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Old 11-17-2013, 01:18 PM   #1
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Abrupt on/off throttle

My throttle is very light switch like at slight openings. This is a 2004 4.0 TJ. Worse when cold, but there all the time. There is no easing into it. Replaced the TPS some time back because of low power/loss of power at certain throttle positions, and it fixed that problem, but still have the abrupt on/off. Does the IAC have any effect on slight throttle opening. Idle seems to operate fine. Revs tend to hang up a little on gear changes when cold, but when up to temp, that goes away. Anyone else had this?
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Old 11-17-2013, 02:43 PM   #2
Knows a couple things...

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That very well could be the IAC hanging up. I'd use some aerosol throttle body cleaner to clean the IAC's plunger and the oriface in the throttle body that the plunger fits into.

You might be able to clean it well enough to fix the problem (if caused by the IAC) by spraying the cleaner into the throttle body opening while the engine is running. The IAC itself is what needs cleaning and it only draws air in through its opening in the throttle body at idle RPMs so try to keep the engine RPMs at or close to idle so the IAC can draw as much of the cleaner through it as possible.

The slot the IAC draws its air through at idle RPMs is the Idle Air Control Passage Inlet shown below. That's the slot that should get as much of the cleaner through as possible. Spraying at the slot while the engine is running will likely kill the engine but that's ok, just restart it. You want the IAC to get as much of the cleaner past it as possible. Doing it this way eliminates the need to actually remove the IAC to clean it... which of course isn't as thorough but it normally does the job well enough to cure such problems.

Again, no guarantees your problem is caused by the IAC but I agree with you that it's about the most likely source of the problem at this point.
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