Was on a trip a couple years back in my 87 when I thought I'd blown the engine. turned out to be a blown timing gear. A word of warning, although you don't have to remove the engine, it's still a b*tch to change the gear.
First, there is a gear, not a chain, so more work to get it out; then alot of elbow grease to get the gear off the shaft. almost easier to change the whole assembly.
As for getting it out; remove r-rear tire and shroud. may have to drop axle to get in there, and it'll still be tight. A GOOD manual is a big help (Haynes or Chilton work but best if you have both).
Took me a while but was able to do it myself without dropping engine; a big plus in any book.
Good luck, hope it turns out well for you.
Another tip: any Fiero(87) you find in a wrecking yard, SCAVENGE PARTS, once they're gone, they're gone!
Still enjoy mine after 14 years, it's many quirks and problems notwithstanding.
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Brian Wolfe
shdwolf1@yahoo.com