Wow, I hope you're wrong! PM'd with a few questions. Thanks so much for the help.

Try installing BRK5 NGK spark plugs gapped at .020" and see if that does it. If it does, you have a weak coil pack.

I could be right... The change off timing will cause a great difference in exhaust temps. causing the cat to go deffect...

If the engine throws a cell from the emptied cat (what should happen) you can try to take the last lambda sonde out off the exhaust and plug the hole.
As the 1st sensor sees bad air and the 2nd ambient air this could work.(normally it measures the diff created by the cat)
(as long as it trows no cell don't bother this)

Cam timing could be off too. My exhaust cam was a tooth off when I bought the car cause it "has a new timing belt". After a few days I pulled it down and put another new TB, and found the old one was installed wrong. The exhaust cam was a tooth off, and fixing it made a difference in power on top end.

Yep, this also is a good one..

Rotate the engine until timing mark (down) is spot on.
http://www.miata.net/garage/images/TBELT5.JPG

Check the marks (highlighted in white below here) There must be 19 teeth of the timing beld between them.
http://www.miata.net/garage/images/TBELT6.JPG

I pulled the valve cover today. The cams are 19 teeth of timing apart, thanks for the tip. I put a timing light on it and it looked like it was jumping back and forth between 10 and 11 degrees before tdc. I've been running premium in it, if that makes a difference (I read that '99s didn't have adjustable timing and they adjust timing based on a knock sensor... I think that's right anyway). I didn't want to dig any deeper into it today as I need to get to work tomorrow.

I gotta make this some kinda contest or something... Whoever correctly identifies the problem will get a bright shiny new Flyin' Miata 1.6 -> 1.8 throttle body adapter, shipped directly to their door!!! Ohhhh! Ahhhh!

Did you move the crank to see the timing mark on the gear???Or did you only see the top gears?? (gear is located behind the plastic covers...You only need to remove the top cover and shine a light inside to see the gear.)

If you saw the bottem gear on time,top gear on time, timing should be spot on... Meaning both (above) pics will be on time. But this doesn't mean the keyhole is ok ....
Pull out 1 sparkplug (key out, handbrake on, gear in neutral.)

Find out what the top point off the engine (cyl 1) is (You can use a socket extention in the sparkplug hole. Youll need the highest point.
The gear must be spot on TDC http://www.miata.net/garage/images/TBELT5.JPG

If this is ok, timing is not the issue.

Do not look at the pulley & timing adjustment mark on the plastic cover.. It is useless for this...


Next thing is spark plugs/ wires and fuel filter.

QUOTE: it looked like it was jumping back and forth between 10 and 11 degrees before tdc.

You must connect TEN and GND to see a stable and correct timing mark...
Only the 99+ have no scematics anymore in the diagnostic connector.
See this page:http://www.miata.net/garage/ignition.html#timing


QUOTE: they adjust timing based on a knock sensor...

No they reduce timing only when knock occurs. On hot days, heavy engine loads, low rpm/full trottle this can happen.
It's a savety device.

[/QUOTE]

99's have two marks on the balancer. Align them with 0 and 10* on the plastic cover and that puts the motor at TDC on #1. Couldn't hurt to verify that it's right with an extension in the spark plug hole, but either way there's no reason to pull any TB covers.

I said it's the plugs. Change them to NGK's and set to .020.

I only looked at the top gears. I didn't know how far I had to go pulling stuff off to see the lower gear and didn't want to pull apart my daily driver on a work night. Plugs, wires, and fuel filter have already been replaced so they aren't the problem. I think I'm going to hold off on the lower pulley until next weekend. I don't want to end up trying to replace the timing belt when I have to work the next morning.

Did you use NGK spark plugs? What gap did you set them to? What brand wires did you use? Just cause you replaced them with something doesn't mean it's not that. These motors are pickey about some things. My motor doesn't run right on Champion plugs. Dunno why, but it likes NGKs.

Plugs have been changed from NGK's to new Iridium NGK's. I gapped them closer to .040, as everyone else seemed to suggest. You're suggestion to gap them to .020 seemed to be in order to diagnose weak coils, which have already been replaced so that is not the issue. Are you suggesting that the plugs are simply gapped to wide? Or did you miss that the coils have already been replaced?

Plugs are NGK Iridium gapped to .040. Wires are Magnecor 8.5mm competition wires.

Put regular plugs in it and gap them to .020 and I bet your problem goes away. Try it. It's cheap. I suggest running regular plugs all the time anyways. It doesn't call for Iridiums. Don't use em. Less gap won't hurt anything and if you have a miss at higher RPMs, then less gap will fix it. I know you said you "swapped" coils. Doesn't mean you fixed anything. 99's are known to have weak coils. Swapping around weak coils is just moving a problem around, not fixing it.

Off topic...
Good to know.. i have a 95 block with a 99 head... And only 1 timing mark at 10 degrees... None at 0... I did not know for 99+ models.

Alright, I'll be back in 20 min and let ya know what happened. :wavey:

Switched back to the old plugs, gapped to .020 and took it for a spin. I thought it helped a little bit at first but I think it was just me being optimistic. Still feels like the car falls flat on it's face in higher RPMs, barely accelerating at all. I guess it could still be the coils, I'll PM the guy I bought the coils from and see if I can get a little history on them.

Thanks again to everyone helping. I love you guys.

You know, if the main cat was plugged, the pre cat may be plugged too. It's built into the manifold. Have you punched it out yet? If the main one died surely the pre cat is done.

Wow, I didn't know there was one... I thought that was only on the Cali cars?

I think all 99's had the pre cat. Mine did and it's not a cali car. It's called "the boat anchor". That huge cast iron manifold has a pre cat built into it. Double check, but I'm 99% sure all NB's have a pre cat.