LS4Lexus

When I'm waiting at a traffic light, I can feel the car shudder slightly every now and then. Since the RPM dips down momentarily when the car shudders, I figure it must be the engine that's stumbling.

Any idea what the problem might be?

'92 LS - 100K miles

ChuH

Without knowing some history with your car it is very difficult to help diagnose this problem. When is the last time you changed your air filter and spark plugs? Does the problem occur when your A/C compressor kick in? Does the problem occur when you come to a stop?

Chu...

LS4Lexus

Air filter changed 8K miles ago. Spark plugs changed 20K miles ago.
I can feel the shudder when the engine is idling (e.g. waiting at a traffic light) even when the A/C is off.

Inabj2

Mine does that I have a faulty egr system though.

purebliss

I would check the Fuel pump or the fuel pump relay fuse.

Lexusfreak

IT wouldn't hurt to change the PCV valve & fuel filter & make sure the timing is correct. Some fuel system cleaner might be wise too.......Chevron with Techron stuff is fantastic.

ServiceGuy

I would check the i.a.c valve -

LS4Lexus

The fuel pump and fuel filter (OEM) were replaced a year and a half ago - this was after the engine shut off on its own when coasting at a low speed. Hopefully it's not the same thing, as that was an expensive repair!

Thanks for the suggestions. If anything else comes to mind, please post.

Lexusfreak

What about the PCV valve? Have you ever had the throttle body cleaned?