Rough idle, Im fed up!!!
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  1. #1
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    Rough idle, Im fed up!!!

    Hello everyone, I'm experiencing a rough idle at a standstil while i have my foot on the break and my gear in D on my 99 passat 1.8t. And i went through all the previously posted threads on here to find out what people with the similar problem did to get rid of this problem. Well from what i read the possible solutions were:

    1Vac leaks
    2Dirty Throtle Body
    3faulty MAF sensor
    4motor or engine mounts

    Well i removed my throtle body and gave it a good cleaning, then i checked for vac leaks, then i had my motor mounts replaced, and finally replaced my MAF sensor and the rough idle has not gone away. At this point im just FED UP and thinking about just forgetting about it. However if anyone finds out a solution to my problem please let me know.

    Thanks to all! I love this web site ive saved so much money with all of your help.

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  3. #2
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    This might help

    Try this thread : Problem with RPMS lower than idle...

    Don't know if your car has a tip tranny or if that even matters. Worth a look though.

  4. #3
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    Very interesting, I bought mine used with what I thought was a rough idle but have no way of knowing for sure. Putting it in neutral raises the revs by about 100 and smooths it out completely. What is the idle supposed to be set at anyway? Mines at around 600-700. And it's a Tip. Where is this switch located?

  5. #4
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    Ouch vac leaks get you every time. Well it got me at least!

  6. #5
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    Quote Originally Posted by Five_fiver View Post
    Try this thread : Problem with RPMS lower than idle...

    Don't know if your car has a tip tranny or if that even matters. Worth a look though.
    yeah i have a tip tranny and it is definitely worth a try. Thanks for that ill try it and let yall know if anything happens.

  7. #6
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    here is the path in which you should take, in terms of troubleshooting and maintaining the above mentioned "four possible causes"

    1) Clean the maf.
    i just wrote a walk through that leads you through the surprisingly easy, and not as scary as one would have thought proper method to clean it. here.

    2) check your vac lines. although this can be at the same priority as the above maf cleaning, the maf should be cleaned, regardless. do the maf first, just to get it out of the way. it'l make a bit of a performance difference. as for the pertinence of the vac lines being replaced/checked, it would likely be better at the vehicle's age to just say "to hell with it" and replace the vacuum lines anyhow. it costs less than $5 to do. really easy job. just be sure to cut the hose off the nipples, or you will end up buying a new N75 valve.

    3) throttle body cleaning. this could clear or a bit of a problem, i would kind of put this on the same level as the maf cleaning, as it's pertains to the air injection system. cleaning it would be a very good idea regardless. i'm doing mine tomorrow, with a spat of seafoam, should i find time.

    4) engine mount swon't really cause that big of a deal... mine were bad for the first ~10,000 i had my car, and i never noticed. between then and now, i can see a bit of difference, but it doesn't make that big of a bother to me.

    now, here's where we come into play with other alternatives.
    5) how are your spark plugs? they should be changed at around every 40,000 miles.

    6) how are your spark wires? do they pose any problem?pluck them off and check for rust inside on the area where they grab the spark plugs. any at all rust can cause problems.

    7) how are your coils? are they performing on their appropriate output?

  8. #7
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    This seems to be a common issue with these cars; one without a simple fix. I had the same shudder/vibration in gear at idle, and tried most of the common fixes. Oddly, they all worked. New plugs helped slightly; cleaning the throttle body more so. The most recent work, changing the transmission fluid, helped most of all. (To me it always felt like the engine was straining against a drag or resistance at idle).

    Note I do NOT recommend everyone with lot of mile on their ATF jump to do a change; search the forums for dangers. My fluid had been in there over 200,000 miles.

    Now I want to know why I only get a slight vibration when stopped on a downgrade. Yes, the motor, transmission, and snub mounts are fine.

  9. #8
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    I used to have problems with rough idle and also the revs would suddenly increase by themselves whilst driving! the problem: Engine Coolant Temperature Sensor! I refitted after getting the fault codes read by vag-com and it all works fine! I would get the car checked and if so, replace the sensor. It's easy to do - 20min job however I lost all my coolant!

