Hate to be the bearer of bad news, but... get a block check (note that mine passed their initial check. It wasn't until they pressurized the bad cylinder that they saw bubbles in the radiator.)

A used motor with a (claimed) 86K-mile prior life and things are good. I don't know if it was the block or the head and don't much care. To me it's obvious that the misfires on Cylinder 3 I have been experiencing for several months were a small crack leaking coolant into the system that would eventually blow out and it would recover and run fine until next time.

It just decided to get worse one day to the point of noticeable coolant loss and, eventually, constant misfires. Never saw anything at the tailpipe that I would peg as indicative of a leak. Weird.

Hopefully this motor gets me to 250-300K (and beyond) on the odo.

 

@ Bang- I have experienced the exact same symptoms as you and I think I have also noticed coolant loss. What is going to be your course of action? A bottle of junk to try and seal the leak? Pop the head replace head gasket and have the head leak checked?

@ diu head- did you figure out what the root of your issue was?

 

I had a used motor installed.

 

Check the radiator for exhaust gas. Find some? Start pulling the head and get it checked. Could be just head gasket. But dont just keep driving it.

 

Do i have to get some sort of chemical coolant checker to check for exhaust gas in the radiator, or is there a poormans way? I will google this really quick. I was thinking of turning each cylinder down to bottom dead center or slightly on the way up so the valves are closed and hook up my air compressor to the sparkplug port using a compression tester lead and look for bubbles in the radiator.

 

It cant be the 02 sensor or any other sensor, unless this rough idle occurs after operating temp. Is reached because of open loop mode. When the ecm goes to closed loop 02 sensors adjust air fuel ratio but until then the ecm has a written map for open loop.