I have had a problem beginning when my mechanic said I didn't need to replace plugs at 100K miles if it was running good. I was occasionally getting a lean code error but I didn't replace plugs per his advice.
At 105K the car began to run rough and a couple days later stopped runnig as I got to his garage. He diagnosed misfires and replaced plugs / coils.
Two days later check light came on again signaling cat converter error.
New mechanic replaced ox sensor first and then cat converter. Light out for 3 days.
Light back on and signaled thermostat. I fixed that.
Light on showing lean issue now /again. Cars been in the shop and they haven't fixed it yet!

any suggestions on the threat is errors or current problem?

 

Welcome to the forum.

Can you please post the 5 digit fault codes, such as P0301, etc.? The generic definitions you were given are always accurate.

Do you know what brand of coils were installed? Many forum members have reported trouble with off-brand coils, such as Chinese specials on eBay or white box units from discount chains.

 

+1 on Karl's advice.

Which engine is fitted to the vehicle?

Were the cam cover gaskets and spark plug boss seals also replaced as they tend to leak oil into the spark plug wells and cause misfires.

 

Just noticed a little goof in my reply. I meant to say "The generic definitions you were given are NOT always accurate."

This is not an admission that I was wrong less correct than usual.

 

I wasn't able to find any OE Denso ignition coils, so I got some NGK coils(made in China of course, but to NGK's specs, not to be as cheap as possible) for my 4.2, the car runs great, now that I replaced all of them. Most things are made in China these days, but the important thing is the customer's specs. If they want cheap **** the customer will get cheap ****, if they want the best, then they'll get that too.
I had a couple coils go out one at a time and just replaced those. But when the third one threw a code, I broke down and replaced them all. I read a warning here on the forums that bad coils will ruin the cats, as shown here they do and at least I replaced mine promptly. Even with all new plugs, but with coils of different brands the engine on my car wasn't working quite right and the tranny wasn't working right either. The engine and tranny are so interconnected in these cars, if there's a problem with the engine it will affect the tranny also. In the owners manual it says to change spark plugs, but not the coils at 100,000 miles. But if you want to keep your car, just break down and change them all, especially if the coils start throwing codes and you're good for another 100,000 miles. I found that the cheapest place to get them was NGK's website.