BenjaminA

So my LS started doing something that has me a little nervous. I'll be on the freeway in 6th gear at around 65 mph. The rpms will be around 2k. I'll go to accelerate slightly and the car begins to shake. Almost feels like when an engine that's running rough right before it cuts out. The shaking gets worse as I increase the throttle position. It does it until I really put my foot down and changes down a gear and the rpms go up. After it changes down to fifth its smooth again.

At first it was it was only in top gear on the freeway at around 2k rpms that it would do this. But now I'm noticing it in other gears when the engine is under load at lower rpms. Again once it changes down a gear the rpms go up and it accelerates smooth again.

I don't think it's transmission slip because the rpms aren't jumping around like crazy when the car shakes. It doesn't do it all the time but now when it does shake it gets a lot worse. No engine codes yet or anything. It still accelerates at an acceptable rate too, just shakes like crazy. I feel it in the seat and around me, not in the steering wheel at all though.

It almost feels like a really bad misfire or the fuel is being cut, but again no engine codes. I cleaned the MAF and ran a thing of fuel cleaner in the tank. The strong type cleaner we get here at the shop I work at.

Anyone experience this issues before? And it's a 2006 with the 6 speed about 98k miles on it too..

smokey6010

Do an OBD check on it to find out which cylinder or cylinders are causing the problem. Ignition problems show up when you put a strain on the engine.. Sounds like a bad spark plug or coil.

BenjaminA

It has yet to throw a check engine light code though. I did pull one spark plug out and it was an NGK iridium that appeared to be fairly newer. So the plugs have been changed before.

smokey6010

I would still do the OBD check and look for any stored codes.

StanVanDam

Just curious if you ever cleaned your MAF or used fuel cleaner PRIOR to this problem occurring. There is anecdotal evidence that doing these 2 procedures can cause more harm than good. Maybe your fuel cleaner dissolved the nylon fuel filter "sock" and fed dissolved nylon through your pump and injectors. Or maybe you have a leak in a fuel rail, or perhaps the MAF cleaning wasn't effective and caused send incorrect airflow data to the ECU.

To diagnose the problem properly, you need an OBD2 reader, preferably Techstream. Check your live engine data, such as short-term and long-term fuel trims, fuel flow and injector data, misfire counts, MAF sensor temperature and air flow rate, check your transmission solenoids, etc, and then you can see what the problem is. There are some engine codes that won't activate the MIL right away, such as when it is a recoverable error or when there a certain number of failures are required to activate the light. The system keeps history of past codes too, which can help in diagnosing the problem. Don't do a code reset because this will erase fuel trim and other helpful details.

BigBoomer

Check yer engine mounts. I had a similar feeling on an S-class and one of the engine mounts had completely separated.
At low RPMs under load it would shake like a dog with a new toy. Once RPMs came up it smoothed out, regardless of what gear you were in.