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I'm working on a 98 Mazda 626 GF 2L with an automatic transmission. While I'm used to driving manuals, I would say that the amount of vibration when sitting stopped in drive with the brake on seems excessive. The excess vibration goes away when put in neutral. I also noticed that when first taking off or in certain types of acceleration it feels mushy, like there is a lack of power until suddenly I get a solid feeling. All this is in addition to a rough but stable idle when in park.

The tranny fluid is pretty old and dark ( it hasn't been changed for five years and about 80,000 kilometers ), however it's not dirty - there is no grime or particles in the fluid and there is no burnt smell ( I asked more than one person to smell it ). Also, the gears engage immediately without hesitation when I shift it into drive or reverse.

Due to this I don't think it's the clutches. While I have little exp. with automatics, my gut feeling is that the torque converter maybe isn't working as efficiently as it should and isn't locking as soon as it should. I think when it finally feels solid and powerful that is the torque converter locking.

If I'm correct about the nature of the problem, could changing the old fluid out and adding something like lucas transmission fix improve the situation? Or do those types of products only help with worn clutches?

If that won't help, how big of a job is it to change a torque converter and is it an expensive part?

EDIT

Another thing to consider, could this just be a symptom of problems with the engine idle? When in park and I press hard on the gas the engine seems to wobble / shake and if I go to WOT it's very noticeable and I'll even hear a belt slip for a moment.

EDIT 5/1/2016

OK, so after putting in a new Lambda, valve cover gasket and plugs, things are much better, however I still feel like there is excess vibration and I think there might be more than one cause.

The problem is worst when I first start the car, and gets progressively better as everything warms up. When everything is cold, and I switch into D, the vibrations are very pronounced. Once both the engine and tranny are warmed up the vibes are much less noticeable. The thing is that once warm and I switch into drive there is a momentary drop in rpm from about 700 to 500, during which there's allot of vibrations, then once the rpm recovers the vibes kind of smooths out, but don't go away completely.

Some thing that might be relevant:

  • there is no noise accompanying these vibrations
  • the vibrations go away the moment the car starts moving
  • I can downshift while driving and hit the gas and it responds immediately
  • generally the tranny seems to be performing pretty well
  • I noticed that the engine itself seems to be vibrating more than I would expect at idle
  • one of the engine mounts looks pretty beat up ( I'll put up a pic later )
  • the ATF is dark and heavily oxidized, but still clean

Sooooo, I'm thinking maybe changing the ATF and fixing the motor mount might solve the problem.

EDIT 6/1/2016

Here's that pic of the engine mount. I figure being able to stick my finger through it is a problem:

enter image description here

This is what a new one is supposed to look like:

enter image description here

EDIT 6/1/2016

So I changed the ATF and that doesn't seem to have made a difference.

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  • My suspects here would be bad engine mounts, bad transmission mounts, faulty idle air control system, misfiring cylinders. Your observations about lack of power and vibration across the rev range makes me lean towards the possibility that one of the cylinders is misfiring
    – Zaid
    Sep 21, 2015 at 16:06
  • @Zaid I did a power balance test and didn't notice significant differences when pullling each plug wire. However that might be a false negative since I've got the idle air screw completely open to keep the idle at 750. I did that because it was going below minimum idle and lugging occasionally. When ever I let off the gas I always get a soft landing of the rpm's about 250 above base idle, before it drops to base idle after a second or two. Does that indicate a properly functioning IAC?
    – Robert S. Barnes
    Sep 21, 2015 at 18:08
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    Don't use the Lucas as I don't believe your transmission/TC is at issue. This is the same car you've been working on for a while. I still think something is going on with a vacuum leak or unmetered air or something on the fuel injection side and not the transmission. Too bad you didn't have a wide band on the exhaust or could tap into the OBDII to see what things are doing. Another thing you can do is pull a temp on each of the cylinders at the exhaust manifold to see how equal they are. A cold exhaust port is rich and a hot one is lean. May indicate something to you.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Sep 21, 2015 at 22:19
  • Regarding your spark plugs update - those plugs don't look too bad. The car may run slightly smoother with new plugs but they are not the root cause of the vibrations at idle.
    – Zaid
    Sep 25, 2015 at 10:57
  • @Zaid I don't think they're the root problem either, but I interpret the relative condition of the first plug on the left as indicating the problem is in that cylinder, maybe the plug wire or the injector.
    – Robert S. Barnes
    Sep 25, 2015 at 11:21

1 Answer 1

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I would check the motor mounts sounds like your may have a cracked one but it could also be that you have a vacuum check valve attached to your Power Brake Booster that has gotten old and needs replacement, or there may be a vacuum leak elswhere check your vacuum hoses.

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  • Looks like you nailed it with "check the motor mounts"! (There may be other issues, after all it's a '98).
    – kmarsh
    Jan 7, 2016 at 17:19
  • I have a completely worn out passenger side motor mount, I'm going to change it soon and we'll see how that works out.
    – Robert S. Barnes
    Jan 20, 2016 at 10:49
  • Changed two worn out mounts and no difference.
    – Robert S. Barnes
    Sep 27, 2016 at 6:17
  • Changed two more worn out mounts ( driver side tranny mount and tranny bridge mount ) and that didn't help at all either. Only one left is the rear engine mount which looks fine.
    – Robert S. Barnes
    Aug 21, 2017 at 13:31

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