99 sonata 2.4l stalling problem

A neighbor down the street came over with a 99 sonata 2.4 that he
bought and it stalls quite badly. He has put new plugs in it and it
had a timing belt 10k ago at 125k. No codes are pending but could have
been erased when he put in a new battery last month. I can not get my
autoxray scanner to pull a map sensor reading. If i disconnect the map
sensor it does NOT throw a code. all of the other sensors do. The map
sensor seems within specs when i use a volt/ohm meter as far as my
alldata shows. It's a little old like 2003 version. Shouldn't the map
sensor give me a code even after driving it 3 or 4 different times with
it unplugged ??? or is maybe the ecm going bad ???
thanks for any and all replies.

carl

 

After thinking about this it's a stumble or hesitation on the low end.
more than a stallaing problem. sorry was using my neighbor's words
instead of mine.

carl

 

I'm surprised unplugging the MAP sensor didn't trigger a code, but that's
not important. The MAP sensor isn't the problem. It's sole function on
this vehicle is to detect EGR operation.

There's a remote possibility that the stumble is an issue that will be
solved by an ECM reprogramming. According to TSB 03-36-019, the reprogram
will address "infrequent minor engine hesitation after an initial cold
start (typically the first start in the morning)." The words that make me
think this may not solve your neighbor's problem are "infrequent" and
"minor."

I doubt there's any issue that would require ECM replacement. This is
very, very rare on Hyundai. If I had to guess, I'd suspect a faulty air
flow sensor or an air leak between the air flow sensor and throttle body.

 

thanks hyundaitech ,
I will do the test on the air flow and even borrow one to test on it
monday or tuesday. The only problem with the ecu is that there is no
code by unplugging it on a 2 and even 3 trip detection. There is a
definate difference with it plugged in and not plugged in until it gets
to normal operating temp. I used to replace lots of caps in the old
mitshibishi ecu's that caused erattic problems and thought this might
be the case of these but since it's so hard to get out I would check
with you before I tell my neighbor that it is going to involve a lot.
I did pop the cover and check the timing marks and all is in alignment
just because he had a belt put in a while back. When it's cold (40 or
so) it stumbles worse but after a lengthy warmup it's noticable but not
to bad. Another thing i noticed was that if you did a restart after 5
minutes or so it would stumble for about only 15 to 20 seconds or so
and then would be pretty good but cold is another matter.
Thanks again and if you think of anything else please let us know.

Carl

 

The things you post seem to point at the reprogramming. You might ask the
dealer to do that for you. It may even be covered by your 8/80 emissions
warranty on the ECM.