Rough idle on Passat 1.8T 2003 engine code AWM
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  1. #1
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    Rough idle on Passat 1.8T 2003 engine code AWM

    I need help clarify two thihngs that came up while troubleshooting a 2003 Passat 1.8T (153K miles): Rough, stuttering during idle, misfire, etc. - not resolved.
    I have searched this forum, Googled on this issue and I am somewhat confused on two things - does this car have an ICU or not? If it does where is it? Several posts, including the one in the Information-Base section on B5 point to similar issue and recommendation that ICU may be the problem.
    However I am getting conflicting information on this. The engine code on this car is AWM and there appears to be no ICU on top of the air filter box. I also saw another post at justanswer.com where the mechanic actually stated that this car does not have an ICU?!?
    wher is the ignition control module on a 2003 passat - JustAnswer

    The second item I need help clarify is the term ICU itself as there are couple other terms used and I am not sure if this is the same thing or not. Which one is it that is being referred to when it comes to ignition: Ignition Control Module (ICM), Ignition Control Unit (ICU) or Power Output Stage?

    There are several threads on this topic with images that would definitely help but looks like images are missing because http://www.clubb5.com is dead - which is a shame.
    Based on some comments and write ups this article would be a good resource on the topic but is unfortunately also dead: http://clubb5.zeroforum.com/zerothre...=331320#331320
    This article in the Information Base and provides good info but is for engine code AEB I think (images dead also): Ignition Control Module (ICM) Install Procedure

    If you can help clarify this for me and/or point to the right link, it would be much appreciated.

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  3. #2
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    This is what the passanger side engine compartment on this car looks like. My understanding is that on some engines the ICU should be right here on top of the air filter box. This one (AWM) looks like doesn't have it
    vw_passat-passanger_side_engine_air_filter_box_1_small.JPG

  4. #3
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    Lucky for you, there is no ICM on the AWM motor! The ECM sends a direct signal to the coils of each cylinder when to fire. In later models (after engine code AEB, the original 1.8t motor in the B5 lineup) the ICM (pretty much a high powered amplifier) was built into the coils themselves. Remove the engine cover and you'll have four of these:


    Check first to make sure they are seated properly by pushing down on all of them (simplest fix, but rarely the problem.) If you know which cylinder is misfiring than swap two of the coils with each other and see if the misfire moves with the coil itself. Coils are easy to deal with, unplug, pull up with your hands (or special tool if you have it) to pop it out, and than go from there. Install is easy, press them in until they pop into place, and replug. If misfire moves with cylinder, replace that coil, no problem because they cost $20-30. If the misfire persists you might be looking at a brittle wire that separated in the harness, but try the other two diagnosis procedures and report back before we get into all of that. It goes cylinder 1 by the front of the motor (closest to the belts) cylinder 4 in the back (closest to firewall.)

    Good luck!

  5. #4
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    Ever serviced your PCV valve & lines? I had a complete split in a breather hose that caused rough idle and a misfire, I'm at 143k on my '04 1.8T AWM.

    Info: CEL, codes P0303 and P1136 - diagnosis?

    If coils check out you may want to investigate PCV.

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    Thank you very much for clarifying the ICU situation.
    @vbora01: Yeah, I already went through the coil packs one by one. I bought a whole set but ended up only using one to just test. replaced #1 one, tested, replaced #2, tested, etc. No change on replacing any of the coil packs. Meanwhile I also checked the spark plugs and although they could use replacing there was no immediate damage or corrosion present. I would be very interested in hearing more on the
    brittle wire that separated in the harness
    you mention.

    @doyles-1.8T: I did not look at the PCV valve and lines. I will definitely take a look and post my findings.

    Do you guys think I should also look at replacing the fuel filter?