    See if you have any of these symptoms....

    http://wiki.ross-tech.com/index.php/01039

    Hope this helps

  10. #9
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    Quote Originally Posted by scotts13 View Post
    This seems to be a common issue with these cars; one without a simple fix. I had the same shudder/vibration in gear at idle, and tried most of the common fixes. Oddly, they all worked. New plugs helped slightly; cleaning the throttle body more so. The most recent work, changing the transmission fluid, helped most of all. (To me it always felt like the engine was straining against a drag or resistance at idle).

    Note I do NOT recommend everyone with lot of mile on their ATF jump to do a change; search the forums for dangers. My fluid had been in there over 200,000 miles.

    Now I want to know why I only get a slight vibration when stopped on a downgrade. Yes, the motor, transmission, and snub mounts are fine.
    it has to do with the application of the forward clutches in the transmission, and that it's held.

    what happens is that the entire output shaft is held solid, by the brakes holding the rotors holding the hub holding the axle holding the output shaft holding the input shaft, holding the torque converter's turbine.

    as we all know, or should know, the engine's power is NOT directly connected to the transmission's powertrain. the only physical connection the engine has to the transmission is the front fluid pump, which is turned by the casting of the torque converter, which is bolted to the flywheel which is bolted to the crank.

    what's happening, is the holding of the turbine while it's being pummeled by the hydraulic spray from the torque converter's "front pump" it just creates that vibration.

    the only way to fix this is to do a transmission rebuild with a new valve body, clutches, and torque converter.

    if you don't like it, then drop the car to neutral while you're coming to a stop, that's the ONLY way to stop this feeling.

    sorry this may not have been the answer you were looking for, but this is precisely the situation you were referring to in that last post. the vibration with the car in drive, at a stop.

  11. #10
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    Thanks, sipes. The inside of an automatic transmission is one of the few things I've never explored on a car, so I can't fully visualize your analysis - but it makes sense and is consistent with what I and others have experienced.

    At this point, my vibration is small enough that I wouldn't think it unusual, except that it had previously been so bad. And I suppose at 207,000 miles, the transmission doesn't owe me anything.

    While we're here, a question, since you seem to be an expert: The remaining oddity my tranny has is a very occasional slam! when entering reverse. This only happens when the car is warm and has been driven in forward; then put in reverse and backed up a hill. (My in-laws have a steep downward driveway) The transmission shop says this sounds like a "split reverse band" but says if that's the issue it should happen all the time. Odd.

    I guess the upshot is, it'll have to be rebuilt at some point.
    Last edited by scotts13; 02-18-2008 at 11:45 AM.

  12. #11
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    Thanks to everyone for their help. I will get to replacing my vac lines later on this week and i will report back soon. I cant say it ebough but I LOVE this site!!!!

  13. #12
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    Quote Originally Posted by scotts13 View Post
    Thanks, sipes. The inside of an automatic transmission is one of the few things I've never explored on a car, so I can't fully visualize your analysis - but it makes sense and is consistent with what I and others have experienced.
    While we're here, a question, since you seem to be an expert: The remaining oddity my tranny has is a very occasional slam! when entering reverse. This only happens when the car is warm and has been driven in forward; then put in reverse and backed up a hill. (My in-laws have a steep downward driveway) The transmission shop says this sounds like a "split reverse band" but says if that's the issue it should happen all the time. Odd.
    you're welcome for all the info. i just took an automatic transmission class, as i'm in mechanic training. it's really cool stuff.

    and that SLAM you feel going into gear can also be interpreted as "rocking"
    this is what farmers do when their trucks are stuck in mud, they slam it between D and R as the transmission will slam, and hopefully get them unstuck.
    as far as what your mechanic says? he's full of crap. there is no broken reverse band. if it was broken, or split, you wouldn't have ANY reverse, let along a loud slam when going into gear... it would cause a lot of other problems as well, due to the way the reverse band is put to gether and mounted.
    if it was split, it's mountings would come loose and the reverse servo would grind on the shell of the input shaft assembly. what actually is bad, is that you've possibly broken the damper/actuator spring. i forgot the actual name of that little damper/actuator piston, but it acts as sort of an expansion tank. the valvebody will rush the fluid into the hole to compress the clutches as fast as it can, and the spring acts on this "piston" and as the fluid is being shot into the spot at it's speed, the spring helps to act as a buffer and reduce the pressure of the application.
    think of it like this... the spring can only hold so much psi of pressure on that piston. as the pressure quickly builds up, the spring slowly is smushed under the piston.
    eventually, the spring overcomes the pressure, and a little bit of fluid is released by a check ball at the bottom of this piston's travel, and it returns.

    i'm looking at the ZF transmission manual for our cars as we speak. i bought it because it sounded cool, and has helped me a lot already.

