Celica Forums General Discussion Engine and Performance Running Lean with poor throttle response

I'm very new here and I just got my 2000 GT a little over a month ago. The check engine light came on and I got the P0171 code. I changed the spark plugs and oxygen sensors but the check engine light still said it was running lean.

Here's what it does:
When you first start it, it will idle rough for about 3 to 5 seconds. Then it will accelerate itself and idles fine. It only does this when you start it for the first time in several hours. If I start it, shut it down, then start it again, it will not idle rough the second time.

The other problem is that it has not great throttle response. It isn't terrible but it down take a second or 2 for it to accelerate like it should.

I have changed the oxygen sensors, the spark plugs (but not the plug wires or coil packs) and the fuel filter.

The car runs well with virtually no problems. But I want it to run perfectly. How can I get rid of that poor throttle response so it will accelerate right away?

All help is appreciated. Thank you.

did u find out an answer to your problems?

Yoshie,

Did you solve your problem?

Any solution to @aaronlehunt7? We seem to have identical problems. Got the car a few months back. I have been chasing a fix for weeks and I am at my wits end! Started with P0171 code. First fixes were:
Replacing a destroyed air filter
Cleaned a horribly dirty MAF sensor
Replaced spark plugs.
Replaced leaking valve cover gasket.

New code appeared. P0300 and very rough at cold start. Idle smooths out after a few minutes and drove pretty decent but not very peppy.
Removed and cleaned Throttle body.
Cleaned and reconditioned fuel injectors.

Still rough idle with cold start. STFT and LTFT showing lean condition. 13 -19% total. I also could hear slight sucking sound from in or around Intake Manifold when opening the throttle body to simulate acceleration.

Replaced Intake Manifold gasket yesterday.

Sucking sound and engine hesitation much worse on simulated fast acceleration. Fine with slow acceleration, but if I accelerate quickly, major sucking sound from in or around Intake Manifold.
Still running lean condition.
I am tired of throwing parts at the car, but I am a stubborn DIYer and trying to avoid a trip to the mechanic if possible.
So, I either created a better vacuum with the gasket repair and fuel/fire can't keep up? Or there is a more pronounced vacuum leak elsewhere? Vacuum line, maybe? Could insufficient fuel pressure cause that sucking sound on acceleration? Any thoughts on what to try next would be greatly appreciated. Please ask clarifying questions as well. Thanks.

P0300 is random misfiring.

if you replaced with new spark plugs then the problem may be bad ignition coils or ignition cables. The coils may look OK and work fine at high RPM but may be old, bad parts, insulation may have leaks after so many miles and won't fire adequate energy at low RPM.

Check and clean the ignition coils, clean the coils' contacts and the cables' connectors, make sure they make good contact. Swap the coils around to see if the problem improves.

Clean and tighten all grounding points on the battery, engine and chassis.

Buy all electronic parts only from

https://densoautoparts.com

About $40 a coil Except may BOSCH and DELPHI, all other Chinese copies and counterfeits will fail after may be 20K miles.

Good luck.

Thanks for the response CAPTAINSOLO. I swapped a known working MAF sensor and my numbers improved a bit, so I have one on order. I'll update when it is installed. Did you mis-type that website? Seems like the letter "i" does not really belong in it and I don't want to go to the wrong place. Thanks.

Sorry mistyped:


https://densoautoparts.com/

Unfortunately, the new MAF sensor did not make an appreciable difference. I will go on to check coil packs, wires and do some more vacuum checks. Thanks.

Check the airbox. Make sure it is properly assembled and tightened down correctly. My Lexus had a P0171. Turned out I put the air filter in backward and the box was not completely closed. After the air box is reassembled, the code never came back.

Check vacuum hoses from the airbox to the throttle body. They are black quarter inch rubber.

If any is loose or leaky, car will idle rough and accelerate poorly and jerkily.