    The details on the issue I am experiencing are as follows:
    Stuttering during idle when engine warms up. If I let it idle long enough it'll eventually start misfiring and the SES/CEL starts blinking. No apparent power loss or roughness or jerkiness while driving. It seems to be related to the ambient temperature where the stuttering becomes apparent as it get's warmer outside. This is just my observation and I am not sure if it is related or just my imagination...
    I've had the code for "Random misfire" come up twice over winter, but it went away (the SES/CEL cleared). I am assuming because the condition no longer existed after the determined number of qualified trips. Now the code has returned and in addition there are others:
    * Bank 1 system too lean
    * Cylinder 1 misfire
    * Cylinder 2 misfire
    * Cylinder 4 misfire
    * Random misfire

  7. #6
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    You can replace the fuel filter, but it does not usually cause this issue.

    Listen for any hissing under the hood at idle. While idling and it is stumbling, try this. There are two hoses coming off of the intake manifold right next to the throttle body. One is an L shaped hose that leads around the back, the other snakes down under. Clamp off the one that leads under. See if idle improves. If it improves, you have a bad PCV bleeder valve. It's a one way valve that is a known failure point on these.

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    Now that I look at the hoses there is a very minor crack on the valve that's right on top. In the hose that is coming out of the top of the intake manifold. The crack is only visible if I move the hose a bit but definitely a crack. Could that be the issue?
    @VAGguy: I will try your suggestion probably tomorrow evening and post my findings.
    Edit: the valve the is cracked does not appear on the diagram so I'm guessing this is not it...

  9. #8
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    hatman, after a botched attempt at removing PCV hoses mine idled rough enough for blinking CEL - then return solid once driving again. Highly doubt a check valve is the culprit if idling that rough (although you obv need to replace that too).

    Note my PCV bleeder valve itself didn't look too bad and there was not as much gunk in the lines as I anticipated. Breather hose coming up from oil filter area had cracked all the way through and severed. It's plastic and right next to the engine.

    I had to lay on top of the engine and peek through intake manifold to see it.

  10. #9
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    @doyles-1.8T: can you tell me on the diagram below which hose (#) was the one that was of plastic and cracked on yours? I felt and looked as best as I could through the hoses under the intake manifold but i did not see any thaat was plastic or cracked. I'm probably missing something.

    I have actually already replaced one of the hoses and the valve on what I believe to be the breather hose. The old valve was cracked in half. It's part #24 on the diagram (VW part # 06B103217R) which I bought from the dealership for $50. I also replaced most of the vacuum tubes at that time.

    @VAGguy: when I removed the hose you mentioned, there was definitely a change but not for the better - it was hissing and popping and sputtering with that hose removed. I actually remember that once I realized the valve had cracked I just replaced it with a plastic tube and it ran without the valve just fine until I got the part from the dealer and replaced. I'm adding pictures later.

    My next best bet will be to replace the check valve that is cracked. i may just try that with another plastic T first to see if there is any difference. Next is fuel filter.
    Any other ideas on what to check?

    Here is the diagram (it looks like the same diagram that doyles-1.8T had posted on another thread here):

    passat_1-8T_hoses.jpg
    Last edited by hatman; 03-19-2012 at 03:39 PM. Reason: added the link to the diagram on the post by doyles-1.8T

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    Here is the cracked valve:
    IMG_1714_Small.JPG

  12. #11
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    And here is the breather hose valve I had replace about a year and a half ago. I pulled the valve and made sure it was not cracked and that the membrane in it was working. All was good with that valve. But there is another two handfuls of similar looking valves all over the place... The one I replaced is dead center of the picture. The original was black but the replacement one is gray.

    IMG_1717_Small.jpg

  13. #12
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    Quote Originally Posted by hatman View Post
    @VAGguy: when I removed the hose you mentioned, there was definitely a change but not for the better - it was hissing and popping and sputtering with that hose removed. I actually remember that once I realized the valve had cracked I just replaced it with a plastic tube and it ran without the valve just fine until I got the part from the dealer and replaced. I'm adding pictures later.
    I never said remove. If you remove, the intake manifold will just suck in air, doing exactly as you described. clamping it means pinching the line shut.

    Sounds like you are talking about that larger valve assembly at the back that the L hose is connected to? That's the suction jet pump.

