I have a 2002 Reg Cab 2.4/5sp 2wd 104,000 miles. I recently purchased it at 100K. It is stock. I essentially freshened up all the systems. Complete Fr and Rr brake job including fluid, flushed coolant, new shocks and front springs, wheel bearings, 4 new tires, alignment, new fuel filter, air filter, plugs (gapped correctly) pcv valve, tranny and diff fluid, Amsoil 5w30 oil and filter change, cleaned the MAF and sea-foamed the motor. It is does not burn or leak oil, does not appear to have any head gasket or vacuum leaks, tech went over entire motor with stethoscope. No plumes of white or blue smoke or coolant in the oil. I did have trouble with the exhaust. There were leaks throughout the system and I was throwing a rear 02 sensor code, someone had also butchered the header flange trying to change the header gasket(which was still leaking) and took a little chunk of the block with it. My exhaust guy went over the entire exhaust system and replaced the mid pipe and muffler, replaced all gaskets including the header gasket, welded all leaks around the cats and 02 sensor mounts, remounted clamped and welded the heat shields and just for safe keeping I also did the 02 sensor simulator for the rear 02 sensor since I had a code prior to the exhaust fix and the cats which are on there appear to be after-market cats (which will throw a code in and among themselves). Code was fixed exhaust seems to work well.
When I start the motor she idles strong until warm up. After the engine is warm and I have been driving for a while I notice if I role up to a light at idle there is a subtle vibration and idle quality seems to fall off. It is not severe, just subtle and is also inconsistent. It does change more dramatically with weather conditions. Seems to be more prevalent when it is extreme warm or extreme cold out. The vehicle does not tend to loose power. There is no code. It is more of an annoyance but I do fear it may get worse. I also notice some valve clatter but my mechanic mentioned these motors are prone to this. Is this true? If true is it an issue or should I just turn the radio up LOL.
Any Help is appreciated!