I have a 97 Tracker with 1.6L 16V that suddenly lost power. It has set no codes, I have had it on 3 different scanners nothing out of the ordinary.  I have checked the spark plugs run a compression test, it has no miss, when you first start it it won't go until it warms up some.  Cleaned the mass air flow sensor, new air filter, fuel filter, checked timing, checked for vacum leaks since fuel economy has gone from 25 mpg to 15mpg. Nothing has helped.
Has anyone had this happen to them?  Any other ideas on what to look for?  I know a lot of techs and used to be one myself for a long time, none of the ideas has panned out.
Any help would be appreciated.

EGR valve or O2Sensor.  

I had this happen, it was my fuel pressure regulator. Just fixed it this past week actually.

Cap, rotor, wires all in good shape?

Catalytic converter clogged?

Bad gas?

Throttle linkage OK?

Bad computer running in limp mode?  Did you pull the battery wire and let the computer reset?

Thanks guys. I was working on it again this after noon.
It has new cap, rotor, wires.  The O2 sensors seem to be pulsing correctly although I have not replaced them.
I thought about replacing the fuel pressure regulator although it does change engine rpm when unpluged so I don't think it's stuck.  There seems to be plenty of exhaust coming out of the tail pipe.  I thought about taking it to an exhaust shop to have them test the cat back pressure.  One thing I haven't done is ajust the valves but there's only 55,000 miles on it  I'm thinking about taking to one of the shops that has an engine analyzer and have it run through the paces.

55k would be a lot of miles on my '90's valves.

Have you checked the compression?

Well the power loss went running really bad and having to limp it home.  It turns out the mass air flow sensor went outI put another one in and it's running normal again.
One thing hang on to your bar stools if you ever have to buy one.  A reman from Beck Arnley is $500.00 + $60 core.
A new one from Chevy is over $900.00.
I think I found the only used one to be had in Albuquerque.
Thanks for the comments

Sounds like a nice spare part to
get at the wreckers before you need one

Where is the mass air flow sensor & what does it look like?  I agree, it sounds like something I'm gonna pick up next trip to the yard. I too have the 16 v 1.6 engine.

It sits just past the air cleaner box in the air tube.  It has a small square box on it with a 3 wire plug.  It's mounted to the air cleaner box with 2 bolts.

thanks