Are there any other symptoms other than the sound and possible lower mpg's? I just (as mentioned in other threads) installed a "0" mile 2.7 engine and a new clutch in my Gen3. I believe I have an exhaust leak of some sort but was wondering if it would cause my 4Runner to surge when I let out the clutch slowly in first gear or in reverse, almost like a sudden loss of power then a jump? All the trucks/cars I have owned have been stick. I have put about 800 miles since the rebuild and I cant seem to break in this clutch. Do you guys think I possibly got a bumb clutch? Thanks for the help. It is now at the shop but some imput from you guys would help in case they try to pull a fast one on me. Thanks-George

Any imput? Please help a newbie.

It's possible an exhaust leak could let in enough air at low RPMs to confuse the O2 sensor. It would think the mixture was lean and add more fuel, hurting your mileage. You wouldn't notice anything at full throttle but at part throttle you might notice some surging.

Thanks 98OzarksRunner, you hit the nail on the head! When the engine was installed the gasket between the exhaust mainfold and the muffler piping was crushed. The air being allowed in was causing the O2 sensor to send a faulty signal resulting in the surging in lower RPM's.