First post so bear with me, I’m still learning the quirks of these cars. I’ve had this LS400 for only about 700 miles and I’m working on getting it to be a reliable daily. Just got done replacing all the bushings and now the electrical has started to give me some issues.

After a cold start the car seemingly runs fine (Only with the AC on) for about 20 minutes. When the AC is off, the throttle hesitates and idle drops low enough to cause the vehicle to shudder but it hasn’t stalled on me yet. More recently, after driving for around 20 minutes, all of the electronics seem to turn off and then come right back on but the motor doesn’t seem to affected. The check engine light has been on, scanned the codes before any of this started happening and got these:P0171

P0130

P0133

P0150

P0153

O2 sensors are fairly new, gas mileage has been fine and I can’t find any vacuum leaks. I tried a different scanner after these issues started to appear and it doesn’t seem to want to connect, which is making me think maybe ecu. I’ve read through the stickied post and plan to replace the capacitors anyways + I’m waiting on a voltmeter to test the alternator because the power steering pump has a slow leak. Is there anything I’m missing? I’m going to try and get the scanner I used the first time to see if it’ll connect at all, but other then that I’m not 100% what could cause some these issues. It’s been a fun learning process for sure.

 

Your above statements reminds me of two issues.

1, The ECU needs to be checked. If not re-capped yet, do it ASAP before copper traces of boards are damaged and melted.
2, The slow leak of the power steering pump should be fixed before the alternator fails. The leaked P/S oil kills the alternator's brushes and slip rings a little by little.

 

ECU caps are on their way and alternator, power steering pump and ps control valve will be a job for next weekend when parts get here. Hopefully it holds out until then as it’s my daily right now. I managed to get ahold of a different scanner last night and it read the codes and live data just fine. Couldn’t tell if everything checked out in the live data because I don’t exactly know what to look for, but there are no new codes. This morning was an especially cold one and on my trip to work the rpm’s dropped significantly every time I took my foot off the gas. When it’s in drive, the rpm’s will catch at around 800-1000 when stopped and then creep down to 2-300 and shudder but not stall. Hoping ecu caps make a difference, and I’m also going to clean the throttle body asap.

 

i agree this sounds like a bad or failing ECU. also low idle is common on these cars for a variety of reasons. for you when was the last time you (or the previous owner) did any transmission work?

i ask because any added strain on the engine, like a unkept trans, will pull the idle down when in gear. case in point when the AC is on, the idle should adjust upward to compensate for the added load. work on the ECU first then see if everything else remedies.

the PS leak is most commonly attributed to an aged o-ring at the very bottom of the fluid reservoir as it enters the PS pump.

 

Great point about the transmission and I’ll definitely keep an eye out, check fluids etc. Previous owner had papers for timing belt and water pump replacement 15kish miles ago and said he had the trans ran through at the same time but that leaves a lot of time for it to cause issues and there no proof. I should have the ECU capacitors in this weekend/early next week and I’ll report back. Thank you for the help

 

I managed to clean the throttle body somewhat and redo a couple of vacuum lines that looked bad this weekend, but the capacitors for the ecu got delayed. Now my car is exhibiting almost all of the symptoms listed in the stickied thread about replacing capacitors. I have to disconnect the battery and reconnect it to get the car to turn on. Parts should be here tomorrow so fingers crossed FedEx doesn’t pull a fast one and delay them again 🤞

 

also check your PCV valve and grommet for cracks around the grommet. I would also do your ECT sensor as that can have a dramatic effect on engine performance and gas mileage.

 

Maybe they're in that massive garbage pile on the tracks where the trains got robbed of all the packages out in Ca.

 

My caps finally arrived and my 220uf got smashed in transit. I had the ECU apart and everything ready before I noticed. Hopefully shipping doesn’t take as long this time. I should have ordered multiple 🤦‍♂️

 

P0171 code and other codes were being thrown from air getting in behind the MAF. The vacuum line that goes to the charcoal canister was shot and the nipple on the s pipe that goes to the throttle body had been repaired before and basically fell off. After fixing, no check engine light after a couple weeks of daily driving.

Got all the parts and the time to fix the ECU last week. Once the caps were replaced it felt like a completely different car lol. Throttle response is a ton better and the transmission shifts like it should. The rpm’s don’t have a mind of their own and I haven’t had any of the electronics act haunted.

Problem is - my idle still seems low but I think I’ve got other issues to fix. Once the car is warmed up, in drive with the AC on, it’s about 5-600 rpm’s and around 300 rpm without AC on. At stoplights I get a lot of vibration through the steering wheel and it occasionally bounces like I’ve got a really lopey cam but the motor is running fine. The car has a lot of miles so I’m probably overdue for motor and tranny mounts. I’m definitely not looking forward to it but I’ve got them ordered and on the way. Still need to fix the PS leak and replace the alternator before it completely goes out but we’ve had a lot of cold weekends recently.

Regardless I’ve had a lot of fun working on this car. It’s already gotten me point A to B more times than the SC300 I used to own (and sold before prices on them skyrocketed &#129394. It’s been a slow morning at work so thanks for coming to my TED Talk.