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  Dec. 27, 2011 3:30 p.m. miataman86 New Reader

  Dashpot wrote:

  BoxheadTim wrote:

  I only replaced the trans fluid in the turret and the shifter boots so I think it might be time for a rebuild of the shifter itself. I've got the two teflon washers on order with the local Mazda emporium, but they couldn't find the Mazdaspeed shifter bushing Woody recommended earlier in this thread so I guess I'll need another source for that.

  Don't sweat the metal bushing - it makes tougher to get into reverse and rumor has it they sometimes stick there once you're in. I've run it for several seasons (never stuck in reverse) and can say that it slightly sharpens an already very accurate shift throw.

  Another thing to check while you're in there - the "bushing bucket" bolt that attaches to the shift rod. Can't remember if the '95 has the same setup, but my '01 came with an awfully sloppy side to side throw. I bought and installed new bushings/boots only to find that bolt was loose when I popped the top. Original bushings were fine, bolt was 100% of the problem.

  Loc-tite could solve that problem

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  Jan. 9, 2012 10:13 a.m. BoxheadTim SuperDork

  Right, I iz back with more questions. Given the number of Miatas I have owned in the past I feel I'm really asking some dumb questions but anyway...

  There seems to be some very slight surging during acceleration up to about 3k rpm when the engine is lukewarm that never goes away completely but becomes barely noticeable. Poking around the Interwebs this is suggested to be either an issue with the coolant sensor at the back of the head or the O2 sensor, correct?

  More concerning is that there is a lot of judder through the drivetrain in fourth gear (and only fourth gear) at around 50-ish mph. It gets worse under load, too, so going up the pass to work has me shaken, not stirred. For some reason the judder isn't that bad in either 3rd or 5th gear, although I can't really put it in fifth gear uphill under load for any sensible amount of time. It feels like a tire that's out of balance, but I'm pretty sure it isn't.

  I had a quick look underneath, the PPF bolts are tight and the engine mounts look OK (but they also look like they're the originals so they might well be past it - the car has 125k on it). Any suggestions what to look at? Clutch is believed to be the original but I was thinking that if I'm putting too much torque through it and it's slipping, I should noticed that in both 3rd and 5th gear, too?

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  Jan. 13, 2012 12:58 p.m. BoxheadTim SuperDork

  OK, quick update. Cleaning the throttle body - admittedly not 100% thoroughly, and I didn't clean the idle control valve - seems to have reduced the 4th gear judder I mentioned above.

  However it's now developed a new fault - after I take the foot of the gas (say, at a light) the "idle" revs stick at about 1200-1400 for a good 10+ seconds before they drop down to the normal idle (around 750/800, and yes, I know I need to look into this). Any idea where to look for the "sticky" idle? Clean the TB again? Air leak?

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  Jan. 13, 2012 1:14 p.m. Keith SuperDork

  You cleaned off the sealant on your throttle butterfly, so now you have a leak your car is trying to deal with.

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  Jan. 13, 2012 1:18 p.m. BoxheadTim SuperDork

  Crap. It look like the cleaner didn't affect the sealant and it's still present, so I guess I just cleaned up enough to affect the way it seals?

  New TB/butterfly time or is there a way to fix it?

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  Jan. 13, 2012 1:18 p.m. mthomson22 Reader

  http://forum.miata.net/vb/showthread.php?t=446148&highlight=high+idle

  Probably what Keith said. But just in case you might check the above linkie.

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  Jan. 13, 2012 1:23 p.m. Keith SuperDork

  It's fairly common for us to get a call from people who cleaned up their "dirty" TB and now have a high idle. Sounds like you didn't get it all, usually the IAC isn't able to bring the idle down.

  I've seen it fixed with paint. Just close the throttle and shoot a little bit of rattlecan paint around the edge of the butterfly. Basically, paint it shut. Then crack it free when it's dry and voila.

  By the way, if you ever want to diagnose a potential problem with the IAC, just unplug it. Does it change?

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  Jan. 13, 2012 1:24 p.m. BoxheadTim SuperDork

  I'll check the stuff mentioned in the link - I know the TB isn't held open by the throttle cable (it does hit the idle stop) but if the 1.8L also have the air valve mentioned in the link, that might be part of the problem.

  The throttle body was extremely gunked up when I looked at it and most likely didn't seal right at that point, but there's a good chance that the spray-on cleaner might have dissolved the sealant, even though I used the proper throttle body/carb cleaner. Oh well.

  I'll unplug the IAC and see if that makes any difference to the way it idles, then will report back.

  BTW, apart from the paint fix, how much does a good used throttle body run at?

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  Jan. 13, 2012 4:23 p.m. Keith SuperDork

  FM Salvage has 'em for $30.

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  Jan. 22, 2012 5:26 p.m. BoxheadTim SuperDork

  I had another look at the throttle body and it very much looked like the throttle plate wasn't closing properly when I was trying the "hold a flashlight behind it" test. The coating on the plate still seems to be there, so my theory is that someone tried to tweaked the idle using the stop screw. When I de-gunked the TB I removed a 'ring' of deposits in the actual throttle body that probably had been enough to almost mask the fact the throttle plate wouldn't close far enough. Which explains why the engine revs would drop to about 1k rpm, stay there for a few seconds and then drop to ~850 before I cleaned the TB.

  Anyway, long story short - I tweaked the throttle stop screw slightly (probably 1/3 turn) and the idle now drops all the way to 850 straight away. Phew.

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