Austinian

I have just started having some acceleration problems from idle in my 1997 LS400. It starts and idles fine, cruises fine, but hard acceleration causes a noticeable hesitation before kicking in.
The hesitation is sometimes brief, sometimes for a few seconds. In the longer ones, the car is obviously laboring before suddenly it kicks in.
It went away for a week, then came back today. i also got a check engine light, and the code is for fuel mixture/airflow.

Suspecting my sensor, I checked and cleaned it. No change. But, heres what I found (PHOTO INCLUDED).
When I open the hood and manually race the throttle from idle, a part of the vacuum system that is near the airflow sensor hesitates before distending a small belows. i don't know the name of the part, couldn't find it identified in any diagrams, so I'v included a photo -
Just under the belows is a small arm that is hard-linked to the throttle, when the throttle is revved, the arm responds by dropping down, away from the bottom of the belows. Whatever valve is in the belows follows the arm down. Here's what I observed -
The valve follows (opens? closes?) erratically, as if its gummed up or stuck. On a hard rev, if the valve immediately drops with the hard linked arm, it revs normally. If the valve/belows DOESN'T drop, it sound like the engine is struggling to suck enough air and makes a throaty sound in the air intake. The instant the little vacuum valve drops, the throaty sounds stops and the engine races up instantly.
So..
What is that little vacuum valve?? Is it getting stuck in the up position because of grime or some sort of added friction? Sometimes, it goes up and down freely and the engine accelerates normally. However, most of the time there is that little sticky hesitation and the first instant of a hard acceleration is bogged down till it frees up.
Can the path or mechanism be cleaned?
Any ideas??
THANKS!!!

AHJ

Hi
If you give us the code, there are usually troubleshooting steps in the manual
Some guesses:
- Check the closest vacuum line - it has electrical(?) tape on it. Is it to stop a leak?
- Clean the throttle body
Good luck

dicer

Looks like a dashpot to let the throttle close slower, mostly used on vehicles with automatic transmissions.
Code is for things like MAF, ECT, O2 sensors. ECU

Austinian

All right, my code is P0172, rich fuel mixture, which felt pretty obvious when it bogs down.
However, its still intermittant. It will accelerate fine for a bit, stopping and starting, then with no other indicators, at the next light it will do the hesitation bog-down on initial acceleration.
Would this be a problem at the intake? Is the too rich fuel indicator more likely a lack of oxygen (which is what it sounds like when revving), or is the air fine but it'sdumping in too much fuel?
Anyone run into this and find a solution? I'll search the forum as well and do my due diligence...

sha4000

iTrader: (1)

Maybe a dirty MAF sensor.