jwotis

Hey guys, I'm new to the forum, but I've been wearing out the search box for the last couple weeks. I recently purchased an A/T 93 ES300 with about 177K miles. Bought to replace my beloved (but falling apart) 88 5spd Celica, as we needed something that the wife could/would drive as well. First lexus vehicle. Had a mechanic look it over before purchase, and other than routine maintenance issues (brakes and tires in the rear, some lightbulbs) all he identified was motor mounts (front and dogbone) and a small leak in the valve cover gasket. I had a mechanic replace the mounts and put in a starter myself after the existing one started failing almost immediately (~2 days after driving it away. Around the same time a crack developed in the sunroof and spread halfway across the glass in a single day/night... at least that was a reasonably cheap fix with a salvage part and some wrench work).

Current problem: CEL came on two nights ago, pulled code 25 (air fuel ratio fault, running lean). Refueled for the first time last night and checked mileage - seems quite low (12 mpg) even accounting for cold weather (I'm in PA), city driving, and more idling than normal due to repairs and checking things. Have noticed some fuel odors in exhaust during warm up. The car idles low at start-up, at least since the starter replacment (didn't notice anything abnormal before, but I didn't specifically check rpms either). I understand that a low idle may be normal immediately after an ECU reset, but it's been driven around a bit and is still at 500 - 700 rpms, which is especially low considering the cold weather. In order to get it to start this morning (coldest start since I've owned it) I had to give it gas for the first 30 seconds or so to keep it from stalling out. Once the engine warmed up, it idled fine (at 500-700 rpms). Have had some intermittent rough idle issues (steering wheel shake) and a slight shudder/shimmy, only during acceleration, at low highway speeds. Hoping new rear tires help the latter.

So.... any advice or recommendations for a course of action based on the above? I'm a reasonably handy guy but the most complicated automotive jobs I've done so far were the starter on this car, brake pads/rotors, and a high-pressure power steering hose replacement on my Celica. Don't know much about engines except what I've picked up reading forum posts. From the research I've done, I've leaning towards the following potential issues:

1) dirty IACV - have some carb cleaner and will be cleaning soon; need to locate, but bookmarked a thread on here that looks good. This was on the to-do list before the CEL light, just as good maintenance. Unsure if it could be responsible for all issues above, but seems like it might be a contributor.
2) Vacuum hose leak - It's an old car and the hoses look original. People make it sound easy to test and replace but I'm not confident how to identify a "vacuum hose" and am worried about damaging belts or creating a fire hazard if I start spraying brake cleaner around *****-nilly. Very little engine experience.
3) Oxygen sensor - Looks relatively straightforward to replace the upstream sensors, and they seem to be a main cause for CEL codes 25/26. Should upstream and downstream sensors be replaced at the same time? Does it matter?
4) Coolant temperature sensor - possibly related to the cold weather stalling?

I've got time today and tomorrow to troubleshoot, then I'm out of town for at least week, and would like to leave a functioning car for the wife so she can get around. Is it safe to do some light driving given the above symptoms, if I can't get it fixed before I leave?

Thanks for any help!

UPDATE:

Tentatively, the idle issue is solved-- either I stared at the engine very persuasively (unlikely?), or the bottle of fuel injector cleaner I put in with the last/first fill-up circulated enough with the drive this morning to straighten things out a bit. When I started it up this afternoon, the idle rpms shot right up to ~1500 initially, then settled down to ~750 after it warmed up. This seems in line with what I've seen others report. I ran several errands over a few hours and it continued to behave well. Next up is to replace the PVC valve, which is cheap, seems easy, and might give me an idea of what to expect on other components in terms of grime/buildup. Still plan to clean the IACV/Assy - but I think I'll wait until the weather improves a bit.

I'm going to recheck and then clear the CEL code. It seems to my uneducated mind that dirty/clogged fuel injectors might lead to an "engine running lean" code, so hopefully that's all it was.

For any experienced Lexus owners out there still reading, I'd really value any advice for priority maintenance items or parts you would check on an ES300 of this advanced age, especially given the issues I've had so far.

Edit 2: Welp. The PCV valve was *very* easy - it must have removed itself when I was driving around earlier and was sitting next to the hole on top of the cam cover. I did give it a slight tweak earlier when looking at the part but didn't think I had even budged it, so not sure why it popped off. The old part was dirty, but did not appear at all clogged - probably didn't need to be replaced. The rubber gasket it sits in was slightly torn but still looked like it could make a seal, so I cleaned the gasket a bit and popped the replacement back in place.

gem9209

I had a similar problem and took it to the smog repair shop
they fixed my timing and decarbonized my engine seemed to help all around.
also check all vacuum hoses and o2 sensors
(my car threw 2 codes because of an unconnected o2 when I first got it)

jwotis

decarbonized is basically cleaning the engine interior, DIY with seafoam or similar?

The previous 'fix' didn't last long - my wife tried to use the car while I was out of town and it stalled out immediately on start.

I cleaned the throttle body today - read a service bulletin somewhere that a dirty throttle body was a known cause for the low idle/stall, particularly after an ECU reset. This seemed to align with the problem popping up after I replaced the starter. The throttle body/plate was very dirty, and there was oil/gunk dripping out of the interior air intake hose when I took it off. Not a clean engine.

It seems like it could use an engine cleaning treatment, but I'm a bit nervous about running Seafoam (or similar) through the engine given the amount of gunk that was in there. I assume an oil/filter change would remove most of it, but I'm gonna have to read and reread the thousands of seafoam threads before I'm going to feel comfortable tackling that. Trying to DIY as much as possible.