Lexus ls400 1994

My mom owns a lexis ls 400 and is having problems with it sputtering. I have been trying the Internet with no good results. She has had it "fixed " two times, which did nothing. New spark plugs and a tune up, a new fuel pump and nothings working except spending lots of $$$. Do you guys have the correct answer to this problem???

Lexus ls 400 1994

The problem might be with carbon deposits on the intake valves. When this happens some of the incoming fuel gets absorbed by the carbon deposits and leans out the fuel mixture going into the cylinders. This then causes the engine to run rough or sputter.

You might try using a Top Tier gasoline to see if that removes the carbon deposits. If there are no gas stations that sell Top Tier gasoline in your area, then you can try adding a product such as Seafoam Engine Tune-up to gas tank to see if this helps removing the deposits.

Here’s how bad carbon deposits can form on the intake valves that can cause an engine to run rough.


We use the highest grade fuel and it still has this problem. Will try the seafoam tho, thanks.

A higher grade fuel doesn’t contain any more detergents than a lower grade fuel unless it’s a Top Tier fuel. So don’t waste your money on a higher octane fuel unless the engine requires it. And if you use a higher octane fuel in an engine that doesn’t require it, guess what can happen? Carbon deposits can form in the engine.


Ok, it says premium only. Will try Shell. Thanks! Any other suggestions out there???

SeaFoam is excellent for keeping older engines clean inside. My wife and I just bought a 1991 ls400 last summer, over 200K on it. My gut feeling is that your problem is a misfire. Either a plug wire shorted to ground or a cracked distributor cap. If your car is newer it may have a coil for each individual cylinder. Same theory holds as the coil extentions to the plug will short to ground in the spark plug tube. Possible deffective coil. If all that checks OK, maybe EGR issue.

Happy Motoring

PS. Top Tier Gas IS Best

There are lots and lots of suggestions that could be made. What you probably need is a good, local mechanic who will actually try to find out rather than just putting new parts on it. (Although you’re not losing with new plugs & if the fuel pump was the original you didn’t really lose there either).

Here’s a list of retailers who sell top tier gas. There is also lots of other good information on this website: