My RL has been shuddering the past few weeks. The symptom is a shudder or shake when on the highway around 60 mph or so, if I let off the gas and then reengage the gas pedal, the car would shudder before smoothing out. The car does not shudder if I am accelerating at a constant, only when I let off the throttle and then reapplying it..and it seems to only happen at 55-60mph range.

Some background: This happened previously but would happen even at 40 mph, and the check engine light would flash and blink and then goes away. I ended up changing the 3rd and 4th transmission pressure switches, which did not help. I then changed the ignition coils and it fixed the issue for a week.

Fast forward to now, the car idles smoothly, the shudder happens only at 55 mph + when gas pedal is engaged and only a couple of times, as if it is hunting for gear or power loss. This time however, there is no check engine light flashing. Any ideas? This is a 2008 RL with 133k miles. New ATF fluid. Always on top of maintenance.

I have put a lot of money into this car and would hate for this to end. still loving the RL.

 

Check for bad CV joints

 

why did you change ignition coils?

 

I hate to say it but this sounds like torque converter shudder. Hopefully that isn't the case but it does sound like it.

When is the last time you changed the transmission fluid?

 

the first time around there was a shadow cel code for misfires.

 

I change it every 30k. last time was a few weeks ago.

 

I ask because if there is a valve cover leak you will get a misfire, which could cause a shudder

 

that's what i am thinking too. worn or bad inner drive axles. i plan on buying used oem ones on ebay. if that fixes it, i may invest in new ones unless someone can recommend good aftermarket ones.

 

Hey just a theory: The knock sensor can trigger shuddering too.

Low level engine oil can trigger it. But i don't know what else can trigger it. Maybe too much O2, but uncertain.

 

Just to keep everyone posted. The shudders still happening but then i've started to get misfires. I've recently replaced the spark plugs and coils, so I am trying other things. I took the valve cover off and see a lot of carbon. I am cleaning the EGR and ports today. Any other things I should look into?

 

were the coil tips covered in oil?

 

Yikes. Looks like you're using the Torque app? I love it.

 

have you check the EGR valve being stuck?

 

nope. none at all. the spark plugs, however, shows white tips. car must be running lean.
yup! it is an awesome app!
yup, i am cleaning the EGR right now. a lot of carbon. going to put it all back later today or tomorrow and put in BG 44k fuel cleaner and see how it goes. if it isn't the spark, it must be fuel or leak. i hate misfires lol.

 

well folks..I may have fixed it but hoping it will be permanent. I cleaned EGR valve and ports with throttle body fluid. used my shopvac to blow the carbon out. I also cleaned the MAS sensor. Replaced all spark plugs even though they were replaced only 15k miles ago. I noticed they were loose. so, i tighten it down till it is snug but definitely a little over 22 ft lb. Lastly, i put some BG fuel cleaner in.

No shuddering or any issues so far. Will update in a week or two.

 

I think what happened was the spark plugs were loose and so it ran lean. Also, I noticed the tips of the spark plugs burned off..so due to the lean condition it probably ran too hot and burned off. thanks everyone for helping. hopefully this is a permanent fix because I love this car!! clean your EGR valve it is very easy to do!


ran too lean and tip burned off


EGR valve was full of carbon.

 

Careful with the spark plugs, on J series its kinda common issue for the plug to come loose and shot out the plug hole and its usually happen with plug #5.

I hand tighten mine a little more than snug its more like 50 ft/lbs, I never had any issue with it being loose tho.

 

Thanks, Truong! I set it to 22 ft lb and then another quarter of a turn, but based on what you're saying, I will check it again and torque it down some more this week.

 

Update for people interested. My car has been acting up again. It stumbles for a split second or two and shakes violently like loss of power around 55 mph to 60 mph intermittently. I replaced the axles with Raxles, thinking it was the problem, but it isn't. So, today I decided to look at the spark plugs and low and behold, the electrode tips burned off in cylinder 2, 3, 4 and 5. From researching, it might be due to lean condition.

I replaced the pcv valve, egr valve and the spark plugs just now. I know it will fix the car temporarily but I need a permanent fix. Any ideas as to what's causing my car to run so hot? I ordered a fuel pump and will replace that soon
Also, I noticed my coolant reserve tank was empty even though I just filles it up 10k miles ago.


new on left. old on right. notice the tip of the old one.

 

Based on those plugs, and the fact that it seems like you've checked all the air supply, I'm guessing it's a fuel issue? Have your checked the fuel pressure regulator?

 

Not yet. I ordered a new fuel pump that should come with a new pressure regulator. Hope it gets here soon so I can replace it. Car drives great right now with new plugs.

 

What about O2 sensors?

 

Good suggestion..Should I replace all of them or is there a specific one that is causing my lean condition?

 

Nevermind. Found the answer. Upstream sensors on bank 1 and 2 are the ones sending the air fuel mixture to the ecu, so that's what I plan on replacing.

 

Usually a code comes up when they go bad. But I have no experience on whether they may go bad without triggering a code.

 

By the way, I have also felt a little shudder sometimes that resembles when, if you were driving a manual, you have slowed down on a turn, but try to pull after the turn on 3rd gear... the car kinda shudders but tries to make it on 3rd gear..

I dunno if this can happen on higher speeds..

Also check for any cracks in the manifold, and clean that rotating thing inside when you take it out. Carbon accumulates there too.

 

02 sensor can goes bad before throwing a code, there are specific parameter reading on the o2 sensor before trigger the CEL. I would buy the Denso o2 sensors and don't forget to reset them once installed.

 

Thanks for the suggestions by members here, I finally got around to replacing my O2 sensors today. I will monitor the car for the next few months to ensure the car doesn't burn the spark plugs again due to lean condition.

The install itself is pretty easy if you have the right tools. I bought both Denso sensors on RA.

 

Good work on your troubleshooting so far! Another idea in case it comes up again is a Valve adjustment! Also look at your long term fuel trends. That’ll be your indication on weather it’s fixed. Is this happening on all cylinders? Or just a select few? Also when you did the coils and plugs, did you look at the valve cover? On mine one issue I had is the coil started arcing to the valve cover. It started eating away at the metal. Had to replace the coil.

 

Thanks. Yes, valve adjustment is definitely on the table if the new O2 sensors does not resolve the issue. It did not happen on all cylinders, but on 2 and 5 most of the times. I replaced spark plugs a few times already, and four of the six plugs' tips were burned off. I have replaced the coils on all cylinders so I do not think that's an issue. I'll be sure to give everyone an update. However, given that I am in WA and the covid crisis we are in, i am not driving as much, if at all.

 

I had the same problem with my 2008 RL, shudder on the highway driving 60 mph.
I took the car to Nick, he found the problem to be spark plugs.
Looks like there are counterfeit NGK plugs on the market, the tip burns quickly like you described.
I searched online and found some videos. here is one

 

I bought some NGKs on Amazon that were counterfeit. Developed a bad shudder/miss after 30k. It didn't give any miss fire codes and I spent a long time figuring it out.