code 31 only at idle? randomly

[stevenr816]

i just swapped a gte in my 89 and i randomly get code 31. the car only does it from 1000rpm and lower. when its under 1000k it acts like there is no maf, but when its above 1000k it runs great and pulls strong. it acts better when its warmed up. when i drive around from ~1400rpm and lower (auto) the CEL randomly comes on its never constant.

I have changed the MAF with 3 different ones, also the ecu, and tps. car has around -17-18 of vacuum. I have rewired the maf connector also.

any thoughts? the only thing that hasnt been changed is the cps. when i first put it in it had a code 12 for rpm signal below 1000rpm.

so maybe a cps or the cold start inject since it acts better when its warm?


Summary: code 31 randomly, never constant. changed maf 3 times, tps, ecu, and rewired the plug. no change. maybe cps or coldstart?

 

[rayall01]

Just an FYI! It's an AFM, not a maf. I'm just telling you this, so you don't get reamed a new asshole for calling it the wrong thing. I see that you rewired the AFM connector. The intermittent nature of your problem seems to indicate that the plug is loose, or the contacts are dirty. I've seen a lot of posts about loose AFM plugs. I would try cleaning the contacts with a small brass wire brush, and then find something to hold the plug tightly in place, maybe some zip ties or something. Beyond that, it's a mystery to me.

 

[kotu100]

its deff. your plug. i have this same problem right now. i think it has something to do with that lil gasket inside the afm plug.

 

[stevenr816]

the plug is 100% clean

but like i said its only at idle in low rpm and acts like there is no maf, other then that it drives perfectly and pulls hard


also afm=maf same freakin thing, just like maftPro tuner???

 

[kotu100]

the plug is 100% clean

but like i said its only at idle in low rpm and acts like there is no maf, other then that it drives perfectly and pulls hard


also afm=maf same freakin thing, just like maftPro tuner???

haha afm and maf is not the same thing. go tell that to one of the old-timers.

and like i said, its your afm plug, or afm itself. i was having this same problem. only wiggling the plug can fix it. i still havent found a way to fix it 100%

 

[jetjock]

Indeed they're not the same thing although both are used on L Type (air flow metered) EFI systems.

What do you mean by under 1000K (that's a hell of an idle btw) it acts as if there's no AFM? If everything is working right you could unplug the AFM and drive around all day as long as you took it easy and didn't go over 3000 rpm. And rather than guessing why not simply measure Ks?

 

[stevenr816]

Indeed they're not the same thing although both are used on L Type (air flow metered) EFI systems.

What do you mean by under 1000K (that's a hell of an idle btw) it acts as if there's no AFM? If everything is working right you could unplug the AFM and drive around all day as long as you took it easy and didn't go over 3000 rpm. And rather than guessing why not simply measure Ks?

thats what happens when replying on your phone lol. it only has a code 31 from basically 0-1000 rpm. its never constant i could pull up to 5 lights and it idles fine, or i could pull up to the next 10 and it has code 31 and pulses in idle. keep in mind its an auto.

i checked codes today and had
24 intake temp
31 afm
34 overboost (57trim)
51 and ac/tps

so im sure its something with wiring seeing how its both sensors in the afm ad ive ran 3 different ones with no dfference. however i did change out the tps today to see if the code 51 would go away and it did, started great, ran great then i adjusted it alittle and it then ran like crap. when i start it i usually have to give it alittle gas to get above a certain rpm.

im changing the plug tomorrow to see what happens. whats the possibility of maybe a valve not fully seating causing lower then normal vacuum? i watched it today in the light so i could see and at idle i had anywhere from 17-13 negative. it does have a louder then normal valve tick maybe cylinder 1/2

 

[hvyman]

2 clues. code 24 and 31. both are for the afm. a loose connection will give this intermittent problem.

 

[stevenr816]

im changing that today, the plug. but i replaced the tps last night and all the codes went away except 51. and everything went away mostly. so i think the tps connector is bad since now it happens even less

 

[IwantMKIII]

^51 means your TPS is not correctly set in the right position.

 

[kotu100]

or if you didnt reset the codes after messing with the tps it might still be stored.

 

[jetjock]

51 doesn't get stored...

 

[kotu100]

ahh ok, now i know

 

[jetjock]

Good. That you learned something new today makes us both happy

It's a real time code used as a diagnostic aid that never gets set in memory. If it did it'd get set every time the gas pedal was stepped on. Only code of it's type in the system.

 

[kotu100]

OP did you change the plug? any change in the symptoms?

 

[stevenr816]

havent changed it yet but tomorrow i a changing the tps and afm plug. simce changing the tps helped abit. arent the tps and afm interlinked through out the wiring?

also today on a decent drive on the freeway i noticed that just while cruising it will handomly miss or loose power for a split second then get back on. i know the tps is adjusted wrong cause if i give it gas it wont do anything then bam theres power.


how is the code 51 used for a diagnostic aid? i dont have a stop screw so i cant adjust the tps like it says to in the book, any suggestions?

 

[stevenr816]

so i know somethings loose if chaninging those connectors dont work i will try a new harness =(

 

[stevenr816]

also im going through gas like crazy full tank 16.5 gallons, ive driven 130 and have 1/4 tank left

i changed the tps plug, no change, changing afm plug now

 

[kotu100]

also im going through gas like crazy full tank 16.5 gallons, ive driven 130 and have 1/4 tank left

i changed the tps plug, no change, changing afm plug now

yea its deff your afm then, if its unplugged or working incorrectly you'll go thru gas like nothing.

 

[stevenr816]

yea its deff your afm then, if its unplugged or working incorrectly you'll go thru gas like nothing.

ok to make things worse i have hard wired the afm and tps straight to the ecu with a new plug and the same thing!

and i have tried 3 different afms, that work perfect on other cars