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Sudden drop in RPM's? and some other issues....

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Old 07-10-14, 05:39 PM   #1
RugbyDad
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Default Sudden drop in RPM's? and some other issues....

Let me preface this with all the work I have had done on my 2000 ls400.

ECT sensor replaced
PCV and grommet replaced
throttle body cleaned while still attached to motor
MAF sensor cleaned
Air filter replaced
Seafoam treatment through brake booster vacuum hose
Battery replaced
I ordered ECU caps but haven't found a place to do the install.

Ok, here goes with me trying to explain this thing.

Problem 1 - When driving along at any speed in any gear no matter if the car is warm or cold, when I let off the gas, the rpms immediately drop from wherever they are to around 650-1000. They pick back up when I put my foot back on the gas with a noticeable hesitation. It's like a manual transmission. When you step on the clutch pedal, the car is for all intents and purposes in neutral and the rpms drop to normal operating speeds. But the ucf20 has an automatic trans. I'm confused about this. I read something about a locking torque convertor and maybe that this is just normal but It bugs me because out of all the cars I have ever driven, I have never experienced such a thing.

Problem 2 - Car jerks when selecting a gear. From Park to Drive, or Drive to Reverse, or anything to anything, the car jerks. No noise like a thunk or thud. Just the car jerks. I have tried putting the parking brake on whenever I move the gear selector but I can still sort of feel the car jerk. I ordered a tranny mount, hopefully that corrects it but if that isn't the case, I will be sure to ask about it. I checked the trans fluid and it doesn't smell burnt and as far as I can tell is reddish in color and at an ok level. Maybe I should do a drain and fill?

Problem 3 - The car hesitates or at least to me seems to hesitate. It isn't an immediate response when I step on the gas. Bothersome to say the least. I also get pretty horrible gas mileage. According to the onboard computer, I'm sitting at around 16mpg for combined city and highway driving (tank AVG).

Problem 4 - While braking quickly, not really all that hard, when the car gets to about 20mph, the car lurches forward a bit, like it just downshifted abruptly. Maybe lurches isn't the right word. It just feels like the car pushes forward a bit like someone tapped my bumper softly.

Problem 5 - Steering wheel shakes above 40 or 50 mph. Very slight shake. Can't really see it but can definitely feel it. I recently brake(d?) quickly from around 70/80mph to a stop and could feel a shake in the brake pedal. The dealer says he replaced the brakes because when I first test drove the car the shaking was much worse. Replacing the brakes as the dealer says he did definitely calmed the shaking down as far as the braking shake goes. The steering wheel shake has always been there.

I'm thinking problem 1-4 is trans related and want my wife to run like new. I plan on getting the ECU caps replaced in the future, not the near future just sometime later this year. Maybe before winter. I also want to clean the IACV but can't for the life of me find where it is. After google searches and CL searches I can't find the IACV for the 98-00 ucf20. Pictures? I thought I read somewhere on CL that the 2000 doesn't have an IACV. I think Yamae said it.

Oh on another note, the throttle cable seems a little loose. I mean there is some play in it without the throttle assembly moving at all. Maybe thats the solution to my response issue, although I don't want to mess with it because my idle speeds are well within range. About 1000-1200 when the ENGINE is cold (note I said engine, doesn't matter what the temp is outside), and anywhere from 550/600-725 when warm.

Sorry for the long post.
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Old 07-10-14, 06:26 PM   #2
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Correct. The 2000 does not have the IACV and normally do not have ECU cap problems(more common with 97 and earlier models). Do you have a check engine light on?
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Old 07-11-14, 01:42 AM   #3
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No CEL. When I drove to work this morning, I noticed the vibration is also present in the seat. Not just the steering wheel. Never noticed it before.

update: now i can feel the vibration in the seat, see it in the steering wheel and I felt the vibration when braking around 20 mph again. I have no clue where to even start as far as the vibration goes.

Last edited by RugbyDad; 07-11-14 at 12:32 PM..
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Old 07-11-14, 06:40 AM   #4
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Quote:
Originally Posted by RugbyDad View Post
I'm thinking problem 1-4 is trans related and want my wife to run like new. I plan on getting the ECU caps replaced in the future, not the near future just sometime later this year. Maybe before winter. I also want to clean the IACV but can't for the life of me find where it is. After google searches and CL searches I can't find the IACV for the 98-00 ucf20. Pictures? I thought I read somewhere on CL that the 2000 doesn't have an IACV. I think Yamae said it.
Sounds like an AT issue to me too, but you haven't done any of the AT related affairs yet according to your report.

Try doing an AT/Engine stall test as a first step. It should be worked at 2250150rpm.
This is a bit dangerous to do for a home mechanic though. You need to rock up the rear wheels in addition to use the side brake and the foot brake as well. You also finish it within 5 seconds.

Due to the power supply and the load differences from earlier models, 98-00 models's capacitors last longer. But Toyota has been kept using the infamous capacitors that contain quaternary ammonium salt and those capacitors still fail when used for a long time. You'd better check the ripple first. As long as I have experienced, the first problem was the AT shift problems. Next comes the increased resistance issue of a resistor used in the power supply circuit.

Regarding the IACV, as Doc Yota mentioned, there is none for a 98-00. The main throttle plate and the body pass through the air for the entire RPM range with the mixing air to injectors.
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Old 07-11-14, 03:16 PM   #5
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@Yamae. After doing a couple google searches, I would definitely NOT want to do that myself. The point of the stall test is to rule out the torque converter as the culprit right?

I'm going to take her to a trans shop and have them run some tests. Check my trans mount, maybe drop the oil pan and check the solenoids or something. Maybe do a drain and fill and quite possibly do the stall test. Although I'm a bit hesitant about the stall test.
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Old 07-11-14, 03:16 PM
 
 
 
 
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