Sc 400 Hesitation...?

[KCTalker]

Hello, all, from a brand-newbie!

I just bought a '95 SC 400 (87K, nice and clean), and since I'm brand-new to the car, I've got a question I think you veterans could easily answer.

Bear in mind, I'd been driving a five-speed, four-cylinder car for 15 years up to this point, so I honestly can't tell if it's the car, or if it's me. Here goes:

At low speeds (5 mph) and low revs (1,500 rpm), when I give the car very light pressure on the accelerator, it seems to hesitate.

However: the thing idles like a champ, races to redline easily and smoothly, and gives flawless performance under every *other* set of circumstances. Am I, perhaps, simply not giving the car enough gas for the automatic transmission to really "bite" into the gearing sequence it wants? My wife's got a '95 Celica automatic, and I don't notice this phenomenon when I drive it.

Two more bits of background about the car: 1) When I first brought it home, it stalled twice, despite otherwise-perfect performance. I brought it back to the dealer, who found, and replaced, a clogged gas filter. No stalling since. 2) Today, I dumped a bottle of fuel injector cleaner into the tank (I'm suspecting the previous owner may have skimped on gasoline, or simply never drove the car very hard). The cleaner, combined with a nice, high-revving cruise for about an hour, seems to have helped the car, overall, enough to notice. I still can detect the hesitation I described above, but it's pretty faint--just present enough to notice.

I put a quick 100 miles on the thing with the injector-cleaner so far; think the performance will continue to improve? Has anyone else noticed this "hesitation" I've described? Or am I just way too nit-picky?

Anyway, thanks, all, for taking the time to read this (way-too-long) message; I'd appreciate your thoughts!

[jzz30]

does it seem like the tranny is down shifting? and with 87k miles on it its time to do some GM(general maintenance) if it hasnt already been done. timing belt water pump,plugs, plugs wires, rotors, caps etc... you can check the trans fluid to see if its dirty or there for that matter.

[Theodore]

i had the same problem. i reset the ecu, and i did notice alittle bit better difference. try that as well.

[KCTalker]

Hi, and thanks for the replies!

First, what's the "ecu"?? For that matter, how do you reset it?? It sounds simple; Theodore says it helps; and I'd certainly love to try it.

As per jzz30's questions, the tranny seems to shift fine; its fluid is clean with no burnt odor, etc. Spark plugs are new. Spark plug wires were just checked by a mechanic and deemed "fine" (but not replaced).

Also, as per the timing belt, the owner's manual doesn't say when to replace it--unless you're driving your SC like a taxi! In my experience with other cars, 80K is about time to do it, so at 78K, it's pretty near due.

Any other thoughts? Thanks again for the prompt replies!

[Dere2000]

I have a 95 sc4 and I have the same problem. I think I need to replace the plugs and the fuel filter to fix the problem so I am going to try that.

[jzz30]

to reset the ecu you can just disconnect the battery and wait a minuite or two before connecting again. as for timing belt its almost time and if you are doing it then change the waterpump while your at it because you need to take it off to do it anyway. try check your throttle position sensors for proper resistance.

[Skydiver]

I have the same car (95SC400) and the same problem. Were you successful in correcting the hesitation issue? How?

[KCTalker]

I have the same car (95SC400) and the same problem.  Were you successful in correcting the hesitation issue?  How?

←

Hey, Skydiver,

Problem is still there. Have since replaced timing belt, water pump, drive belt, power-flushed the tranny, replaced the idle-speed control valve (which turned out to be the true source of the stalling), and while all that stuff is certainly good for the car overall, I still have the hesitation issue.

A bottle of fuel injector cleaner seems to help--but the help only lasts for about 3/4 of a tank!! Insane. I brought it back to my local Lexus dealer a zillion times, but they tell me the car is fine. I disagree: I drove two other SC400's right before buying mine, and didn't experience the issue on the others.

Coincidentally (considering you're replying to a post I logged this summer), I'm about to try my luck with another Lexus dealership, a little further away, and may have some info/updates sometime next week.

Meantime, if you happen upon any other info, please post it!

[knmaynard]

Mine does the same thing. Usually if I'm barely on the throttle around 40mph is where I notice it hesitating, like a haltering. If I push down it goes away, if I let off completely, it goes away.

