diag block jumpered see if you get a code 51 when you slightly open the throttle and that it disappears when the throttle is released. Sit in the car and use the gas pedal. Be sure the A/C is off when you do this because if you turn it on it'll also give a code 51 even with the throttle closed. You can check to see if it does that too but check the throttle part first.