I have been have an off and on issue with my 04 MCS. Out of nowhere I get pinging and an occasional lopping idle. Then the pinging will go away and not be able to be replicated and the idle will be smooth as silk. Then a couple days later it will ping again. Now I am not pinging but on hard acceleration at around 4000 rpms and up I am getting multiple stumbles. I will be accelerating hard then for a split second it will stumble then pick back up again. Not sure if it is misfiring (no codes at all) or whats going on. There is no fluctuation in my boost guage when this is occuring. As I am accelerating my car instantly boosts to around 13psi then climbs to 15,16 or 17 depending out outside temperature. When I feel this stumbles the boost needle doesnt fall. I have gone through 1/2 tank of gas with lucal fuel treatment to see if I had a dirty injector but that doesnt seem to help the stumble at all. I am going to be checking the plugs this weekend to see if there is any problems there. I have checked my plug wires and they seem good. Ever since I have had the car it has had the occasional loppy idle, and for some reason I have had the occasional pinging, but never a high rpm stumble. Thanks in advance for your help!

 

Are using 91 or 93 octane gas? If not this could be predetonation caused by inferior gas

 

91 Octane. Right now I have in Mobile. I usually use either Shell, Mobile or Chevron. Whats strange is that the other day it was 113 degrees and no pinging. Then with the same tank of gas on a different day at 85 degrees it will ping. Then the pinging will just go away???Freakin wierd.

 

I've felt a similar minor stutter, or stumble since I've picked up the car. Very minor and not all the time, but I notice it at steady speeds on the highway.

I think it's the drive by wire switch being very sensitive to minute changes in foot position. Which is why you don't get any missfire codes etc. since it's just doing what you're asking it to do.

I don't have any data other then some experimenting while driving, perhaps you could test it by using the cruise control under the same conditions you've been having to issue to see if it still occurs.

 

My problem is occuring at full throttle...completely smashed to the floorboard.

 

I don't see a problem with setting your CC to full throttle

It could still be the DBW but that's still just a guess on my part.

 

I used to get the stumble upon starting the car. Software update at the dealer fixed it up completely....until about a month ago. Now I get it to a much lesser degree and not on every start up. Summer gas maybe? I use 93 octane, but it does state that it can contain up to 10% ethanol.

Ken

 

I dont have cruise control

 

if it was the belt slipping I would see a fluctuation in the boost gauge...right?

 

I'm also experiencing the same misfire/stumble at WOT, primarly occurring during WOT in 2nd and 3rd gear from 4000 rpm- redline. It almost sounds like wheel spin.

I do not know what knocking/pinging sounds like in a MCS; although I have driven a 1992 Buick Park Avenue that had a bad knocking problem, and it didn't sound or feel anything like what I'm experiencing now.

Maybe someone else can help us out...

 

I dont think its wheel spin. I wish I had the whp to have traction issues when I hit the gas on a 50mph roll.

 

Just check your drive belt and drive belt tensioner visually. Run fuel injector cleaner on your next tank of fuel too.

Jeremy