Sc 400 Hesitation...?

[92Lex]

Yeah, removing an EGR will improve performance somewhat...MPG will decrease slightly. It's not going to cause damage without the EGR but just make sure you plug it back in (and make sure it's functional) before you go back for your bi-annual smog check.

[KCTalker]

Was your tech implying that this car had this problem when it rolled off the dealer's lot. It seems odd to think that people drove around in new $50k SC400's with chronic hesitation problems. When I first bought my car this wasn't happening. Didn't feel this until just after 100k. Is this just an alternative bandaid to buying a new EGR valve? Do you think a new EGR would clear up the problem?

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Hey BMAN,

Here's an update. Along with the EGR gasket-mod described above, the tech also obviously reset the ECU during the repair ('cause all the radio presets were gone when I got the car back!).

I complained to the service rep that the car wasn't much better, but as another poster noted earlier, the car runs flawlessly when ice cold. I made the same argument that you did: namely, this car would have been a failure if everyone who plunked down $50K for it when new had this problem. But the service rep insisted that all '95s have this problem. He also said he'd check with his technician and find out why the car runs perfectly when cold.

After this, I kept driving the car, and after about 2-3 days, its performance improved quite a bit! I was shocked! I can only attribute this to the re-set ECU, "learning" not only my driving, but the requirements of the re-configured EGR.

Today, the Lexus service rep finally calls me back. He says that his technician reports that (get this) the EGR valve has a built in *heat sensor*, and so doesn't kick in until the car warms up! Ain't that a kick in the !Removed!! It also implies that replacing the EGR valve, as you suggested, wouldn't accomplish anything.

My feeling on this--as actuallly suggested by the Lexus technician during my check-ride with him--is that the problem is actually upstream of the EGR valve. Why is it acting so stupidly? Doesn't the ECU control its behavior? Would replacing the ECU fix it? Or is the ECU getting bad signals (as someone else here implied) from bad O2 sensors? I mentioned all this to the service rep, but he disagreed with me heartily.

Meantime, my car is running the best it has since I've owned it (only stumbles about 2% of the time), so I'm pretty happy.

It's night-time as I'm posting this, but I'll snap a pic of that EGR connector for you and post it tomorrow.

I hope my admittedly low-tech feedback helps anyone out there!

[KCTalker]

Here's the promised pic (if I manage to upload this properly!) of the EGR valve connector. It's that light gray plastic piece above the arrow.

[Skydiver]

Here's the promised pic (if I manage to upload this properly!) of the EGR valve connector. It's that light gray plastic piece above the arrow.

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Thanks for all the great info and the pic. Here's a few tidbits (my own War and Peace) from my own recent experiences with my 95SC4. I notified my local Lexus dealer of the hesitation issues. He suggested a very expensive 60K tune up and fluid replacement service, and to add a throttle body assembly cleaning. The tech who worked on it has been a Lexus tech at this dealership since 1992. He said that the SC4's engine was indeed redesigned for the 96 and later models. He explained why the service for 92-95 models is MUCH more expensive than for the later models. It's because, when servicing the older units like mine, Lexus REQUIRES the valve covers to be removed and valve clearances to be checked and reset to factory tolerances. For the 96+ SC4 engines, the shims and their mounts were redesigned to be more consistent long term (maybe the ECU/EGR were, too?). So the techs only 'listen' to the covered valves when servicing the 96 &+ models, and will then remove the valve covers to service the valve/cam assembly ONLY if they hear an audible ticking. This saves an hour or two of labor plus the cost of the valve cover gasket(s) for 60K services on the newer models. Upon completion of this service, I experienced some improvement to the hesitation issue on my car. But it's still there, still noticibly after the engine warms up in warm outdoor temperatures. So the service did not eliminate the issue. The tech then stated (as you were told) that this hesitation issue is a problem common to this engine (thanks, great timing). He did not say if it was true for all years 92-95, or just the 95's. But he came as close to admitting a design flaw as he could without outwardly dissing his company's product. I thought this was the same engine as that installed in the LS400s of the day (if anyone knows differently, plz let me know). I cannot imagine how a design flaw of this magnitude across both models could not have been documented as a service bulletin at Lexus, not to mention corrected in a recall.

Other comments from the tech on this model which are not related to hesitation, but might be worth sharing:

On occasion, owners of this car may encounter a 'burnt' smell when operating the vehicle. He explained this is odor from the sprayed on underbody treatment being seared by the extreme heat from the catalytic converter. Could this heat also fry the underbody mounted O2 sensors eventually? Although the same tech told me it's unlikely (since his diagnostic showed my O2 sensors are 'ok'), I may yet try replacing them. Although the sensors may not have failed enough to trigger a diagnostic code, they could possibly be impaired and be sending erroneous data to the ECU, which in turn could contribute to its poor control of the EGR. I'll then reset the ECU, and keep my fingers crossed.

