CEl Code 124

[lwn]

94 Ex getting code 124, checked for vacuum leaks, 18lbs at idle. Replaced the pcv valve, checked air intake for leaks, cleaned throttle body, replaced tps. Sometimes the light will stay off for a week at a time, today came on and went off several times. Seems light will come on between when holding speed at 35-40 mph most of the time.

 

[MrShorty]

You didn't say, and my code list indicates that a 124 can only be a memory code, so I'm going to assume it is a memory code. Since this is the only code you list, can I assume it passed the KOEO test? Did you perform the KOER test?
124 refers to the throttle position sensor, which you've replaced. For now, we will assume that the replacement sensor is functional. Assuming there are no equivalent KOEO or KOER codes, it would appear that there is some intermittent electrical fault in the TPS wiring. 1st thing I would do is get my wiring diagram and my voltmeter and carefully inspect the TPS wiring to see if you can find a loose connection.

 

[lwn]

MrShorty, yes I have checked for KOER codes passed no problem, I have checked the wiring, checked the terminals on the tps. The tps I put on is new oem so I don't think that was the problem. I checked and tried a different Mass airflow sensor. At this point I don't know what to think.

 

[lwn]

Anybody else light is still coming on.

 

[MrShorty]

If the wiring appears to be intact, I would put a voltmeter across the computer at Vref while driving. Then when the CEL comes on see what the voltmeter is reading. Then backprobe the TPS signal wire and see what the TPS signal is doing when the CEL comes on.

 

[lwn]

Mr. Shorty, Thanks for the help, voltages check normal, what I have noticed is it is tied to the a/c defrost today stopped at a stoplight I hit the a/c button rpms went up to 1500 rpm at a stop never idled down, turned the switch off, idled down, got going down the road turned the a/c back on, let off accelerator and thing wanted to idle at 1500 rpm sped up then slowed down to about 35mph light came on.

 

[MrShorty]

This is getting interesting. Probably just missing something simple.
124 is the only code you're getting? If you clear the code (I prefer to pull the jumper wire during the KOEO test rather than disconnect the battery cable), does the 124 come back? If the 124 is the only code coming back, I don't quite see how the voltages could check normal when the light is on. You're checking the voltages when the light is on while driving? Checking the voltages in the garage or when the light is off is good for establishing "baseline" conditions, but the intermittant nature of this fault means we need to be watching the fault as it happens. The joys of diagnosing intermittent electrical faults .
It's interesting that the fault seems associated with operation of the compressor. It suggests that there is a crossed wire somewhere.

 

[Glacier991]

btw, IWN, Mr. Shorty is the very best on this board for tracking down these kinda things (always new good guys coming along so there may be others) so just understand his help here is priceless.

 

[lwn]

Well I hooked up a breakout box up and the light came on again, I just had taken it out and ran the heck out of it when I slowed to to about 35mph it came on the voltage was 1.24 volts, the voltage at idle is .92 volts. Also the engine was running at 1500 rpm's in park when I pulled into the garage. I changed the pcv valve, unplugged the hose going to the air intake hose, plugged the fitting erased the codes anr took it for a hard run down the same route I took earlier, the light stayed off and engine idled normal when I got home. The engine doesn't use any oil but could blowby be the problem?

 

[MrShorty]

Well I hooked up a breakout box up and the light came on again, I just had taken it out and ran the heck out of it when I slowed to to about 35mph it came on the voltage was 1.24 volts, the voltage at idle is .92 volts. Also the engine was running at 1500 rpm's in park when I pulled into the garage. I changed the pcv valve, unplugged the hose going to the air intake hose, plugged the fitting erased the codes anr took it for a hard run down the same route I took earlier, the light stayed off and engine idled normal when I got home. The engine doesn't use any oil but could blowby be the problem?

For clarification, is this what's happening?
1) Normal TPS voltage you measure when throttle is closed is .92 V, correct?
2) When CEL comes on and idle is high, TPS voltage at closed throttle is 1.24 V, correct?

Note that TPS voltage shouldn't be dependent on engine speed or any other factor (including blowby gases). Only throttle plate position should matter.

 

[lwn]

Tps measures .92 at idle, CEL came on at about 35mph foot was on the gas when I got the 1.24v idle was still .92v engine was idleing at 1500 rpm's.

 

[Eneurb]

I think a MAF problem could cause that code by not seeing the amount of air coming through that it should see at that throttle angle.

 

[MrShorty]

I think Eneurb is onto something there. I believe he is correct in that, an incorrect MAF reading could cause the computer to throw a TPS code. Basically the computer is seeing some inconsistency between the MAF data and the TPS data, doesn't know which one is at fault, so it blames one or the other (in your case, choosing to blame the TPS). However, in this case, it appears that the TPS is doing exactly what it should be doing.
I wouldn't jump out and buy an MAF. Lots of things can cause bad MAF data, not the least of which is air entering the engine from somewhere other than through the MAF. If I understood which hose you disconnected and plugged earlier, you removed the hose from the oil fill cap to the air intake tube (downstream of the MAF). I don't know about blow by gases, but if there were too much air coming through that hose (say from a leaking oil fill cap or a bad hose, maybe blow by gases if they are excessive), that would cause the MAF to read lower than actual. Some other vacuum leak could do the same thing. On EFI engines, vacuum leaks are a common cause of high idles, too.

 

[lwn]

I had an extra MAF, still doing the same thing, I did disconnect the vent hose from the oil fill and plugged it,, still no change. Took breakout box and checked all the sensor wires for shorts everthing checks fine. I have now changed the egr to an extra I had will see if it will make a difference. I have checked the air intake tube for any means of leaks and it seems ok. Can the vss or park neutral switch be a cause for high idle?
Vacuum at idle is 18lbs, I have clamped off every hose checking for a leak. Fuel pressure is 30 at idle, 40 with regulator unlugged.