perhaps you connected your spark plug wires incorrectly check your firing order if you crossed a couple of spark wires the engine may still run but very roughly also you may have spark plug wires that are not fully connected to the plug are you reusing the old plug wires may be time for a new set check connectors for corrosion recomend using high quality spark plug wires
iridium plugs are made to last 100,000 miles
Common problem with this engine is the ignition coils.
I have a friend with 170,000 miles and he still drives it daily, I have another friend replacing his engine at 50,000 miles.
Gear oil should be changed every 4,000 to 5,000 miles. Motor oil should be changed every 3,000 miles to keep the engine running clean.
120000 miles with original iridium plugs.
=It has a belt. The belt must be changed every 60,000 miles. WARNING:==This is an interferance engine. If the belt breaks there will be serious engine damage.=
The engine oil should be changed every 3000-5000 miles
Could be in need of a complete tune up. Does the check engine light come on?
Mobile 1 engine oil can last up to 15,000 miles. However, it is recommended that the oil is changed every 3,000 miles.
When my 2002 SC2 sputters, stalls, "Service Engine" light comes on, I dump a can of injector cleaner in the tank and it runs fine and the light goes out. Can't say for sure that's your problem, but it is a small enough investment to try it out. Good Luck.
You cannot tell by looking at it. For this reason it must be changed at a set time period of miles or years. Without knowing the make, model, engine, & year I cannot tell you when it should be changed. Warning: If the engine is an interference engine and the belt breaks you will have internal engine damage.
I just spoke with a Parts person at a local Toyota dealer. He told me that the 2004 Toyota Matrix requires Iridium spark plugs, which retails for about $12 at the dealership, and it should not need to be changed until 120,000 miles.