jonnydclark

After posting in ClubLexus.com forums and getting nothing but crickets I'm asking for my fellow yota's advice.

99 GS300, soon after fuel pump change started exhibiting this behavior.

Consistently (with small variations) runs extremely lean between 2500 rpm and 3200 rpm. The HP and torque drop and the RPM climbs very slowly. After 3200 plus or minus it hits strong like a 2 stroke hitting power band.

It does NOT miss fire, rough idle or show any indication of anything but being lean. Trouble codes are either none or sometimes it shows P0171 bank one lean.

I cleaned the MAF sensor with MAF cleaner (about 20 times by now). I tried a new MAF sensor in it. No help.

I had the fuel pressure checked and it was fine. The foreign car repair shop told me I needed new upstream O2 sensors. I told them that was a symptom, not a cause of it running lean, declined to have them do it for $500 and then replaced them both myself off Amazon with Denso made to fit for $100.

No change.

After resetting the ECU by disconnecting the battery it ran like crap. Idled at 300 rpm, almost died when I gave it gas in park. Let it adjust itself and figure out its MAP a little (never used to have to do that after disconnecting the battery but it has been pretty consistent since this problem started). Drove it down the road and it cleaned up a little (was running like a dog when I first left the driveway, not really missing but obviously terrible fuel to air ratios and response). Then within about a 10 minute drive it was running ok except for the 2500-3200 rpm

Anybody ever heard of the VVT acting up? It either isn't giving it enough gas or it is really retarding the timing. I would really like to sell the car but don't wan to give it away in this condition.

Should I take it to the stealership?

Kiroshu

The VVT on multiple early model toyota engines have a long history of causing single bank misfires not normally associated with a lean condition....

Worn and or improperly adjusted spark plugs...?

Timing belt worn and or out of adjustment...?

Faulty fuel pump...?

Incorrect fuel pressure...?

Exhaust leaks...?

Intake air leaks(vacuum)...?

jonnydclark

Thanks.

It doesn't misfire. I'm leaning to faulty fuel pump or bad computer. The relearn after disconnecting the battery is more concerning and causes me to fear it is the computer.

I'm going to try to check the fuel pump volume but not sure why it would run at higher rpms better than mid.

m44offroad

Clean your throttle body with a rag and throttlebody cleaner and see if it helps with relearn. Carbon caked up on the throttle plate will cause the low idle when reconnecting the battery. Other than that its hard to help without seeing livedata

Kiroshu

^-- X2 on that as well ^_^

cheftank

lexus is known for the ecu having leaking capacitors (spelling). I would also remove and clean the IACV off the intake manifold. While you aren't having idle issues, it could only show problems in open loop.

experience: 1994 sc300 with a 1jzgte single turbo

www.driftmotion.com can diagnose any ECU issues and repair them, and aaron is good people.

hope this helps

Nebo

Last time I had a similar issue it was my fuel pump believe it or not. Pull it out and inspect it, make sure you dont have bad gas.

oldblue

all of this happened after a fuel pump replacement huh. now, why was the fuel pump replaced? you say its running lean, why do you think this or what data is telling you this? do you have a scanner capable of reading live data? we'll got this ˟˟˟˟ figured out, dont sweat

jonnydclark

So I finally followed my gut and replaced the new Advance Auto fuel pump with a used OEM one (sending unit and all) off of Ebay. Immediately worked like a charm and have driven it about 5000 miles without issues.

Original one was replaced after it was suspect due to running out of gas on freeway after driving for 4 hours straight. Gauge showed 1/4 tank but in retrospect the pump was fine, only the connecting line between the two halves (horshoe over the drive shaft) of the gas tank. It has 2 sending units and the side without a pump was staying half full and the gauge would average the level between them i guess. Not a problem if you went around a corner occasionally and re-leveled the sides but filling up and driving straight for that long meant one side drained but not the other due to a blockage.

Anyway, glad I figured it out instead of selling the car.