When my daughter's 95 Civic DX has been running a bit and she puts it into park, it eventually starts surging real bad. The car has 168,000 miles on it, just tuned up, new thermostat, new timing belt and water pump. Any ideas as to what may be causing this? This is not a minor surge.
Thanks!

 

The catalytic converter could have a little clog or something. Let the car run for a little while and then look underneath. If the cat is clogged, you'll see it glowing a little. If you don't already know what you're looking for, follow the exhaust piping back towards the front half of the car and you'll see a wide bulge in the piping.

If it's clogged, the engine performace will react depending on how much exhaust can flow past the clog. If it's restricted, exhaust will back up and choke the engine a little, causing the temp in the cat to drop as the flow of hot exhaust is decreased. When the clog cools and contracts, the engine exhaust will flow more as engine breathing is increased and cause a surge. But, then the clog will heat back up, expand, and choke the engine, etc.

 

Also, your PCV valve could have a clog. Get it checked out.