Air intake boot cracked - 1990 Lexus LS 400

Hi, I have a bmw aswell, when this happens it is useally that there is a split or crack in the air intake rubber boots, so check those first, and any vacuum pipes that go to the intake, and I dont know how carefull you was when putting the manifold on that a gasket did not seat properly,if you have no problems with all the above check the diser valve is working ok, hope this was some help,all the best.

Vane air flow (VAF) units are a common failure on these cars. It is the the sensor mounted inline on your intake tube that is aluminum and black plastic with a round twist plug. If you unplug it an it runs better that is most likely your culprit. The gentleman above is on the right track. Intake boot cracks/failures are quite common on these older cars too as are the EGR tubes/hoses - listen for air leaks/sucking noises.

The idle air sensor (IAC), made by Bosch looks like a small coke can with two tubes and a plug going to it. Sometimes they are hard to find/hidden under intake. They do go bad, but can usually be cleaned with car/brake cleaner. The internals should rotate; they are just an oscillating valve that regulates extra air to the intake.

You never said it it runs fine once it us up and going. If it does, it could also be a oxygen sensor. You should really consider having the codes read... it really shortens the list of parts to check!

Good luck!
-Scott
www.europartsplus.com

three things to check-idle air control valve if you haven't checked already-a crack or leak in the intake manifold-or clogged ports in your intake manifold

Have to install a new boot, etc or the MAF Sensor
won't work correctly.

Engine has no way to measure air flow input,
with a vacuum leak.

Don't use it, until you correct the issue

Whistle noise indicates a major vacuum leak. Maybe something loose in the intake system. Maybe a vacuum hose disconnected. Will explain lose of power also.

can you keep the vehicle running by working the gas pedal.check the air intake boot for leaks,cracked or torn.

Check your intake boot for cracks (located after the MAF and before the DISA). You may as well Clean your DISA and ICV while you're at it. There's a video on youtube from Xionunjust to show access to the DISA, watch it and he'll show where the intake boot is. Good luck.

Sounds like big vacuum leak.
Check vacuum hoses and intake boot for crackes and proper attachment.
Especially intake boot after air mass meter to the manifold , may be loose clamps.

is your check engine light ON? Has your timing belt been changed? have your intake cleaned, including the IAC valve. Inspect your intake hose for crackes and leaks(this is very typical. If your intake hose is cracked or leaking, this will cause hesitation and rough idling/running. post comments or questions...hopefully this helps

Check the air flow boot from the air filter housing to the intake maniflod for cracks or loose clamps.