I have read almost every thread associated with this problem.

Check Engine Light Flashing.
TCS light solid
Car hesitating. Noticeable loss of Power
OBII Diagnostic Test: P0303, P0305, P0306, P0300 (mulitiple Misfire), P1399 (Random Misfire)

I have 2000 TL with 205,000 miles. Where in the world do I start first. Could bad gas make all this trouble. My wife did put regular gas in the tank. Should I put in an additive to help. Change the plugs. The plugs may have about 40K on them. Seafoam? What route would you take? Would you do the most inexpensive first?

What are you thoughts because I don't know where to start?

 

when a single coil pack dies- it does exactly what you describe
Buy ONE coil at parts store or dealer, about 50 bucks

you can test for which coil by pulling the power lead, one at a time, noting when there is no rpm change,,thats the bad coil

Or start with the ones the ecu suspects- install new coil- reset ECU by pulling clock fuse on passenger end of dash (open the door) for a minute then reinsert fuse and start engine- all better? done!!
not better, move new coil to next suspected place, install and reset ecu
cyl numbers looking from front of car to rear- 123 rears 456 fronts

reset of ecu is critical on this job so it clears codes and forces a system self test

you are using the correct NGK iridium or ngk platinum plugs? not some other brand that cant handle our ignition system = will die very early

when down to half tank refill with 91,,there are people who use 87 all the time but it drops your fuel mpg, one mistake by wife isnt causing the current problem

seafoam if its time for the annual or semi annual gas tank method of 1 can to just under half tank - 8 gallons

 

Yes I am using the correct plugs. Do you think using OEM is better than aftermarket?

 

the oe plug was ngk platinum for 00-30 (99 used ngk iridium)

we can use gen3s stock plug= NGK Iridium,,or NGK Iridium IX as better choice than stock.
irid is a better metal and last longer, cost less than plat,

advances in mining technology brought the aircraft/race car iridium plug to the masses

you can buy them at most parts stores for 8 bucks each (average) while dealer gets 25 per plug for the same exact part!

on the coil it doesnt matter OE or aftermarket, never heard a bad word about aftermarket ones on here

 

Good to know. I have codes on 3 different cylinders. Will one pack solve the problem for everything or are we just doing process of elimination

 

When was the last time the valves were adjusted?

 

99% of the time when our cars throw ,multiple misfire codes its just one cyl. Find the one thats bad and it will fix the issue.

 

I don't recall having them done. Needs it?

 

start with the 1 coil,,,rare is the TL that needs 3 at once
chances are thats all it needs based on your description
note: coil often damaged during plug change by setting down too hard, treat them like fine china or some months later one fails out of nowhere!!

its often one of the cylinders the car suspects,,,code ending with 01 is cyl 1, 05 cyl 5
so you can do the quick diagnosis method by removing a power lead to coil and cking rpm change or not,,no change means bad coil

or remove the first suspected coil and install new one, connect back up, reset ecu!!!! and start car
runs better or it doesnt
move to next as needed

 

200kmiles= I would do the valve adjust after its running again
should inspect and adjust the ones that are off spec every 105kmiles according to the book

got to need the egr port and passge cleaning DIY by now,,good to do every 75kmiles
Intake manifold is off the engine (available for cleaning) for valve for adjustment job

 

It work like a charm. I tried the #3 cylinder and nothing happen. Tried number #5 and everything was working fine after that. Thanks for your help