What would cause my 97 eclipse 2.0 dohc to run at 3500rpm.
Sounds like the ISC is stuck wide open or you have a big vacuum leak. Check for those first especially if it just started doing this, if you can't find anything then a system scan is needed.
Search Maintenance & Repair Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Maintenance & Repair Experts