Miata problems (idle)

i have a 1994 miata. On cold starts, or after the car has sat for a few hours, it starts fine, and idles fine, but after say...30 or so seconds, idle drops to 4 or 5 hundred RPM and it sounds like its barely staying alive. If you leave it it will pull itself together after another 30 seconds or so and everything after that is fine. Also, sometimes, it seems when im idling or putzing around a parking lot or if it dogs a bit beofre i shut it down, it diesels a bit. Like the key is off, but it will cough once or twice like its still tryin to run....

Whats the deal?

As always, thanks

Take a peek into the throttle body and make sure it's not all gummed up with varnish.

I'd start by checking the base idle setting. Get the engine up to temp. Stick a paper clip between TEN and GND in the diagnostic connector underhood, then adjust the idle screw to get your idle to 850.

Don't clean out the throttle body. Idle problems in a Miata usually come from a gummed up ISC, bolted to the bottom of the throttle in this case. If you clean out the throttle, you'll usually wreck the seal between the butterfly and the bore, leading to a high idle.

I have had the same problem with my 97. It has at least temporarily healed itself. I have found that if when it happens, I turn on the A/C, the bump in idle from that will make it more driveable until it decides to behave on it's own again.

i may have written it unclearly... it will idle fine once warm, but on cold start it does the weird idle thing

Idle Air Controller? I hope it isn't this. They're like $800.00 from Advance Auto. A bit less from the stealer.

That isn't a typo.

They can usually be cleaned.

Keith wrote: I'd start by checking the base idle setting. Get the engine up to temp. Stick a paper clip between TEN and GND in the diagnostic connector underhood, then adjust the idle screw to get your idle to 850.

How do you ensure 850 RPM? Can a tach/dwell meter be used on a Miata? Or do I need to buy another expensive tool?

And on a sorta related note, is there an inexpensive program/cable that can hook up my laptop to an OBDII connector and find this?

You can get close enough to 850 using the tachometer in the instrument cluster. 500 is too low, 1000 is too high