sixonemale

I have an 2006 SC430 with about 32k miles on it. About four months ago it stalled while my wife was driving it. More specifically, every time she started it, it stalled out. We took it to a Lexus dealer and it only repeated what it did once, not enough for them to figure it out. It also did not throw a code. Since they could not find the problem, they replaced the fuel pump after about week of trial and error diagnostics. I also had them replace the crankshaft position sensor based on another mechanics recommendation.

Today while driving along the coast with the top down, low and behold it did again, but this time I was driving. The car starts, therefore it does get enough electricity and fuel, but after idling at about 1,000 rpm's for around 5 - 10 seconds or so, it backs down to 800 rpm, 600 rpm, 400 rpm and then 200 rpm and begins to hiccup before cutting out. By no means am I an expert mechanic, but it seems like it may be related to an ignition coil of some sort, or some sort of ignition device.

Any thoughts on this issue, speculative or experienced based would be greatly appreciated. Thanks in advance.

Harold57

Did they replace the fuel filter? It could be a partially clogged filter, of course, if it is a clogged filter, I'd expect it to be a little lethargic also.

sixonemale

Harold, I suggested that several months ago, but they said it was a lifetime fuel filter not needing replacement. I still think that is a good thought even though it does not have that many miles, something could have clogged it. Thanks

harleydjce

The Lifetime Fuel Filter line is total rubbish!

Check your Owners manual and you will find it requires replacement at specified intervals.

I have a 2006 and it was just replaced by the Dealer as part of a normal Service

VVTiBob

Could be in the throttle body and/or MAF sensor. Although it's very odd that it's not throwing a trouble code.

sixonemale

Bob, Thanks for the suggestions. I considered those last time and again, they did not think either of those two items were the problem. I can only hope whatever it is, is no longer intermittent and will repeat itself tomorrow for the mechanic(s).

scyul

That would also be my first guess... Had a similar problem on a Subaru SVX.
I'm sure it's not the fuel filter!

specialist

You may want to check / clean the IAC and throttle body. I know on one of my prior cars it would do this when idling, and it took cleaning them both to get it working properly. Turns out there was a bunch of buildup on the valves that caused them to stick, and that was causing the idle issues. There were no CEL lights on that car either!

sixonemale

Thanks everyone for all the very good and well thought out suggestions. This was a very difficult problem to diagnose since it was extremely intermittent. I received a call from Lexus today and they stated that they had absolutely found the problem and even took a photo of it. It was fuel pump resistor that had been shorted or was simply a bad resistor that had burned or melted. I have yet to see the photo, but for the those interested I've attached schematic drawing with actual drawings in the attachment of the SC430 fuel system. Needless to say I'm very happy to pay Lexus for solving this problem!

Bon

FWIW: It looks like the fuel pump is a two speed motor. The resistor is used at low rpm's and the fuel pump relay kicks the pump into "high gear" at higher engine rpm's. This gives a more consistent fuel pressure throughout varying engine speeds.

specialist

That is one I wouldn't have guessed! Glad to hear they found the problem. The real question now is why did that part burn out? Hopefully they are tracking that down so it doesn't come back.

sixonemale

Specialist, I fully understand and appreciate your thought that this could be another symptom and not the problem. I called them earlier today and asked them to ensure that this will not happen again. In other words, was it a bad resistor vs. some other problem causing this symptom or the resistor to melt.

VVTiBob

I'd also ask if they know why DTC were not stored in diagnostic system.

specialist

Sixonemale,

I'm glad to hear they are looking for potential root-causes.

My wife had a 2003 VW Passat with the same problem. The dealer kept throwing parts at it and it kept coming back. Right after she and I started dating, I pulled the thing into the garage and found out that it had an old school distributor cap that was cracked. Every time it would rain the engine would die. 20 minutes later and about $30 it never happened again. She'd spent over $1,200 at the dealer trying to fix problem.

It's not only inconvenient, but also dangerous. Good luck with the fix!

sixonemale

I just received a call from the Lexus service manager and because there were loose pins and/or connectors near or around the resistor, that's what caused it to over heat. How they became loose I do not know being the second owner of the car. The mechanic assures the service manager that the problem has been solved. He also said the reason it did not throw a code, was because that particular circuit is not connected to a circuit that would register a code.

Again, thanks for everyone's thoughts regarding this difficult intermittent problem that I now consider to be solved.