Wait a minute, have you had the issue checked out? It might be a sensor or something simple.
With car stuff, I tend to go by the price to repair (especially for a lower value vehicle). If the work is under $1000, I'll go ahead and do it. If it's between $1000 and $1500ish (maybe $2000 tops), then it's a bit of a lineball decision, based upon the general condition or market value of the car, and above that, it's time to dump it.
I spent $1500 on a new clutch a bit over a year ago. In hindsight the money would have been better spent on another car, but I've got another year's motoring from it so I guess it's not too bad. My thinking at the time was that selling it with a busted clutch, I'd barely get scrap value, but as a going concern I'd at least get a bit of money if I decided to sell. Of course now the water pump is leaking and the suspension is worn, and I'm ready for another car, so this time it's getting replaced.
Would you consider DIY with parts from the junkyard?
After 15 years and 180,000 miles it's on borrowed time. If it's a cheap fix to keep it going, by all means do it, but if another $2K job is required on it, time to get rid of it.
Ultimately it depends on your own situation. If you're in a critical job, a long commute or have young kids the threshold for keep/replace might be lower than for someone who doesn't need the car as much.