Items known to be failure points on this car: rack and pinion steering, undersized brake pads which require frequent replacement (always use expensive factory pads to avoid squealing)

Items that are robust and tend not to fail: A/C, Tranny, Engine overall supposedly good to 200-300K

[KCTalker]

Hey, Skydiver:

Thanks for the info; now I've got a tidbit for you which you (and perhaps others) may find interesting.

I've always believed in the old adage that you should never buy a first-model-year car, because it's still got the original bugs that would have been worked out in later years. Indeed, I read numerous complaints about the very first SC400s (was it '92? pardon my memory lapse): everyone carped about the emergency brake lever, and how it dug into the driver's right leg. Bingo: the very next year, Lexus revised the emergency brake lever so it wouldn't hurt anymore.

Naturally, then, I figured I was pretty darn safe buying a '95 SC400, since the model had been around for a few years. But recall that this hesitation issue stems from the EGR valve. Well, dig this:

I downloaded from Lexus the "New Features" document for the 1995 SC400 (it was originally used, I'm sure, to educate the sales reps), and guess what it says? Allow me to quote:

"1UZ-FE Engine

On all models, a step motor type EGR valve is used, and the cold start injector has been discontinued."

Ha!

So it's not a first-year car, but it does have a first-year EGR valve! #$%^&*!!!

Good chance its bugs were corrected in '96; this would also explain why so many Lexus service departments are familiar with the--yes, I'll use the phrase--design flaw on the '95.

Thoughts, anyone?

[jzz30]

i can agree with that because my 93 doesnt hesitate. and well in 96 didnt the motor change a little? it went up in HP too, to like 260? or something so they probably corrected this. as for fixing this the car obviously didnt do this brand new off the lot so there has to be a fix....but i cant really think of one...

[knmaynard]

I downloaded from Lexus the "New Features" document for the 1995 SC400 (it was originally used, I'm sure, to educate the sales reps), and guess what it says? Allow me to quote:

"1UZ-FE Engine

On all models, a step motor type EGR valve is used, and the cold start injector has been discontinued."

Ha!

So it's not a first-year car, but it does have a first-year EGR valve! #$%^&*!!!

Good chance its bugs were corrected in '96; this would also explain why so many Lexus service departments are familiar with the--yes, I'll use the phrase--design flaw on the '95.

Thoughts, anyone?

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So does anyone think I can use 96 parts to replace on my 95? I'm still getting the 40mph hesitation. I also got the dreaded redline-without-being-in-gear yesterday on the way home. Our xway moves fast, and I was trying to get into the fast lane and there I sat while my car redlined, in front of fast moving traffic coming up behind me. Kind of *BLEEP*ed off that it does that.

[cal9126]

anyone find any updates or new info on the hestitaion????????

my car seems to only do this the most right after getting on the throttle and driving it hard.......

[KCTalker]

anyone find any updates or new info on the hestitaion????????

my car seems to only do this the most right after getting on the throttle and driving it hard.......

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I recently brought my SC to another mechanic for his opinion (yes, the car still hesitates), and despite my EGR/no-EGR hesitates/doesn't-hesitate demonstration, he thinks the problem is elsewhere--and perhaps the EGR is simply exacerbating the issue.

Anyway, here are some suggestions of his:

1. Get a good, high-pressure fuel-injection cleaning for the car. I plan to do that, because, currently, my SC's hesitation gets worse after a few months, and a bottle of injection cleaner in the tank helps a lot. My guess: it's not helping enough, and a good cleaning may fix the thing forever. I plan to do that fairly soon, and will post here if it helps.

2. He was very wary of the airflow sensor: a little black box attached to the air intake hose, just downstream of the air filter. He tried cleaning it, but that didn't help. His suggestion: If you can find a friend with another SC, ask him/her a favor: swap their sensor for yours and test-drive your car. If that resolves the problem, you know what to do. The up-side: The sensor is held on with something like three screws and an electrical connector; you can remove it in about 30 seconds. The down-side: according to the mechanic, the part goes for about 400-500 bucks! Hence the test.

He also suggested some basic fuel-system issues, such as spark plugs, and fuel filter, but said to try those *after* the previous tests. His contention is that the car is running too lean, and that's why it stumbles.

Remember, all this is about off-idle hesitation. As for the previous poster whose SC redlines without accelerating--that certainly sounds like a transmission issue to me.

[mehullica]

Remove the throttle body and see if any light comes throught the plate. You should have a slight amount of gap between the throttle plate and the body. I'm sure it's got some build-up blocking airflow.