hey everybody,
i have searched numoruos times and i still can't find my answer.

so here is my q i recently had obx headers installed along with a custom cat.
i hooked up all the o2 sensors
and reset the ecu

problem while driving down the highway car runs fine. first time i stop or slow down the rpms drop down to zero and the car quits
try restarting car in busy intersection
no luck.

has any one ever had this happen?

So its completely dead right now? First you have to determine if its fuel or spark. Pull out a sparkplug, attach it to the wire and try cranking it and seeing if you have spark. Also do you have a CEL currently? Seems you've only modded the exhaust system and the only thing that would cause something like that is if the new cat collapsed and is choking the exhaust.

*quick edit* just had an epiphany... did you make sure you installed the cat so the exhaust flowed through it the proper way?

just replaced the plugs with bosch platinum
had an aftermarket intake, put stock intake back on
reset ecu still cel

the car runs fine, but if you take it on the highway and drive it at or above 50 mph then come to a red light it just stalls.
and it will keep stalling due to low idle.
check water pump, works fine
car is not over heating


not sure on the cat. how can you tell

With the cat flow thing it usually says it on the cat, at least the one I had bought did.... Get the CEL read and see what is it also.

cel reads
mass air flow sensor has too much air. but I have the stock intake.! reset ecu cleaned mass air flow sensor same thing. is the mass air flow sensor bad. this only happening at warm idle. when I had the exhaust installed I had to extend the 2nd o2 sensor wire by six inches to get it to fit after the cat. before I installed any mods. the car did idle very funny.

https://img.photobucket.com/albums/v...rientation.jpg

Check to make sure your MAF is facing the right way, and that your IAT sensor is installed like it is supposed to be.

yep that was the first thing I checked.

and I will also mention that the car runs fine if I am driving or accelerating. it only stalls when I stop and let off the gas or if the car is moving and I cruise to a stop. tightend up the slack in the throttle cable no diff.

THe IAT is your Intake Air Temperature sensor, it's the only other sensor IN your air intake stream other than the MAF. On the OEM intake, it's plugged into the filter box.

Can you post the actual CODE number of your CEL so we can look at Webtech?

I don't have the code only the description. as follows: MAS or VAS A circuit HIGH INPUT

what do you mean you dont have the # code?

how did you read the cel in the first place? the code is a 4-digit # that starts with a letter (for you, it'll start with a "P")


can you also make sure that you are not getting any misfiring cel codes... if you do, that'll be ignition or injector related

that would be MAF not MAS ...

Check if your MAF connections are ok, I know there was a recall about the MAF connection becoming loose because of engine vibrations ... don't know but it's pointing to the MAF, so it could be damaged or the connections could also be the problem!

I had vip scan the code on the way to work one morning. I was so mad I was late I didn't realize they never wrote it down. I believ it was either P1047 or P1017 not to sure though.


connections are fine. and there are no misfire codes. is there any way to test the maf and see if its faulty? and if it was bad would the car drive at all?

MAF circuit HIGH INPUT code is P0103 (I think ???)

As for the MAF inspection, I don't know ... try looking Webtech, I know there is a step by step MAF harness inspection but I don't know about the sensor itself!

that sounds like the code that they read off.

is it possible that when I extended the 2nd o2 sensor wire it could throw off the maf.

my car has 219,550 miles on it. so it is the original maf. I have cleaned it with maf cleaner no diff.


I have also noticed that after the car stalls. if I wait a couple minutes...about ten ... and then start the car it idles like crap. its not that the engine cools down but it has to be something cools. right

219,550 miles o_O. My 98 has 88000 miles..... Anyway, its most likely not the o2 sensor, but did you double check how it was extended? Maybe it was spliced incorectly or something easy to fix like that.

