This car has been driving us crazy. A couple weeks ago the car conked
out, we gave it a full tuneup (pcv plugs wires fuel filter air filter
serp. belt) and it got running again. It started off with 4 codes in
the computer, one of which was the MAP sensor (since replaced) now
we're down to this annoying P1374 code we can't seem to track down,
and we're at the point now where the car has a rough idle/skip and if
you give it some gas then let it return to idle, it'll die (you can
rev it for awhile no problem, as soon as you stop and it goes back to
idle, it just quits). We've replaced the crank sensor and the coolant
temperature sensor as well. The last 2 things we've been told to try
are the ignition control module and the harmonic balancer. If neither
of those 2 things solves it, we're at loss. Any ideas are
Does this skip/stall at idle affect performance driving at nomal
speed/loads? Is this a constant misfire, or just a rough idle stall,? If so
check the egr for not seating, remove and clean, try running the car with
the connector off. Does this stall happen from the first cold start or only
after it warms up. Have you cleaned the throttle body and iac for carbon
accumulation, check for vacuum leaks especially around the throttle body,
continually replacing parts is not the answer here, the base problem must be
found, it is possible you may have to consider getting this to a pro who is
familiar with these type problems.
maybe you should consider the conditions/actions prior to/during the
conk out.for clues.and fuel pressure.anybody put additives in tank
prior to conkout.can mess with injectors.how about injector
voltages/pulses.did you say it ran better with replacement ICM?where
did it come from?was the swap not available?(sure thing proof).you
coulda got another bad one?change the computer?popping cyl means
misstimed fire or lean mixture.like i said before.all kinky Gm problems
for me have either been ICM ECM or injectors for the symptems you
describe.but he first question i always ask anyone is if car has
recently been worked on or any special things been done out of the
ordinary.and then ask conditions during problem developement or event.i
remember a vw golf my daughter had that had a rough intermiitant idle
and stall problem and i finally after 6 months got a sub computer to
try and when i pulled the large connector i saw one of the wires had
come untrapped from the connector and so was making intermittant
contact .WHO KNEW!!and it was smothered in grease but i still caught
it!of course this was while removing test computer that failed to fix
I highly doubt a fuel additive would be throwing a P1374 code.
Slightly better with the new ICM however the symptoms have not
changed, the problem still exists. Came from autozone, brand new.
Highly unlikely, this wasn't a pickup from a junkyard this was a brand
That's the last thing we want to do. A *new* computer is $350 and
would need to be reprogrammed.
For the symptoms, AND a P1374 code, though??
Nope. Car had just passed inspection and had an oil change, actually.
After it started this problem and the check engine codes came on the
first time, we gave it a good tuneup (as per my original post) plus we
replaced the MAP sensor due to a P0108 code (IIRC). As I posted
already, this is either a wiring/terminal problem we are going to
attempt to trace down, or it's the computer. It doesn't appear to be
the ICM (as this did not solve the problem and the P1374 code is still
there) and it's definitely not something as over-simplified as just
someone adding fuel injector cleaner.
I got a hold of the GM troubleshooting rundown, which looks just like
the alldata steps, except in some steps it says something like "refer
to the Wiring Repair in Electrical Diagnosis book" so I was wondering
if you had such a thing. At this point it's looking like there's a
very complex electrical problem we need to attept to trace down, or
the computer is bad :(
Gotcha. If you have the factory manual set there is a book dedicated to
Electrical Diagnosis. The wiring repair you speak of is just a section
detailing repair procedures. Nothing specific to any circuit. I can turn the
ALLData version of the same thing in a PDF, but it's not going to help you
until you find the problem.
...or if there is a specific piece of information you need, I could send
You know, I just can't f'n win. Went to the library today, they have
all the mitchell manuals EXCEPT the one for 1996 in one section, and
in another section they have mitchell manuals that have these
wonderful wiring diagrams that would probably be great EXCEPT the
thing is in this big binder and none of the librarians know how to
undo it to make copies, because you can't take it out of the library!!
Use a digital camera and photograph the pages. Also a trip to
www.helminc.com might be in order. If you plan on keeping the vehicle and
fixing it yourself a good set of factory manuals is well worth the
how much does the boneyard want for a puter.and why did the wiring
problem suddenly develope?connectors?corrosion?chafing?insulation
failure?constant flex internal breakage?unbelievable fluke?(my VW)if
you were able to cure the other codes it does seem like a funny
deal.wonder why the new ICM only improved the running.can new parts be
faulty.it does happen occaisionally.maybe i'll go study that 1374
The answer to all your questions is: I don't know. The car was
running fine when my friend first got it, all of a sudden the check
engine light came on and it started running like crap. We have not
yet ruled out a wiring problem or a computer, yet. We got past step 4
in the alldata chart posted by Steve Mackie, now we are on step 5
(that means we did not skip to step 8 if you are following along).
Simply ran out of time tonight, will be working on step 5 in the
well if i'm understanding this 1374 thing(pdf)so far your car is
currently running on the 24x reference signal(crank sensor) and cam
signal.1374 means the ICM is ignored(3X) as an input to PCM.so then why
did the car run better with a new one?hmmmm.and even without ICM input
car should start and run on 24x and cam signal.you replaced the crank
sensor.you joked about the cam sensor.hmmmm.
After lots and lots of frustration, I believe we've found the problem,
it appears to be a bad wire. The circuit 430 wire, purple/white, has
no continuity. That's the 3x reference high signal for those
following along at home. And, obviously I got my hands on the wiring
diagrams (finally) or else we never would have figured this out.
Now of course, the question is, what type of wire is used, what gauge
of wire is used, and how in the hell are we gonna run the wire from
under the hood to the inside of the car? And after all that, is this
finally going to fix the problem...I certainly hope so.
Driving? What do you mean driving? We can't even drive this thing,
as soon as you take your foot off the gas, it dies :)
Constant, you can definitely hear the skip when you rev the engine.
Both. Have not checked EGR yet, thanks for the idea, will add to the
Yes, as part of the tuneup the intake was cleaned out with carb
cleaner. Have not found any vacuum leaks yet. This thing will be
either fixed or going to a pro soon before we rip the rest of our hair
Have you checked for a leaking intake manifold gasket? They fail all
the time on the 3.1/3.4 l GM engines and can cause all sorts of weird
problems. Also check carefully for any signs of water in the oil. The
first place it becomes visible is as a milky sludge on the underside of
the oil filler cap.
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