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Discussion Starter #1 (Edited)
Hi,

Have a 2002 IS300 with 202k miles. Past year I've noticed an intermittent drop in power. Sometimes the car is a beast with power and acceleration and other times the thing is gutless and has the following symptoms: stuttering from a dead stop, throttle response lag, NO POWER, and all-around a terrible drive.

Treat the car like a queen, regular oil changes, tune-ups, timing belt change, and recently changed the Throttle Position Sensor (TPS) and calibrated to 0.65 volts (with engine on but not running) and it still hasn't fixed the problem!!

What next? change the Idle Air Control Valve or Accel. Pedal Position Sensor?!?! Might as well change the whole throttle body in that case!!

Also, no vacuum leaks found, PCV valve is new, and no CEL/Codes.

HELP!!!
 

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Checked the MAF?

Its hard to know without CEL's, I assumed you have plugged something in to the port to check for codes even though the cel light is off?
If you are keen you could disconnect the battery to force the ECU to do a full reset, it will usually do a full system check and often throw a code then where it might not before.
 

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Have you tried looking into the throttle body position sensor (attached the spring coil thingy on the back where the cable ties into) inside there are 4 solder joints that tend to crack with heat and time. You can buy the whole unit or strategically make a cut into the white plastic, suck out the old solder, re solder, glue/rtv back together and voila. Happened to me, same symptoms as you describe, I included a pic of what I did and the affected part. The hardest part was removing the sensor PITA to get at those 4 screws.
 

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Have you tried looking into the throttle body position sensor (attached the spring coil thingy on the back where the cable ties into) inside there are 4 solder joints that tend to crack with heat and time. You can buy the whole unit or strategically make a cut into the white plastic, suck out the old solder, re solder, glue/rtv back together and voila. Happened to me, same symptoms as you describe, I included a pic of what I did and the affected part. The hardest part was removing the sensor PITA to get at those 4 screws.
He changed the throttle postion sensor.
 

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Discussion Starter #6
Thanks so much for your help! After much research, and a lot of electrical testing, I believe you're right about the APPS needing to be fixed/replaced. Unfortunately, my soldering skills are weak at best, and I don't want to risk screwing the repair up, having to buy a new part anyways, and also have an inoperable car with Los Angeles parking/tickets being the nightmare that they are.

Think I'm just gonna suck it up and pop for the OEM replacement part :(

Can you tell me if there's any calibration that needs to be done when replacing the APPS (throttle cable adjustment, voltage measuring, etc.)? Or do i just screw that bastard on with the 4 PITA, hard-to-reach, screws, replace throttle cable, plug-in, and cross my fingers?

Thanks for your help,
elliot
 

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No adjustment on the APS side, just the 4 screws.

You can check it as per the screen grab below, but from my experience with faulty throttle sensors they often will often read ok at closed and open throttle, and just at one point will show a fault. So can be difficult to diagnose from the check methods.
 

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Discussion Starter #8
i think the ECU has finally synced with the new TPS sensor i installed because my baby's back!!! Power is killer and my Wilwood 4-Piston front & back brake kits are FINALLY doing what i paid for them to do; braking is strong as hell!!

I disconnected the battery when replacing the TPS (calibrated TPS to .70 VDC) and reconnected battery the next morning. Was super disappointed, expecting everything to be fixed right away, and took a break from wrenching for a few days.

Only drive about 4 miles a day so ECU didn't have a lot of mileage to re-adjust. Power and Braking have been consistent for the past 4 days, and not the on-and-off power/braking loss i've had for a while now.

Fingers crossed but i think i may have finally fixed this annoying fuc**** issue!!

Should i still replace the APPS? Original has about 202k miles/17 years of use, but a new OEM replacement is about $170 from a dealership on eBay.

Thoughts/Suggestions?

Thanks everyone,
elliot
 

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i think the ECU has finally synced with the new TPS sensor i installed because my baby's back!!! Power is killer and my Wilwood 4-Piston front & back brake kits are FINALLY doing what i paid for them to do; braking is strong as hell!!

I disconnected the battery when replacing the TPS (calibrated TPS to .70 VDC) and reconnected battery the next morning. Was super disappointed, expecting everything to be fixed right away, and took a break from wrenching for a few days.

Only drive about 4 miles a day so ECU didn't have a lot of mileage to re-adjust. Power and Braking have been consistent for the past 4 days, and not the on-and-off power/braking loss i've had for a while now.

Fingers crossed but i think i may have finally fixed this annoying fuc**** issue!!

Should i still replace the APPS? Original has about 202k miles/17 years of use, but a new OEM replacement is about $170 from a dealership on eBay.

Thoughts/Suggestions?

Thanks everyone,
elliot
If the sensor is bad, replace it. But it should not have taken so long for the Ecu to pickup the sensors. You still may have an issue. Might be a bad ground issue.
 

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Personally i would wait and see to know if it is 100% again before swapping any more parts out, but its your call in the end ;)

The ECU can take a while to settle down, it sometimes needs to do a couple of full warm cold cycles. When i changed the plugs on mine i reset the system, it knocked like a bastard when it first started and made me second guess everything i had removed and put back on, it settled down a few seconds later but wasn't fully right until i had taken it for a good 20-30 minute drive on the open road. 4 miles a day might not be enough time to let it relearn properly.
 

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Discussion Starter #11
Hey All,

Just wanted to give an update. I can't stand forum threads that just drop-off without a resolution.

Anyways, so-far-so-good with the TPS sensor i replaced and getting my overall engine power and brake power back. Has been about two weeks since replacing TPS and my daily "commute" (2.4 miles) has been consistent with power, acceleration, and braking. Highway performance has also been restored, with no issues getting instant power/acceleration on demand and not the slow accel response and gutless performance i had before.

Hope this issue's resolution (fingers crossed) will help those with similar issues, and I want to thank all who contributed.

Thanks,
elliot
 

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Why hasn't anyone mentioned cleaning/checking the MAF sensor (Mass Air Flow) on the air intake manifold? It's simple, quick, cheap and should be done routinely anyways. A dirty sensor on my '02 triggered the CEL light and three codes pointing to one of the O2 sensors being faulty. Glad I didn't assume it was and replace it.

--TK
 
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