I've had MAF high input for a few reasons. Check out the thread I blew up my freakin' intake. You can't mess with anything inside the MAF housing, or it will mess up and give you that fault. Another thing to check is the physical connector on the side of the MAF, that will also give the same fault. Try cleaning hte MAF with MAF or Electronics Cleaner. Either one will work, they're the same thing, but MAF cleaner costs more. If all else fails, go to advanced and tell them you need a MAF for a 98 KIA Sportage 2.0L. It will save you about $100 if you need a new MAF.

well I checked all the connections everything fine. I decided just swap the maf with one from a 1998 elantra, exact same part everbody!!!!

as soon as I turned on the ignition. I could tell something was diff. the car idled at 1000 rpms and then dropped to an even 950.

now when I hit the gas the car doesn't bog down. . . it roars. I hate how one stupid piece can do that, but its fixed and the car drives great.

NOTE: when changing the maf. unplug the neg terminal off the batt. I did this and I had no cel.

ill have to explain how to install obx headers without getting a cel sometime... if someone hasn't already posted it.

thaks for all the help everybody

What kind of intake did you have on it? More particularly, what kind of filter? Oiled?

it was a metal mesh american racing something filter. stupid there stuff is worthless. all the sensors fit in fine but I don't believe it was the intake that did. the car was having trouble idling 6 months ago... and I didnlt take care of it in time.

on the side I will be buying a aem cold air intake in the future... can those ruin mafs?

^^ AEM has a dryflow filter which is amazing. It's high flow, probably the BEST flow, and there is no oil on it. You can even wash it with no problems. But a lot of people have problems with the oiled filters (K&N, Injen, etc) because the oil coats your MAF and throws CEL's. My buddy with a cobalt is fighting a never ending battle because of this. 950 is still a rather high idle though... Mine was at about 1000 when I got my car, and I've changed and cleaned everything and got it down to 750. You might want to check the gap on your plugs and maybe replace the wires. Fuel filter wouldn't be a bad idea at all at 200k+ miles.

yea, after all that abuse on the engine from trying to figure out what it was, treat it right and do a little inspction/replacement tune-up.

and do you like blue? I have a blue AEM cold air intake with dry flow filter. cool.gif PM's me

well I am sad to say that the maf is not the problem. the cat is choking off the exhaust after running full throttle. I believe the 2nd o2 sensor was wired bad. that is why the maf is going crazy.


is there any way to tell if the cat is plugged. would the car even run if it was plugged?

yes the car would run, a trick that was gave to me is to un-connect the exhaust before the cat, if the car runs fine, it's the cat ... though it's hard to do with the first cat! lolll

<div class='quotetop'>QUOTE (driftkid77 @ May 23 2007, 06:41 PM) <{POST_SNAPBACK}></div><div class='quotemain'>well I am sad to say that the maf is not the problem. the cat is choking off the exhaust after running full throttle. I believe the 2nd o2 sensor was wired bad. that is why the maf is going crazy.
is there any way to tell if the cat is plugged. would the car even run if it was plugged?</div>
Told ya it was the cat wink1.gif

If you pull the piping off you can easily tell if the Cat imploded.... My dad's santa fe did the same thing. The car runs for awhile until it chokes it self to death then it wont start for awhile until all the emissions is out of the system. Just replace the cat.

Easy steps for fixing the cat, unless you need to go through inspection. then your skrewed.

1. remove cat from car
2. set cat facing whatever direction you would like standing so you can see into it
3. Get a sledge hammer and a 2" metal pipe (preferably long enough to run though the cat)
4. beat the guts out of the cat untill you can see strait through it.
5. have a spacer welded into the exhaust to trick the secondary o2 sensor into believeing that everything is copesetic. (or get a wide band o2 sensor and know if there is a problem)
6. reinstall your newly created test pipe and enjoy much freeer flow through the exhaust.

objects needed.

misc wrenches (probably 15mm or 17mm for exhaust bolts)
3/8s drive wratchet
10lb sledge hammer
5' peice of 2" pipe

alright that sounds like a good idea, but I just realized that when I first had the headers put on. and no cat installed the car would stall at idle also.

