I have a 2004 TL with approx. 145k. About a month ago, I've noticed that my car started rough idling really bad with my check engine light on, and at times, even flashing. I'd noticed a severe decrease in horsepower, along with a violent shaking that was prominent whenever my car was parked or stopped, plus it EATS gas, and has a strong fuel odor.


I immediately took it to the dealer, they checked it out, and told me that I had 3 of my ignition coils were bad, that I needed to replace all six spark plugs, i needed air/fuel sensors 1 & 2, and A new cat converter.


So yesterday, me and my friend replaced the ignition coils and spark plugs, but my car still shakes violently. Now, we tested the ignition coils by pulling out each one slightly while the car was running to see if it would make the engine stutter, which indicates that it is contributing to the engine's power, and the three front coils proved to be ok, but the three rear (which are the new ones) still have no impact on the engine, which indicates that there is no electricity flowing to those spark plugs. what should I do to get my horsepower back, stop the shaking, and stop burning so much gas?

 

check all 4 sensors thats on the pre cat make sure they're all tight

 

Try switching the front coils to the back and see if the results are the same. If the symptoms move to the front coils the maybe the new coils are defective. Are they OEM or aftermarket coils. Also check the wiring going to the coils in the rear, make sure no broken wires of bad connections.

 

I second that motion.