Surging engine
 

2001 Elantra, 130K miles. In neutral or park, engine surges between 1500 and 2500 rpm, up and down. Replaced the IAC and today the injector "O" rings. Before I replaced the "O" rings today I could get the surging to settle down by spraying carb cleaner around one of the injectors. Thought I had found an air leak so I changed the rings. Surging is still there but now spraying carb cleaner has no effect. Any ideas?

Check the throttle body and leaks between the MAF and the throttle body. Also could be a leak between the upper and lower intake manifold. That gasket may need changing.

^check what novaresource suggested. Also make sure your throttle cables have slack in them. Did you replace the IAC gasket? Also make sure that the throttle plate set screw hasn't been tampered with. The set screw should have a plastic plug covering it to keep people from tampering with it. If all checks out surely sounds like an air leak. Try clamping off your brake booster vacuum line to see if idle settles down. If it does either booster is leaking vacuum or the master cylinder oring between master cyl. And booster is missing..

Before I read the replies I took the car to a local repair shop. Apparently on the way there the surging stopped. It was replaced by a 3500 rpm idle! Mechanic thought it was the TPS. He said resistance always read "0". Put in a new TPS and nothing changed. I checked the resistance on the old and new TPS's and they matched. Bought an Idle Air Controller even though the installed one was only 2 months old. No change. Both had the same resistance measurements. Returned both parts. I unplugged the IAC connector and the engine settled down to a 1200 rpm idle. Took it for a 5 mile test drive (with the IAC disconnected). Ran well. When I pulled into the garage and put it in park the idle shot up to 3500 rpm again! I than got on the internet and read your replies. I will check the things suggested next. Thanks, Friz