This is on a 98 GS400 with ~130k miles.

The shaking started after pumping a new tank of gas at a shell station. When stopped at red lights the engine would starting shaking and feel like it's going to stall but no CEL. The tach needle stayed steady during the shaking and did not jump or dip. This stopped for about a week but came back last friday. When I was almost home the CEL came on and started flashing and the VSC came on too. Once I got home I turned off the engine and started it back up and the CEL and VSC went away.

I did some searching on here and cleaning the TB and MAF was a good starting point. Half way through this process the CEL and VSC came back on but after finishing I reset the ECU and they both went away. The shaking was gone so I took it for a quick drive. Just when I thought that fixed it the shaking returned but no CEL. Needing to go out of town that night I left it as it was during the whole weekend.

This morning on my way to work sure enough the shaking started again. What I notice is that it starts only when the engine is warmed up (maybe ~15 mins of driving). It would also shake for 2-3 seconds, stop and then shake again for 2-3 seconds. Tach needle stays steady the whole time.

Since it's not constantly throwing a CEL I don't know if having autozone or kragen do a scan will show anything. Also I heard they no longer do free testing? Hate to pay ~$100 for the dealer to just run a few scans too.

 

someone around here should have a scan tool.. where u located?? 1st thing u should always get the code then delete it to see if it comes back

 

I'm Pomona (SoCal). It'd be great if someone here does.

 

If the CEL was flashing it's most likely a missfire, usally caused by no spark, which could be:

Spark plugs
spark plug boots
coil pack

Also I would run fuel injector cleaner through it if it just started after a fillup.

 

That sucks, If you were here in Nor Cal I would help you out. If you can not get the code checked for free buy a Generic OBDII Code Reader. They can be had real cheap many places, Harbor Freight has one for $40.00 right now. The auto part stores probably have some in the same price range.

You can also post in the regional So Cal forum to see if someone around you has one.

 

Shell is bad gas. Screw the owners manual.. That is why HPFP's are going out on some BMW 335's. I use Mobil in all of my cars with no issues.. Drive that car hard and re-fuel with Mobil.

 

I seriously dont think gas is your problem....I had the same problem a few months back and believe or not it was motor mounts, they appear to be perfectly fine from above but once you jack the engine up youll meet your culprit or culprits....

 

i was just fixing to say check your motor/tranny mounts. when u start the car up does it shake just sitting idle? what about in drive but not moving?

 

Ok, I think I got fixed. Thinking it was a misfire issue I pulled all coil packs and checked the plugs for fouling. A visual check through the plug holes showed they were all clean. I was about to put everything back but decided to remove the plugs and check the center electrode since I had everything apart already. I was shock to find 2 or 3 of the plugs extremely loose. I re-tighten all the plugs and let the car run at idle for about 10 minutes. Not one shake. I put everything back and took it for a test drive and everything was smooth as butter. Drove it to work today and again no shake so it was definitely the loose plugs causing a loss of compression.

So in all, $8 spent (fuel injection cleaner) trying to fix the problem.

 

Interesting how people don't torque down the spark plugs...

 

some of the wierd problems on the GS...are not even that bad at all... like that guy with tranny issue... alll he needed was a new battery WTF>..

 

I got the misfire recall and had my car pistons fixed at the Beverly Hills dealership. This was about an $8K-$10K job and it was a voluntary recall by Lexus.
After running fine for 4 years, my car started to stall while driving. I spent 3 years driving the car this way and just dealing with it. I had the engine clean out done. Transmission inspected. But nothing seemed to work. I took it back to the dealership and had them run a diagnostic exam for $219. They gave me a list of things that needed to be replaced (mass air flow meter replacement, air filter replacement, oil change and new ECM. I did everything except the ECM, but the car still ran poorly. I finally found a used ECM on ebay and bought it for $200. I had my mechanic install it and the car ran like it was brand new! No more stalls as I come to a stop, and no jerky movement anymore. Also, the car did not stall when I was on a hill. In the end it needed a new ECM (electronic control module).