  14. #13
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    Looks like I somehow misread your post
    The valve I replaced about a year and a half ago is the one on the below image circled in red. I also removed it yesterday and tested it.
    IMG_1717_Small_annot.jpg

    Edit: BTW - I did not see any issues with that valve. That *is* the breather hose valve - correct? It's #24 on the diagram.
    Last edited by hatman; 03-19-2012 at 07:07 AM.

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    hatman, my breather hose that cracked in half is #2 on your diagram (both diagrams). See where it thins as it enters #5 (rubber t-housing)? That is where it split, just before the clamp.

    What you circled is simply a check valve. PCV bleeder valve is #6A in the diagram. Reason there is a split: Earlier models used 6 b/c they don't have that third nozzle going up to #24. 6A is later models with line #24 added to mitigate sludge.

    I replaced 2, 5, 6A and 10 - that whole line, and obv the clamps as well (7, 8, 11, 12 & 27 are just clamps). Also replaced the suction jet pump which is not pictured there, will bumpdate my thread with p/n's and what not...hopefully tonight, don't have info w/ me @ work.

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    Ok, I can see that now... But I gotta ask - how the heck did you get in there without removing the entire intake? Does the end of pipe #2 that goes into the crank case come out by just pulling on it? What are the rings #3 and #4? I'm assuming these are dealer parts - correct?

  17. #16
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    I'll include how in bumpdate. #3 is just an o-ring that fits inside #2, #4 is a retaining clip...very similar to the CTS clip (coolant temp sensor).

    No, not dealer parts - I reused the clip, bought new o-ring with rest of my parts online.

  18. #17
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    Just read through the "Interesting Link about removing un-needed vac lines and check valves" (original link here) here. Boy do I want to do that... I may give it a go one weekend when I'm emotionally ready

    I subscribed to your thread you're going to bumpdate so I'll read through that as soon as you post. Thanks so much doyles-1.8T.

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    OK, so definitely the hose #2 is split right as you said where it thins and enters into the rubber T. So you're saying that sucker is causing all that mayhem huh...

    For now I just plugged the lower L shaped hose as VAGguy said with makeshift plugs and clamped. I think that hose is #10 on the diagram. Runs nice for now.

    Here is what it looks like. That is as close as I can get to it, had to remove several other hoses just so I can touch it. There's some oil all over the area.

    photo(1).jpg

  20. #19
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    Go nuts, compiled everything I could think of into one post: CEL, codes P0303 and P1136 - diagnosis?

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    Update to the above is that I got the plastic breather hose (#2) and connecting components finally replaced (almost a year later), but there was no change
    I had plugged the lower L shaped hose coming into the intake as VAGguy had advised and that provided temporary relief. While doing the whole timing belt, water pump, belt tensioner replacement I also went for the breather hose. It had cracked on the backside which I did not even see, all the way through. While working on that I also cracked the oil dipstic... which I later replaced. So if you're going to work on this breather hose, please be mindful that the oil dipstick is probably very brittle from the heat, being near the engine and you need to be more careful than I was. I ended up removing the alternator to gain better access to the breather hose. I have pictures of the work and can post them if anyone is interested but I believe there are a couple of good timing belt writeups here already so may not be necessary.
    However after all that, when plugging the L shaped those back into the intake, the studdering and misfire came right back. So no change there. Next thing to check is the bleeder valve (#6A on the diagram in post #8) while I'm back in there again next time.
    The latest is that it now has low oil pressure... I will be going for the oil pickup screen and sludge cleanup and will do oil pump replacement and the rod bearings at the same time as well, since I'm there already, to see if that resolves the low oil pressure issue.
    Last edited by hatman; 03-23-2013 at 12:11 PM.

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    Just checking, as I just went through pretty much this whole adventure you're having with my GF's AWM... L-hose cracked....changed it. New PCV valve (up top) Coils fine. New plugs. After all that, finally asked her what kind of gas she last put in the car....She had been using 87 Octane regular grade since she got it (despite my warning when she got the car)....Threw in a bottle of octane booster, and the car ran like a champ instantly..

    You didn't use 87 did you?

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