Were is the idle air part on the engine? And is it separate or attached to another part?

Tiny
ANGGIE
  • MEMBER
  • 1999 DODGE CARAVAN
  • 210,000 MILES
Trying to take the Idle Air Part out to clean it, but can't find it on the engine.
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Saturday, October 15th, 2011 AT 8:11 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
Cleaning won't help. What's the symptom? Was the battery recently disconnected?
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Saturday, October 15th, 2011 AT 8:34 PM
Tiny
ANGGIE
  • MEMBER
It runs fine when its cold, but when it gets warmed up it starts to act up and run rough. The guy at the parts store said to clean that part before having to replace it to see if it fixes the problem. He said he did it to his car and it worked.
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Saturday, October 15th, 2011 AT 8:39 PM
Tiny
CARADIODOC
  • EXPERT
Very bad advice from a parts guy. There's no arguing with success but there's a lot of different things that cause the same symptoms.

Your automatic idle speed motor is bolted to the side of the throttle body. It only controls the amount of incoming air that flows through a passage around the throttle blade. At the same time the Engine Computer adjusts the position of that motor / valve, it also adjusts how long the injectors stay open during each pulse. That is done strictly to control idle speed. Above idle, that motor and valve have no function, and it definitely will not cause a rough idle. It can only cause an idle speed that's too low. Also, any problem the AIS motor or passage would cause will be there all the time, not just when the engine is warmed up.

You can also prove the AIS motor is working by observing its action at engine start-up. Without putting your foot on the gas pedal, the idle speed will "flare up" to 1500 rpm, then come right back down to around 800 rpm. If that occurs, the automatic idle speed motor is working and the air passage is not plugged. With the better detergents in the fuels today, I haven't needed to clean any of those passages in many years. That used to be a common repair.

I asked if the battery had been disconnected recently. If it has been, the Engine Computer has to relearn "minimum throttle" before it will know when it must be in control of idle speed. Until then, the engine will usually die at stop signs and fail to start unless you hold the gas pedal down about 1/8". You won't get that idle flare-up either.

For running rough, the first thing to check is if there's any stored diagnostic fault codes and whether the Check Engine light is on. Those codes will get you to the circuit or system that needs further diagnosis. Failing MAP sensors can cause a rough running engine but they don't fail very often like they did in the late '80s. '96 and newer vehicles have misfire detection built into their computers. When they're detected, the Check Engine light will turn on and there will be a code stored that will list which cylinder has the problem.

The next thing is to start is with the basics, spark plugs and wires, especially if it's an intermittent problem, and a compression test if the misfire is always there. Other less-common causes include a plugged fuel pickup screen in the gas tank. The clue is the engine will run fine at highway speed when less fuel is being pumped and it will stall at lower speeds, particularly coasting, when more fuel is being pumped. Chrysler has extremely little trouble with injectors so they should be one of the last things to suspect.

If you have a steady misfire, you can slide a grounded pick between the spark plug wire and boot to cancel one cylinder at a time to see which cylinder is causing the problem. Another approach is to connect a scanner that can display live sensor data during a test drive. You can see what the Engine Computer is seeing but it usually takes an experienced mechanic to interpret those readings.
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Saturday, October 15th, 2011 AT 9:09 PM
Tiny
ANGGIE
  • MEMBER
We have changed the spark plugs & wires already. Also the throttle positioning sensor. It runs fine when its cold but after running it for 30 plus miles and warming it up it runs bad. Sputtering like its miss firing and the engine is running rough.
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Saturday, October 15th, 2011 AT 9:22 PM
Tiny
CARADIODOC
  • EXPERT
Next time it acts up, leave the engine running but stop and momentarily loosen the gas cap. If the running problem clears up, the vent in the cap may be stuck. That's real rare but it's always the first thing we think of. That might make the Check Engine light turn on too, and a diagnostic fault code "large evap leak detected" may be set. You can ignore that and it will erase automatically after starting the engine 50 times.

Sorry to say the throttle position sensor won't cause that problem either. Any bad connection, even intermittent, will turn the Check Engine light on and set a related code. If the sliding contact is making poor enough contact, you'll have a hesitation or stumble on acceleration. That can happen when speeding up, not just when leaving a stop sign.

Your description is sounding more and more like a plugged pickup screen in the gas tank. That isn't real common but when it does happen, it can be really hard to figure out. It happened on my '88 Grand Caravan a number of years ago. Took me four hours to nurse it all the way through Minneapolis road construction, but once I got on the highway and kept it over 55 mph, it ran fine for over 150 miles until I had to slow down for my turn-off, then it stalled again. Knowing now what the cause was, a clue would have been found by unplugging the vacuum hose from the fuel pressure regulator and plugging it. That would have caused fuel pressure to go up and there would likely have been a little black smoke from the exhaust, but the increased restriction would have reduced the amount of fuel being pumped and that needed to get through that sock in the tank. The more immediate clue is the faster you drive, the better it runs. Also, it takes a little while for that pickup sock to collapse and become blocked. 30 miles is just the right amount of time for that to show up. Once the problem acts up, it will stretch back out and open up if you let it sit for 10 or 15 minutes with the engine off, then it will run fine again for a few minutes.

Has anyone checked for stored diagnostic fault codes yet?
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Saturday, October 15th, 2011 AT 11:38 PM

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