Idle dip......Gearbox problems?

[Hot Rodders]

I have a 99 build 2000 1st reg NB with 23000k on the clock. Recently, at times when coming to a stop at lights etc. the idle will dip by a couple of hundred revs and then return to normal idle. When I first got the car, there was talk of a gear box problem with late NA & early NB with a thrust bearing? problem. Can anyone advise where I can find details ( have looked but can't find ) on this matter. Do I need to worry?
Hope some one can help.
Cheers!

[Li7hium]

What is it like on starting up?

Have you recently had a dead battery?

Sounds like a problem I had after my battery went dead a month or so ago. In my situation, I had to alter the manual idle speed. ECU kicks in a tad afterwards which accounts for the idle speed coming back up, but if your base idle speed is below 800 RPM then you are going to keep getting the dip until the ECU kicks in.

Matt

[Hot Rodders]

Starts normal. No battery problems. Very intermittent at this stage.

[Li7hium]

Fair enough, if you do want to check your base idle, see this thread which has a link to the Miata Garage page dealing with idle issues.

Good luck in the search for the remedy.

Matt

[Hot Rodders]

Thanks Matt, but it is the Thrust Bearing? problem that sits in the back of my WARNING system in my head. I know it was on this forum, but could now be archived.

[Li7hium]

I've done a few searches on the archived forums. Are you getting a screeching sound at idle, or grindy grindy noises?

All of the threads I've looked at regarding thrust bearing issues either have a rattle of the clutch when depressed or a scratchy / screechy sound.

[Matty]

A thrust bearing would have failed in the first few feeks of ownership.

I'd be guessing contamination of the throttle body - either clean it, or adjust the bypass screw.

[EGG80X]

I got the same problem on my NB, seem like its a common prob with NB8A stated on the Miata.net

try different spark plugs and leads?
or
try different weigh engine oil?

[Alf]

I had this problem on Pumpkin, my old NB8A. A set of leads fixed her right up.

Cheers,
Alf

[Garry]

If the thrust bearing in the engine is stuffed the revs will slow when you push the clutch pedal in. It has only happened to a relatively few cars in the US. I've never heard of it happening in Australia so I think it sounds like it's a problem for US engines. I wouldn't stesss to much about it if I was you.

Sounds more like the base idle speed is to slow to me. I'd try adjusting that first as it's the easiest/cheapest thing. This is a tuning issue and totally seperate to the thrust bearing thing. Idle dip has been an MX5 problem in varying levels of severity from the first NA's to the last NB's. Especially once they get a bit of wear on them. It wont affect engine longativity. It may eventually drive you insane though if you cant find a cure.

The only thing that helps my idle dip is cleaning out the idle bypass screw passage. It's a right PITA to get the idle adjuster screw out but after a good spray of throtlle body cleaner down the screw hole and a general clean of the throttle body it idles like it's supposed to.

Just be careful not to strip off the black sealant stuff around the throttle plate with your throttle body cleaning or it'll be idling to fast............dont ask me how I know this.........

[Hot Rodders]

Thanks for your imput guys. I don't feel so stressed now that it seems that the motor most likely won't spit the dummy on me. At least I can let it go till the weekend.
Much appreciated.
Cheers!
P.S. Would a trip with the club to the dyna tune day be of any advantage? No mods have been done.

[Blugg]

I've got the same problem too. It goes away when the car is warmed up though. Only on cold start.

[Insurgence]

I've go the same problem.

I think it may be because fo the ignition leads. (i get 3 cylinders sometimes but it fixes itself up)

[Woo]

Having learned to live with the idle dip over the last 18 months I found that when I replaced the fuel regulator today that I no longer dip

Might just be the blue cars way of saying thanks for more fuel, but none the less worthy of a mention.

Wòó

[fig]

I've got the same problem too. It goes away when the car is warmed up though. Only on cold start.

ditto