Could a dirty throttle body or a bad IAC cause these issues?

2000 Tacoma 2.4L SR5 — High Idle, Truck Moves Without Throttle, Rumbles on Shutoff


Hey everyone,

I have a 2000 Toyota Tacoma SR5, 2.4L 4-cylinder (2RZ-FE), half cab. I’m dealing with a few issues and would appreciate any input from those who’ve dealt with similar problems.



Symptoms:

• Truck starts fine, but idles high — especially in Park, the RPMs rise even more.
• When I let go of the brake, the truck moves forward on its own up to 10–20 mph, without pressing the gas.
• When I shut it off, the engine does a slight rumble, like it wants to keep running for a second (dieseling effect).
• This started after I changed the spark plugs.
• Mechanic already changed the fuel pump (was only giving 20 psi before), and cleaned the fuel injectors.
• He recommended changing the crank and cam sensors, and noted some air escaping somewhere (suspected vacuum leak or IAC issue).
• I asked about the throttle body and plan to clean it myself soon — also checking for vacuum leaks and cleaning the IAC valve.

Question:



Could a dirty throttle body or a bad IAC cause all of this? Anyone else experience a truck that moves on its own like this when idling high?


Any help or direction would be appreciated — thanks!

 

No experience with an automatic but yes vac leaks can cause high idle and symptoms you have. IAC stuck open can cause high idle as well. Check your hoses carefully for cracks and replace as needed first. Then tackle the throttle body and IAC. Plenty of info here on those subjects so do a little searching here and YouTube. My opinions. Good luck.

 

High idle (if high enough) will cause any automatic vehicle to move on it's own.

Clean the throttle body first. Simple and inexpensive, only use throttle body cleaner, not carb cleaner.

Carefully examine vacumn lines, looking for ones not in place or with split ends. Trim or replace as needed.

 

Replace the throttle positioning sensor.

 

Getcha a fluid trasfer pump and put a cigar on the input side and pump the smoke into the intake system and see if it emerges where it's not supposed to. It might not show anything at all, but its one way to eliminate the vacuum leak side of things.

Also, some diagnostic readings might be helpful in narrowing down the issue

https://www.harborfreight.com/multi-use-transfer-pump-63144.html