TRP00

I having a hesitation problem on my 2000 TL. After starting the car it idles fine but when I go to accelerate it will stumble. If I press the accelerator past half way it will jerk and accelerate hard. If when it stumbles I let off the accelerator it will go back to idle. If when it stumbles I continue to hold the accelerator in the same place it will continue to stumble until almost stall. It only does this after starting. Once it get past this it will run and accelerate perfectly until you turn the car off and let it set for over 15 minutes. It has no CEL or codes. Things I have replaced all 6 coils, spark plugs, TPS, MAP sensor, battery and air filter. I have also cleaned EGR ports, TB and ran fuel injection cleaner through it. If anyone can help me diagnosis this problem I would greatly appreciate it.

Saudade

Do you have a code reader that can read/record live data?

TRP00

Yes I can read live data and I think I can record live data. I never have recorded data before but I believe I can figure it out.

Jon M

Since you have installed coil packs etc. lets assume you have spark, unless you left a rag or have a critter in you air ducting or throttle body or the throttle is completely closed you should have air. Since it runs fine after it warms up lets assume the timing is good. I would lean toward assuming fuel is the issue. If you can check the fuel pressure after the car has cooled down it might narrow it down. If it was me I would be thinking fuel pressure regulator, fuel pump type of issue. I would put a gauge on the fuel pressure regulator and monitor when it starts and then when you hit the accelerator, the pressure shouldn't vary much at all. There is an older thread where I had a very strange fuel issue and it has the fuel pressure specification in it.
https://acurazine.com/forums/2g-tl-p...-ideas-991328/

beatsme

I almost never post here. But have you tried using different gas? Specifically a different gas station?

About a year ago my 2003 TL started bottoming out on me in varying conditions and situations (in town and on the interstate). I had recently changed jobs and was also stopping at the same gas station on my commute. I find one I like and stick with it. I had not previously used their gas at any of their locations (we are in metro Atlanta). For about a decade before that, I’d always stopped at a Chevron on the way into work. And I have always pumped the recommended premium fuel.

Anyway, I could never get the car to run rough in front of my local mechanic (independent shop) so he never attempted to diagnose the problem but he suspected it was a coil pack. There were no codes when he scanned it. He did put in a new main fuel relay (may not be the correct name for the part—it’s a small “relay” that plugs in under the dash on the driver’s side) around that time. The board inside the relay can develop hairline cracks resulting in intermittent performance. EDIT: the part number is 39400-S84-003. It’s about $75 on Amazon.
I switched to a Shell station near work (it’s more expensive, runs $70-$80 to fill the tank here). After a week or so, no stalling or hesitating. Recently, I was in a rush and stopped at the same gas station I had been frequenting when I experienced these issues. I put in $10 of gas to get me where I needed to go. That afternoon it started hesitating on me again. I will not buy their gas for any of our cars if I can help it.

So, using a different gas station (and possibly replacing the relay) fixed my problem.

TRP00

I believe I fixed the problem. I replaced the upstream O2 sensor and the problem has seemed to go away. Thanks everyone for all the help.

Jon M

Congrats. The upstream O2 sensor does adjust the fuel trim. Usually you can see the short term fuel trim at a high + / - on a OBDII reader. Did you have that indication?