This morning I went to the store. I had planned to take the freeway instead of the close grocery store as it is Sunday and the traffic would be lite. I always use the 4-5 minutes it takes to get to the freeway to let the car warm up to proper temp before doing anything aggressive.

This time right before I got there I noticed the check engine light is on and its running rough. I pull over, rev a few times to assess the rough running then shut it off. Wait a minute then turn back on. CEL is still on but idle is back to normal. I get on freeway and give it some gas and roughness comes back.

I get it home and use code reader and first time get P0300. I reset and restart. CEL gone and car is back to peppy revs. I go for a drive and everything seems fine till I go WOT and at about 4500 RPM CEL comes back as the car sounds like something like a wastegate or ?? comes open and power drops off rapidly.

I have repeated this 3 times. Reset codes/CEL go for drive everything is fine as long as you do not let WOT go above 4000 RPM then CEL comes back and the wastegate or whatever opens losing power. Idle after that seems like it is missing or at least rough. No backfire, smoke or anything else seems off, but I did notice the engine seems very hot yet the temps are all good. In taking off engine cover I almost needed rags it was so hot and its maybe 50 degrees out. Also, the engine fan is coming on at engine start which I have NEVER heard it do in the 8 months I have owned the car.

Could it be that IC pump?

I know that P0300 is missfire. Coil Packs?

ideas?

Car has 34K on it.

Could be a combination of things, def coils are done and need changing, i would do both.

Also the heat exchanger needs to be looked at.

All very predictable..

Check the part numbers on the coils. 34k is lite for new # coil packs but not impossible. Did it give you anything other than P0300?

Thanks.

Yes, it gave P0303, 0403, 0703, 803, 903. But I think the other codes were from the missfires making the computer crazy.

Can you post a pic of where to check the part numbers on the coil packs?

oops

they are posted on the top plastic cover towards the front of the car.

On my 2005 SL 65 with 40K miles I checked the following after misfires as you describe:

Cats - ok
Crank position sensor - ok
MAP sensors - ok
Coil packs - ok

Plugs - changed - 5 years old and should be changed regardless miles (manual)
Misfires returned after a day....then I checked the Ignition module....BINGO

Ignition module - replaced....this was the real culprit.....sits on top of the engine
Intercooler air temp motor replaced...
covered under warranty - $ 1,100 part.......no issues since.....

Check that ignition module which regulates the voltage to the coils.......

Thanks. I got my eye on that ignition module.

Can you see them without removing anything?