hi all,

I've searched the boards but I haven't ever seen anyone mention this: my '98 GS400 (about 35K mi) will produce knocking (precombustion) sounds when the throttle is applied quickly and the engine is reving pretty low (around 2000RPM or less, but it can happen at higher RPMs, too.)

Try this in your GS: roll your windows down, coast the car at about 15-20 MPH and then gas it hard. Does your engine knock, especially before downshift? Mine does! I've been filling the car up on premium (Chevron) since I've owned it, and I've experienced knocking even if I fill up at different stations. Do I need to run race gas?!

I spoke to a guy named Chris at Tustin Lex and he said that knocking, especially before a downshift, is normal. They reset the ECU and it seemed to help a little, but now it seems to be knocking as much as ever.

This is bad for the engine, despite claims I've heard that the engine is indestructible. Nothing mechanical is indestructible. Do the technically knowledgable among yous have any ideas what might be wrong? They claim that the engine's knock sensors should retard the timing upon detecting knocking, but this has been going on for a while. Should I try (yet) another service center?

(and when are the Socal members having that Sept meet? )

Thanks for your advice!

 

My 98 GS400 never did it and NO, I don't believe anyone who says it's normal. Sounds like major BS to me.

Take it to another dealer and have it checked out asap.

 

Thanks, Marty. Hmm, the only thing is that the GS400's engine is so muffled that it's often hard to hear the knocking... You really gotta be tuned into it, and it's next to impossible to hear with the windows up.

Call me crazy, but I don't think I've ever heard engine knocking until I brought the car in for service a few weeks ago. They were messing with the throttle body and the engine ECU to try to correct for a low idle. I've had the engine ECU and throttle body replaced since then (by another dealer). Of course, maybe I just didn't hear it until then, who knows? The idle is still too low when engine is warm and A/C is off (around 450 RPM, you can feel the vibrations due to the low speed), I wonder if it's related?

AGH, this car is driving me CRAZY! So many friggin' problems!!!

 

My G3's RPM runs around the same rpm. and it does knock around when I start my car for about 5 seconds while the car shakes a bit... the computer's been changed already... dunno what else to do... the car runs fine afterwards..

~manny

 

Bro

I think your knocking is caused by improper engine timing. I had this problem before. The computer regulates timing and this can easily be checked and corrected. When you go in for service ask to see the service manager and explain the problem.

A lot of the guys that write your ticket don't know jack about the cars....they are just punching the clock. So get with the service manager and be persistent.

Later

DZMAN

 

.

 

I get the same problems and I also have the low idle at 450 rpm

 

I have a 2000 GS3 and mine does it too. It seemed to have started after I took the car in for the 15,000 mile service, and didn't notice it since it was the summer and the A/C was always on. Sure enough, I started to notice that there was a knocking/pinging on low speed accelerations only some of the time. Been consitently using 93 octance fuel.

Took it to the dealer, and of course it didn't happen during the little test drive I did with my service advisor. Later he told me it was normal for these engines. Really? I have been in many other cars, of much less quality than a Lexus, and have not had this problem. If it was only a small amount, it would be OK, but it is pretty consistent, and rather loud when you actually hear it.

Please post if anyone finds out anything. I have to take it in soon anyway...

 

Hey all,

I got this information from 2 separate Lexus lead techs:

The engine ECU will detect knocking via the engine's 2 knock sensors (applies for both V8 and I6 engines, though I'm not sure how many knock sensors the I6 has). If it detects knocking, the ECU will retard the engine's timing, apparently reducing performance somewhat... this is why you can (but should not) run regular gas in your Lexus; the ECU will detect crazy knocking and retard the timing significantly, reducing performance to protect the engine.

If your knock sensors are jacked or otherwise off-line, you'll get a CEL (check engine light). Generally, all the dealers will do is reset the ECU, and *perhaps* clean or replace the throttle body. The throttle body is also routinely cleaned/replaced to help correct for low idle, though mine was completely replaced and it still idles at a throbbing 400 RPM (warm engine, A/C off) sometimes.

One of the techs said that this is just a fact of life for these engine/tranny combos. He said the old LS400's knocked so badly at low RPM + hard acceleration that the owner's manual had a section describing why it occurred.