[BMAN1113]

This almost sounds as if one of your O2 sensors may be getting lazy (fixing to go bad). A symptom of this would be what's referred to as "bucking". This is more noticeable at lower speeds and crusing at 55mph on the freeway. In full throttle it will feel smooth. When they get lazy they arent bad enough yet to necessarily trip the "check engine" light. It does seem kind of early for one of these to be going bad, but it happens. I started noticing this on my '93 at around 105k (132k now). I dont really worry about it. When it gets warmed up it feels better. If you are wanting to take care of this, the SC400 has four O2's. They run about $180.00 each on the net. I've decided to replace all four when the "check engine" light appears. So till then, I'm just driving.

[SCdriver]

I don't know if this will help or not but:

1) Put in 2 reg bottles of techron or one large bottle (20oz) of techron with premium fuel and it should clean the intake system ,valves and injectors. Run the car until the tank is almost empty and then put in the techron and then the fuel and don't dilute it by filling up before go through most of the tank.

2)Change your spark plugs to NGK iridiums

3) Change your spark plug wires

The techron is available in most auto part stores (Don't use a cheap brand get techron) The iridium IX NGK plugs are available on Ebay for around $48 just make sure they are gapped properly before they are installed. The new spark plug wires can be purchased at the-best -source.com ... I use them to buy nippon oil filters and oil drain plug gaskets etc. and save around $12 from what lexus charges for them. Good Luck

[Skydiver]

Appreciate all the quick replies, advice and experiences. Yeah, I'm just starting my journey with this car. What's wierd is that the hesitation doesn't seem to be as noticable when the engine is cold. At start up, and for the first 5-10 minutes, my 95SC400 idles at about 1100r's and seems to ramp up smoothly off the line. Then when it warms up, it becomes jumpy between normal idle speed (500-600) and about 1300 ('bucking' is also a good descriptor) . But if I punch it hard, it takes off. So I doubt it's tune up material, although I'll do that anyway just to establish a baseline--swap the plugs and wires as suggested. My local dealer mentioned something about this issue and how it might be related to the throttle body. The dealer also suggested reseting the ecu, but that it would likely not solve the problem - only establish custom shift points for the tranny as it 'learns' the way I drive. Hey Bman1113, are there 'throttle body sensors' on this V8? Are they the oxygen sensors you refered to? Thanks.

[geneauf]

Appreciate all the quick replies, advice and experiences.  Yeah, I'm just starting my journey with this car.  What's wierd is that the hesitation doesn't seem to be as noticable when the engine is cold.  At start up, and for the first 5-10 minutes, my 95SC400 idles at about 1100r's and seems to ramp up smoothly off the line.  Then when it warms up, it becomes jumpy between normal idle speed (500-600) and about 1300 ('bucking' is also a good descriptor) .  But if I punch it hard, it takes off.  So I doubt it's tune up material, although I'll do that anyway just to establish a baseline--swap the plugs and wires as suggested.  My local dealer mentioned something about this issue and how it might be related to the throttle body.  The dealer also suggested reseting the ecu, but that it would likely not solve the problem - only establish custom shift points for the tranny as it 'learns' the way I drive.  Hey Bman1113, are there 'throttle body sensors' on this V8?  Are they the oxygen sensors you refered to?  Thanks.

←

[geneauf]

Hello, all, from a brand-newbie!

I just bought a '95 SC 400 (87K, nice and clean), and since I'm brand-new to the car, I've got a question I think you veterans could easily answer.

Bear in mind, I'd been driving a five-speed, four-cylinder car for 15 years up to this point, so I honestly can't tell if it's the car, or if it's me. Here goes:

At low speeds (5 mph) and low revs (1,500 rpm), when I give the car very light pressure on the accelerator, it seems to hesitate.

However: the thing idles like a champ, races to redline easily and smoothly, and gives flawless performance under every *other* set of circumstances. Am I, perhaps, simply not giving the car enough gas for the automatic transmission to really "bite" into the gearing sequence it wants? My wife's got a '95 Celica automatic, and I don't notice this phenomenon when I drive it.

Two more bits of background about the car: 1) When I first brought it home, it stalled twice, despite otherwise-perfect performance. I brought it back to the dealer, who found, and replaced, a clogged gas filter. No stalling since. 2) Today, I dumped a bottle of fuel injector cleaner into the tank (I'm suspecting the previous owner may have skimped on gasoline, or simply never drove the car very hard). The cleaner, combined with a nice, high-revving cruise for about an hour, seems to have helped the car, overall, enough to notice. I still can detect the hesitation I described above, but it's pretty faint--just present enough to notice.

I put a quick 100 miles on the thing with the injector-cleaner so far; think the performance will continue to improve? Has anyone else noticed this "hesitation" I've described? Or am I just way too nit-picky?

