Greg5OH

the climate control decided to stop aknowledging the interior temp ithink. i set it to 18 and ita still pumping hot air. try to keep jusy the front defeoster on and it gets too hot even eith fan off. Put it to auto, it takes the fan speed to max and im sweating buckets-what the hell! Its worked fine last week!

And then the engine bucking. while crusing or lightly acceleratong it will buck HARD. Can see rpm dip down a few hundred, then resumea normal operation. ita pretty violent feeling. can be on a perfectly smooth road and will still do it. Its random, somwthimea will do it a few times in a few mins, sometimes once an hour.
Could it be a failing tps? im going to use my fathers good multimeter to do the ripple test-see of its the ecu caps

LScowboyLS

Yes, failing ECU capacitors is likely, since engine bucking and climate control issues are two of the most common symptoms.

do you have the special capacitor for the ripple test? - if not, PM me and I will send you one at no charge.

you could also pull the computer out and open it up, sometimes capacitor leakage is obvious, but many times it is hidden, because the leakage starts on the underside of the capacitors. However this is worth doing, because the ECU can have other obvious issues beside just leaking caps, I have seen burnt power transistors and burnt high wattage resistors as well, and both were obvious to a trained eye such as myself or Yamae, so take some very clear pics of the inside of the ECU and post them to my capacitor thread

Have you scanned this car for diagnostic codes?

Largefarva

I'd start with a scan as stated, I doubt it would be a TPS, likely a plug or coil breaking down, if its not a computer issue. Cowboy, where is the ECM located on these?

LScowboyLS

Yes, this bucking could also be a coil or even an alternator or battery going bad or bad battery connections, so I would first check the voltage across the battery with car off, car running at idle with headlights on, and car running at ~1700 rpm with headlights on and post those voltages here.

Where the ECU is located depends on which year of Lexus and which model. - Some models, like the GS have their ECU's under the hood near the battery, while the LS400's ECU is inside the car behind lower glovebox. You can use part diagrams from Sewell or other online dealership to help locate the ECU if you do not own the factory service manual.

Greg5OH

Battery is new, voltage is 13.2 idle 13.9 at 1500.
I do not have the cap. lscowboy id appreciate that very much! Im going to check codes tonorrow. car has 115k miles.

LScowboyLS

PM me your address for cap

Greg5OH

no codes found. I also doubt that its ignition coils, doubt all 8 of them would stop working at the same time like that. Car bucked twice on my way to work this morning, like a 3/4 second loss of power, rpms dipped 200 revs.

Funny it didnt do it at all on my 4 hour trip on monday, but did it about 10 times on the friday.

cobalt91

What RPM range does this usually happen in?

Greg5OH

1500-2500, crusing range,

MattLS400

Interesting....This is the same exact problem that I am experiencing with my 1996 Celsior- UCF21 with 1-UZ-FE,



Greg, I must ask you..The dip of the RPM down to a few hundred then resumes--does this happen irregardless of whether or not the engine is heated or cold . Meaning, does it happen all the time, like even from first start ?

Your response can be very beneficial to you, as it would avoid having to spend alot of $ by changing unnecessary parts. To start with, as the Cowboy advised, having a look at the ECU Caps is a good idea.

See post# 1...Your symptoms are very close to mine...

https://www.clublexus.com/forums/ls4...ml#post8091066

* No codes
*engine buck then dip of the idle when lightly accelerating ---at half temp---
*Engine would only buck when you are lightly accelerating, but otherwise on full acceleration no engine buck




*I bet your 4 hour trip was on the freeway...why ? because thats full acceleration, therefore there is no engine buck
*When it did buck 10 times on Friday, thats because you were lightly accelerating, 1300 -1900 RPM in moderate traffic...Not so?

LScowboyLS

Matt - I think you have two issues in play

1. I am still not convinced that you have the correct capacitors installed in your ECU

2. you have an overheating problem that is still to be determined, which could be several things, such as:

● bad radiator
● bad fan clutch
● overcharged A/C system (if overheating is only when A/C is on)
● blown head gasket
● air in cooling system
● defective water pump
● incorrect coolant/water ratio
● stuck closed thermostat
● jumped time or incorrectly installed ignition cap or rotor
● crank pulley has slipped resulting in incorrect valve/ignition timing (two cases of this discovered on Club Lexus in the last month)

Greg5OH

Mine is irregardless of cold, hot, accelerating or crusing. 100% totally random. coild be accelerating heacy, lightly, cruise control on at 70, then THUNK. pulling the ecu real soon