  14. #13
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    Thanks again. Still means the transmission will have to be rebuilt eventually, but nice to know what's going on (and what isn't). Since that slam! only seems to happen once or twice a year, I'm not too worried, for the time being.

  15. #14
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    Quote Originally Posted by scotts13 View Post
    Thanks again. Still means the transmission will have to be rebuilt eventually, but nice to know what's going on (and what isn't). Since that slam! only seems to happen once or twice a year, I'm not too worried, for the time being.
    actually no. these pistons are reachable, by removal of the valvebody in MOST transmissions. unfortunately, i can't go too deep into this as my "repair manual" is strictly the teardown, and reassembly guide.
    gives no help as to that part. though usually, it's just remove the valvebody, be careful of which screws go where, as it's likely a 2 piece valvebody, and it should be back up in there. though i really don't recomend doing this job, because right behind the valve body is basically a large sheet of metal, in the shape of the valve body. this is called the "pressure plate"
    though, it's what lies behind this that's bad. lotsa little check balls. if you drop one and you don't know where it goes, you are completely SOL.

    though if you manage to do ok with that, then it's a matter of having an air compressor and blower attachment, and just pop it out by forcing air onto one of the channels that meets with it.

  16. #15
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    Just curious if you have found the reason for your rough idle because I have been having the same problem lately, too. My issue is that when coming to a stop at a light, the idle will dip from 800 rpms down to 600 or so and back again a few times and the car will shudder each time. This happens for about 10 seconds. Then it usually smooths out somewhat.

    However, I tried a can of BG 44K Fuel Injector Cleaner and the problem seems to have almost disappeared. I don't think this is the ultimate solution, but it helped. Here is a link to it for you if you're interested:
    http://www.autobahnpower.com/products.asp?recnumber=542
    Last edited by Five_fiver; 02-26-2008 at 10:03 PM.

  17. #16
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    Quote Originally Posted by userbigc972 View Post
    Hello everyone, I'm experiencing a rough idle at a standstil while i have my foot on the break and my gear in D on my 99 passat 1.8t...
    Quote Originally Posted by Five_fiver View Post
    ...Don't know if your car has a tip tranny...
    Not trying to bust your chops too hard, Five_fiver.

    I've done the same thing myself.

  18. #17
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    Quote Originally Posted by Stymie View Post
    Not trying to bust your chops too hard, Five_fiver.

    I've done the same thing myself.
    ...and let me guess - someone else corrected you then like your correcting me now? You feel better? That's what I get for not thinking too hard before posting hehe

  19. #18
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    Quote Originally Posted by Five_fiver View Post
    When we hook up, the first round's on me. :biglaugh:

  20. #19
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    Quote Originally Posted by Stymie View Post
    When we hook up, the first round's on me. :biglaugh:
    Ok, just not Moosehead

  21. #20
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    When you get this rough idle, do you get it every time coming to a stop sign/light or just from time to time? I have a V6 tip, that does a very similar thing, but it seems I have to be in a stop and go traffic for it to happen. Just coming to a stop in D on my daily commuting seems to be fine.
    So the consensus is that this is transmition related?

  22. #21
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    Quote Originally Posted by tomaszp View Post
    When you get this rough idle, do you get it every time coming to a stop sign/light or just from time to time? I have a V6 tip, that does a very similar thing, but it seems I have to be in a stop and go traffic for it to happen. Just coming to a stop in D on my daily commuting seems to be fine.
    So the consensus is that this is transmition related?
    I was getting it almost every time I came to a full stop. As I said above, a bottle of fuel injector cleaner almost eliminated it. Sounds like you need to go through the steps like others have suggested on here to narrow it down. Good luck!

  23. #22
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    Quote Originally Posted by Five_fiver View Post
    I was getting it almost every time I came to a full stop. As I said above, a bottle of fuel injector cleaner almost eliminated it. Sounds like you need to go through the steps like others have suggested on here to narrow it down. Good luck!
    I went through cleaning injectors already many times.

  24. #23
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    Check post #6 above by sipes. Good info. there.

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