Anyway, thanks, all, for taking the time to read this (way-too-long) message; I'd appreciate your thoughts!

←

[geneauf]

Hello, all, from a brand-newbie!

I just bought a '95 SC 400 (87K, nice and clean), and since I'm brand-new to the car, I've got a question I think you veterans could easily answer.

Bear in mind, I'd been driving a five-speed, four-cylinder car for 15 years up to this point, so I honestly can't tell if it's the car, or if it's me. Here goes:

At low speeds (5 mph) and low revs (1,500 rpm), when I give the car very light pressure on the accelerator, it seems to hesitate.

However: the thing idles like a champ, races to redline easily and smoothly, and gives flawless performance under every *other* set of circumstances. Am I, perhaps, simply not giving the car enough gas for the automatic transmission to really "bite" into the gearing sequence it wants? My wife's got a '95 Celica automatic, and I don't notice this phenomenon when I drive it.

Two more bits of background about the car: 1) When I first brought it home, it stalled twice, despite otherwise-perfect performance. I brought it back to the dealer, who found, and replaced, a clogged gas filter. No stalling since. 2) Today, I dumped a bottle of fuel injector cleaner into the tank (I'm suspecting the previous owner may have skimped on gasoline, or simply never drove the car very hard). The cleaner, combined with a nice, high-revving cruise for about an hour, seems to have helped the car, overall, enough to notice. I still can detect the hesitation I described above, but it's pretty faint--just present enough to notice.

I put a quick 100 miles on the thing with the injector-cleaner so far; think the performance will continue to improve? Has anyone else noticed this "hesitation" I've described? Or am I just way too nit-picky?

Anyway, thanks, all, for taking the time to read this (way-too-long) message; I'd appreciate your thoughts!

←

←

[BMAN1113]

I'm sure there's a sensor for almost everything in this car. Sometimes I lift the hood and become almost frightened by the complicated array of sensors and other electronics. It just seems like it would create such a large margin for error. Amazed that I've had hardly any problems to speak of in four years of ownership... and I drive my car hard. The O2 (oxygen sensors) that I referred to are located in the exhaust system. Each exhaust pipe has one in front of the catalytic converter and one behind (4 total). I've heard from several people that the O2's behind the catalytics never go bad, so you may just want to try the two fronts first. Fortunately, I haven't heard of too many problems with sensors located in the engine compartment area. O2's located in the front section of the exhaust, constantly contend with extreme heat that ends up taking a toll over time. You also mentioned that you don't experience any problems when cold. I think the temperature at the O2 sensor has to reach above 330*C for it to kick-in and start controling the fuel mix. Sounds exactly like your deal.

[92Lex]

I've heard from several people that the O2's behind the catalytics never go bad.

←

I wouldn't say downstream O2S never go bad.

[Skydiver]

I'll have the o2 sensors looked at and report back asap. Thanks.

[KCTalker]

Hey--

Thanks for the Techron tip; I'll try it.

Just did a search on this board for the word "hesitation", and wow, are there a lot of posts!

Anyway, here's my latest dealership experience, which I think the readers here will find interesting:

After my local Lexus dealer insisted there was nothing wrong with my car ('95 SC4, 83K), I tried another Lexus dealer nearby. As soon as I described the problem to the service manager, he said, "A '95? Oh yeah: EGR gasket modification!"

Huh? I hadn't seen this on *any* posts here; it certainly seemed intriguing.

Still, I insisted on demonstrating the issue to a technician in a road test, so their top diagnostic guy hopped in the car with me. Soon as he gave it gas off the line, it stumbled. Then he said, "Let me see something," and pulled over to the side of the road.

He then popped the hood, and yanked out an electrical connector from the engine. "What's that?" I asked, and he replied, "EGR."

We got back in the car, which was glowing a "Check Engine" light--and the problem was gone!

According to the tech, it's a problem with this car, stemming basically from the way the ECU is programmed. He said the EGR system is supposed to open up at highway speeds to burn off un-burned exhaust gases, but sometimes, the valve opens up when you first accelerate, and this, he said, is the cause of the problem.

And he said he knew of a fix, or more realisitcally, a work-around: He offered to modify the car, by installing a washer in the EGR valve gasket to effectively reduce the size of the orifice. He said that he could only reduce it so much, because if he did it too much, it would trigger a "check engine" light which, here in California, means your car fails its smog-check and is thus illegal to drive. (Not to mention the fact that a continuously-glowing "Check Engine" would mask any *real* problems that arise.)