I was only running off the 2d o2 sensor (had not extended the wire yet all stock) and I did have the short ram installed. could it be that there is soo much extra heat under the hood that it is causing something to go wacko?

and what else could it be if it isn't the maf or the fuel filter?

this is really frustrating!!!!!!

its something in your exhaust system because thats what you changed to cause this problem. The 2nd O2 sensor only reads if your Cat is working... The first O2 sensor reads the actual A/F mixture and has the ECU adjust it. Make sure that first one is working

alright sounds good. I have also noticed that the car will shudder really bad right before it quits... misfiring perhaps....no cel though.

and as for the first o2 sensor I unplugged it when I first had the headers installed and drove around for a week without it. the due to the car running really rich...I had the cat put in.

I put the first o2 sensor after the flex pipe. is that placed too far back? how does hyundai have the first o2 set up? does it also read temp?

Its just a simple 5v sensor I believe. Where you have it shouldnt be bad or at least it wouldn't cause this problem. Pull the cat off and take a look at it, thats the best thing to do right now if you haven't done it yet.

alright I rewirred the 2nd o2 sensor and used heat shrinks. one of the wire was touching the piping and kinda melted a litlle bit

also to off the flex pipe and looked into the cat.(i can't look through it because the shop welded it onto the "straight" pipe.

I can see that the cat is not pure whit .... but rather a light tan. is there any way to tell if its plugged just by looking at the cat? I don't want to punch a hole through it if it isn't the problem... you know .

Do me a favor, look at your TPS, what is the brand name on it? Keifco or Dae Sung?

just finished punching a hole through cat. test drove it and the car did the exact same thing...the only diff the exhaust was twice as loud.

this time I watched what happened to the tach..

1. let off the gas while traveling uphill and turning into my driveway

2. tach dropped sharply to 2500 rpms... from 3000 while in neutral

3. cel, brake, col, and batt light all flicked on then disappered....

4. then the tach drops to 0 rpms and all the lights come on for good

5. car quits

6 and I started to regret ruinig that cat.

what do you think the issue is

Answer my above question, and I'll tell you.

sorry about that its Keifco

Hmm, well, it's probably not your TPS then, even though the Keifco's can go bad too, the Dae Sung's have some serious problems.

Any vaccum leaks? Post up some engine bay pics.

I don't have access to a computer. I am using a pda.

however the car is misfiring especially at high rpms. and you have to drive the car until it is warmed up then it quits... it does not over heat. could it be the fuel pump?

the engine will bog down when i tap the gas really lightly and if i repeatedly do that very fast the car will almost quit.

Answer the following.

1. Mileage on the vehicle?

2. Last time you changed the fuel filter if ever?

3. Last time you changed the sparkplugs or wires?

You might wanna use a public computer, pics would help cut some of the guesswork out.

Also, does your PDA have a Camera?

1. Mileage on the vehicle?
219,950

2. Last time you changed the fuel filter if ever?
last summer

3. Last time you changed the sparkplugs or wires?
last week


yes it does have a camera




I have a funny feeling since I have tried everything else.

this all started when I changed the position of the 1st o2 sensor... it is now in the stock position of 2nd o2. . . has anyone ever heard of this killing the idle...????

<div class='quotetop'>QUOTE (driftkid77 @ May 24 2007, 04:36 PM) <{POST_SNAPBACK}></div><div class='quotemain'>I don't have access to a computer. I am using a pda.

however the car is misfiring especially at high rpms. and you have to drive the car until it is warmed up then it quits... it does not over heat. could it be the fuel pump?

the engine will bog down when i tap the gas really lightly and if i repeatedly do that very fast the car will almost quit.</div>

<div class='quotetop'>QUOTE (Jay-M @ May 22 2007, 02:24 PM) <{POST_SNAPBACK}></div><div class='quotemain'>what do you mean you dont have the # code?

how did you read the cel in the first place? the code is a 4-digit # that starts with a letter (for you, it'll start with a "P")
can you also make sure that you are not getting any misfiring cel codes... if you do, that'll be ignition or injector related</div>

i just had a feeling about misfiring... can you please explain if you are getting a cel at all for the misfires and what are they?

It sounds like spark plugs to me.