My 1990 LS 400 that I've had since new has been remarkably trouble-free after 160,000 miles until last week. The problem is that the engine seems to run out of fuel and the RPM drops way down but just before quitting it often will speed up and operate normally for a few minutes when the cycle begins again. Some times the engine will stop running but it always restarts with no hesitation so I was able to limp home.

Does this problem sound like a fuel pump or filter problem? At first I thought it might be a vapor lock but the problem now occurs on a cold engine.

I would much appreciate any ideas as I am 75 miles away from a Lexus dealer but close to a Toyota dealer.

Thanks for your help,

Ray

 

Sound to me like the fuel pump. I had the same thing happen with the same symptoms on a nissan that I had some time ago.

 

Throttle body cleaning suggested... with your mileage.
Here's an example.
https://www.clublexus.com/forums/sho...d.php?t=224751

 

Moving to the maintenance forum, from the LS400 forum.

 

I'd also check to make sure all the cam/crank sensor harnesses are in place and the igniter connectors are firmly clipped in.

 

fuel pump ECU?

 

Hello,

I had the same problem with my 1994 LS400. The symtom is that the car accelerates fine when you are easy on the throttle, but once you try to get on it ANY amount, it'll stall and almost die.

Since I work at a Lexus dealership, I was lucky enough to have the master tech look at it. I was informed that it's the ECU that's the problem. I got one from www.car-part.com and put it in a few days ago. After "breaking it in", all is well. Now I'm selling that car, since I just bought a 2002 GS300 Sport Design.

In short, I thought it was the TPS at first. Changed it and then the problem was still there. Unfortunately, It's the ECU that's causing the problem.

Hope this helps a bit.

Homer

 

For the 1st gen LS it's hard to pin point the stalling problem. I've seen the main engine ECU, the fuel pump ECU, bad TPS and recently one bad coil pack caused the problem. The weirdest thing is that the conditions are the same, but difference parts gone bad.

 

No trouble codes??

Jonny

 

In my original note I described 1990 LS400 problem as the engine seemingly running out of fuel and RPM winding down while driving and sometimes stalling. But never a problem restarting. Most of the time the engine would surge back as if the fuel supply suddenly returned which did turn out to be the case. There were no engine codes and the problem was intermittent and no fun to experience.

The local Toyota dealer in Hyannis MA (no Lexus dealers within 50 miles) cleaned the throttle body that he said was badly carboned up after 160,000 miles but that did not solve the problem and he gave up because during his checkout the car ran fine. While I was driving home the intermittent operation came back and I limped back to Toyota.

With the engine idling badly and going from high to almost stall speed by itself, the Service Manager (Brian Scarpellini, heard a faint clicking noise in the right front fender area that would come and go as the engine RPM fluctuated and be in sync with the surge frequency.

He found the clicking to emanate from the fuel pump relay however the relay checked out OK. He then disconnected the fuel pump resistor, also in that area of the engine compartment, and bypassed it with a jumper wire. The engine immediately smoothed out. He found that the resistor's resistance changed greatly as the unit heated up and he measured the local temp reaching 200 degrees.

Replacing that resistor completely solved the problem. It is P/N 23285-50010-LX. Unit price $63.28 plus $95 for labor.

I thank those of you who took the time to help and thought you might be interested in the final (I hope) solution.

Ray