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149 Posts
Discussion Starter · #1 ·
04 4.0 has an intermittent idling problem. Idles fine for a while. Then it will bounce between 2000 and 10,000 a few times, then die.
It starts right back up, no problem.
I have sprayed the throttle with cleaner. didn't help.

Is there a module that might be bad?

Knows a couple things...
49,415 Posts
A bad idle can be caused by several potential issues including a bad O2 sensor, bad Throttle Position Sensor, or a very commonly, a dirty Idle Air Control module. The IAC is what provides the engine with ALL of its air at idle rpms, that's the only thing the IAC does. If it gets dirty, it can cause all kinds of idle issues from it being unable to smoothly control the flow of air into the engine at idle rpms.

When you cleaned the throttle body, did you make sure to spray a good quantity of the cleaner into the throttle body at idle rpms? The IAC will only pull the cleaner through itself at idle rpms since that is the only time it is functioning.

The first thing I'd do is remove the air intake tube off the throttle body and start spraying into the TB at idle rpms. The IAC will suck the cleaner into and through itself. The engine will usually die too from the IAC filling with the cleaner but that's ok, just restart the engine. That's actually a good thing since it is indicating the IAC is getting cleaner inside of it and when the engine dies from the IAC being flooded, that just gives the cleaner more time to work on the gunk inside the IAC.

I'd spray a good quarter to a third of a can through the IAC to insure it is clean. Again, make sure you're spraying when the engine is running and at idle rpms. Raising the rpms will cause the cleaner to bypass the IAC. This normally restores the IAC back to good operating condition, seldom does the IAC have to be actually replaced.

If you do that and it doesn't help, the TPS (throttle position sensor) is probably bad and needs to be replaced. It is sealed so it can't be cleaned like the IAC can.

The Idle Air Control Passage Inlet slot, below, is the air intake for the IAC, spray the cleaner toward that with the engine running at idle rpms. Doing so will insure the most possible throttle body cleaner gets into the IAC.


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