Excessive start-up rpms/ erratic idle - possible solution....

[John E Davies]

The other day I cleaned and adjusted the throttle body on my '96 LX450, readjusting the "throttle closed stop" and the TPS. It occurred to me when reinstalling the TB that some folks may have adjusted their throttle and/ or cruise control cables with too little slack. When the engine cranks, vacuum causes the "throttle closer" to suck the butterfly fully closed. If either of those cables is too tight, the butterfly will not shut off completely, giving the engine what is basically an uncontrolled air leak that the idle control circuit may not be able to properly control.

It's real easy to check to see if there is cable slack when the engine is running. Or alternately, with the engine off apply vacuum to the throttle closer (next to the TPS and in line with the throttle shaft) with a MityVac tool to ensure the butterfly is tight closed.

Any thoughts on this?

John

 

[semlin]

wouldn't that lead to a consistently high operating idle?

In favour of your theory I will say that removing the throttle body has cured the start up idle for me for a couple of weeks before, including one occasion when I removed it to clean the EGR intake tube and did nothing to the t-body other than disconnecting and reconnecting the cables and sensor plugs.

 

[loquito]

Has anybody ever just replaced the IAC after the throttle body was cleaned?