Folks, my ZJ v8 Chrysler service manual tells not to touch on the set screw that adjusts the minimum throttle opening at idle, aka "idle speed adjustment" back in the carburetor old days.

I took the Throttle Body (TBI out, disassembled and cleaned the idle speed bypass valve, throttle position sensor (which was broken and got fixed and the body itself. It was all nasty covered with black oily mess from the crankcase vent and got shiny as new with some carb cleaner.

My idlr was irregular and high, now it is perfect.

Wrt this set screw, poor manual. Dies not solve the problem of those, like me, bought a used car that has been in whatever unknown mechanic that definitely messed up that screw (tool marks on the TBI casting shows it has been "adjusted").

How are we supposed to adjust this screw, as idle speed is controlled by the PCM, though the idle control valve? In the past i've seen some instruction like a minimum passage on the trhottle plate measured with a wire with some certain diameter. Also had seen " x turns from fully closed"....

Any help? Any harm if I leave it too closed such the idle calve has to be more opened for proper idle?

Thanks!

 

Don't mess with the screw! The PCM controls the idle speed, the timing, and fuel mixture. No adjustments are necessary.

 

Understood I should not touch the screw. This is clear on the service manual as well. Trouble is - the screw has "been messed" for sure! So now what is the fix? Replace the TBI?

 

To my way of thinking, as long as the idle is smooth and steady at 750 hot, don't worry about it. On cold startup, it will run at about 1000 rpm until everything stabilizes, then drop down to 750. If this is happening, the idle air bleed is within the PCM's range of compensation.

 

Back out the screw until the throttle plate is completely closed against the throttle body. Then slowly turn the screw in until you see the throttle plate move ever so slightly. Done!

 

Please describe the conditions with a little more detail? Is it idling wrong? Too high or too low? Is the engine warm or cold when/if idling wrong? If the idle is too low or nearly stalling when warm then your Idle Air Controller (IAC) may be broken. (I think you called it the "idle speed bypass valve")

 

Cherryokee, there is no malfunction after I thoroughly cleaned the TBI with carb cleaner. Idle is fine. Just kept a bad thought as the screw was never supposed to be touched (as per Service Manual), so I thought - "Uh, that screw is probably adjusted at NASA!".

Nick-B, I actually did exactly that in the absence of better support from Chrysler's manual. It does work fine...

My thought was - if I let the throttle too closed, risk would be the IAC totally open and not enough air in (then too slow idle) or too open and with IAC totally closed, too much air and then too high idle.

In doubt I opted for too closed... No idea on the effect of what happens when I gently start pushing the pedal but hey - with a V8 "music" it is being very hard to me avoid flooring at any start on a green light!

Guess this post is done then... unless I find more "scientific info" to post & complement.

Thanks all!