So. I okayed the 95 bucks for an hour of shop time for him to make this alteration. And I just got the car back. I was told that the car would be better, but not perfect.

I'm not too sure I agree. It still hesitates, perhaps a little less than before, but I think I've had better luck with fuel injector cleaner! (And now look forward to trying a big bottle of Techron.)

The technician also confirmed what everyone here's been saying about the ECU, although he added that it's best to disconnect the battery for about *ten* minutes to truly blank it out. He said it would then "forget" its last 1,000 miles of driving patterns, and re-learn them from scratch. He also advised driving it hard, in "power" tranny mode, during this learning phase.

Okay. So, if any of you are still with me after this War-And-Peace-length post, I'd be curious to others' reactions. Anyone else wanna try disconnecting the EGR valve and seeing what happens? Please note that mine is a California car, not 49-states, so I don't know if that'll be a factor.

Anyway, just thought I'd share my experience, since this is *clearly* a designed-in problem that's endemic to these cars.

[92Lex]

EGR= Exhaust Gas Recirculation...it re-circulates some of the unused exhaust gases back into the combustion process. The EGR valve is normally closed only at idle and wide open throttle. If you disconnect the vacuum line to the EGR while at idle it shouldn't do anything to the vehicle...if you apply vacuum to the valve at idle the engine will stall...that's a working EGR valve.

I'm a smog tech...what were your test results?

[KCTalker]

EGR= Exhaust Gas Recirculation...it re-circulates some of the unused exhaust gases back into the combustion process. The EGR valve is normally closed only at idle and wide open throttle. If you disconnect the vacuum line to the EGR while at idle it shouldn't do anything to the vehicle...if you apply vacuum to the valve at idle the engine will stall...that's a working EGR valve.

I'm a smog tech...what were your test results?

←

Thanks for the info. When you say "test results," do you mean smog-test? I know it passed when I bought the car in June. Or do you mean performing the test you described above? Anyway, the Lexus tech didn't touch any vacuum hoses in my presence, just the electrical connector to the EGR valve.

I plan to replicate his little test (yanking the electrical connector) on my own, to see if it indeed makes the hesitation issue go away. (Because he, not I, drove the car after he had pulled the connector.) That's the first issue. Because if pulling the connector truly eradicates the problem, I'll know that the tech's diagnosis was correct, even if his solution wasn't. And if it *doesn't* do anything, then I'll know that the diagnosis (e.g., EGR) was wrong, and I need to resume my trouble-shooting elsewhere.

[KCTalker]

Hey 92Lex (and all SCers, for that matter),

Just ran my little test, in which I duplicated what the Lexus technician had tried. That is, I disconnected the elecrtical connector from the EGR valve atop the engine, and drove it around awhile with the "Check Engine" light glowing, just to see what would happen.

Sure enough, the low-revs hesitation is *gone*! And what the technician told me (namely, that the thing is the culprit) is true.

I've also had the chance to drive a little more with his work-around fix (the reduced EGR orifice [created via a washer]), and do notice that the car is improved, by I'd say 50-60 percent. It still stumbles now and then, but is noticeably better overall. So, really, everything this technician told me has panned out.

Which of course, raises some questions: Would it damage the car to drive it with the EGR electrical connector disconnected indefinitely? Naturally, this would cause the ECU to log codes from the "Check Engine," but who cares? Could it possibly cause some long-term buildup that might hurt the car's chances of passing a smog-check, after re-attaching the connector?

And finally, if the real culprit here is the ECU, which is sending these crappy commands to the EGR in the first place, what's the real solution? I've noticed--from this board, at least--that owners of '93 through '95 SC400s gripe about this problem, but I see no problems with the later-model cars. Was the ECU revised in later years?

If so, could a '95 be retrofitted with an (admittedly expensive) later-model ECU? Could the existing ECU somehow be re-mapped? I'm more curious than anything, given the contraints of my ECU-remapping skills, not to mention my budget!

P.S.--I could snap a quick digi-pic of the connector in question, in case any other newbies out there (like me) need help recognizing it under the hood. Just post and ask.

[knmaynard]

P.S.--I could snap a quick digi-pic of the connector in question, in case any other newbies out there (like me) need help recognizing it under the hood. Just post and ask.

←

I'd like to see a pic, if you have a chance.

[BMAN1113]

I'd like a pic also. I thought for sure this problem was O2 related. I'll have to try it.

[BMAN1113]

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?