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Old 07-05-2010, 04:07 PM   #1
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Slightly high idle (~1100rpm)

A quick history... I was having some slow acceleration issues for the past few weeks so I cleaned my TB, IAC pindle and replaced the TPS (the TPS was reporting a 10-70% throttle). The new TPS also reported a weird throttle range (15-69%) so I purchased another off of Rockauto after giving them the OEM model number that I got from the dealer. They guaranteed that it would then be the right model TPS for me. Oddly enough even that TPS reports the same throttle range but the Jeep drives ok. Today I started to notice a high idle, about 1100rpms. I noticed that the idle increases when I turn my AC on (this causes an abnormal noise and vibrations that can be felt through the Jeep) or when I pump my brake pedal hard while not moving.

I'm going to try my old TPS again and see if this problem still occurs. I'm also curious if the extreme heat today could be causing this (it's about 90F outside). I've read the main culprits for this can be the IAC, TPS, ECT, MAP or a vacuum leak but I don't want to just throw parts at this. I've attached a sample data log from my scanner of the engine at idle and when I engaged the AC (had to upload to megaupload, forum only allows picture attachments).

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You can see that the idle increases slightly along with the MAF pressure and even the throttle position. Could anyone analyze this and perhaps point out anything that doesn't look kosher? Do some of these values look OK? My ECT reports the coolant to be 203 after idling for 10 minutes in the baking sun. My temperature needle never seems to go past 210 even in heavy traffic. My IAT also seems to be pretty high.

I lean towards replacing the TPS back to the old one because the throttle position increases when I turn the AC on and I don't think the computer could change the throttle position %, just the idle RPM via the IAC, is that a good assumption?

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Old 07-08-2010, 06:24 PM   #2
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A little update... I took it for a drive after writing this thread to see if I could get the high idle to repeat; it wouldn't happen. Since then, every time I start it after its been sitting for a while (in morning before work, when leaving for work, etc) the idle will pulse up to 1100rpms for a minute or so and go away once I start driving it around. Could this be the ECT or MAP acting up? Does anyone have a resistance chart for the ECT or what units of vacuum the MAP should report?

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Old 07-08-2010, 06:25 PM   #3
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Quote:
Originally Posted by MikalCarbine View Post
A little update... I took it for a drive after writing this thread to see if I could get the high idle to repeat; it wouldn't happen. Since then, every time I start it after its been sitting for a while (in morning before work, when leaving for work, etc) the idle will pulse up to 1100rpms for a minute or so and go away once I start driving it around. Could this be the ECT or MAP acting up? Does anyone have a resistance chart for the ECT or what units of vacuum the MAP should report?

Mine does that too. it's just to warm up the engine.
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Old 07-08-2010, 06:46 PM   #4
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I can't remember mine ever doing it... it makes sense though because my Saturn would do something similar
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Old 07-08-2010, 07:09 PM   #5
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Are you running the A/C? The compressor kicking on and off will cause fluctuations in rpms. Also just FYI having your heater selector on the windshield will also cause the A/C to work. It helps remove moisture from the air and defrosts the window quicker. I case you didn't know.
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Old 07-08-2010, 07:15 PM   #6
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Sounds normal to me, most vehicles go onto "high idle" when first started up and then will drop back down to normal after warming up a bit.

The ac being on will also cause I slight increase in idle from my prior experince with a few different vehicles.

With that being said, I will be the first to admit that I'm no pro, but nothing you mentioned would cause me to every think twice about it
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Old 07-08-2010, 07:36 PM   #7
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Whenever you replace an important sensor you need to reset the computer back to default. Otherwise it's still trying to interpret the data thinking it's the old one. Poor computer gets confused, poor driveability results. Eventually it will learn, but it can take many many miles.

Clearing codes does NOT reset it to default. Scanners cannot reset it - they just clear codes. There are no "quick and easy tricks."

It needs a "deep cleaning" of the memory. Disconnect the battery and LEAVE IT DISCONNECTED FOR AT LEAST 10 HOURS. When you restart it the computer has been reset back to factory specs. It'll learn from there like it was a new one with new sensors.

It may take a few miles - 5-10 - to relearn everything, but it will.
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Old 07-08-2010, 07:58 PM   #8
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Quote:
Originally Posted by rrich View Post
Whenever you replace an important sensor you need to reset the computer back to default. Otherwise it's still trying to interpret the data thinking it's the old one. Poor computer gets confused, poor driveability results. Eventually it will learn, but it can take many many miles.

Clearing codes does NOT reset it to default. Scanners cannot reset it - they just clear codes. There are no "quick and easy tricks."

It needs a "deep cleaning" of the memory. Disconnect the battery and LEAVE IT DISCONNECTED FOR AT LEAST 10 HOURS. When you restart it the computer has been reset back to factory specs. It'll learn from there like it was a new one with new sensors.

It may take a few miles - 5-10 - to relearn everything, but it will.
That's one thing I neglected until I realized it today. When swapping from my AZ TPS to my RockAuto TPS I only pulled my cable for a minute or so and put it back on. I just did a ten minute clear but I'll do an overnight one tomorrow. I was talking to the stealership yesterday about the TPS range not being correct and they said something about clearing the ECU with a special scanner, something a battery pull wouldn't do and they wanted $94/hr to do it! I read briefly in my FSM that all of the sensors' grounds tie into one pin of the ECU, does anyone know where this ground is located? I haven't had the time to do any reading on it yet

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