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Old 09-04-2010, 08:21 PM   #1
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Irregular idle

I have a 97 4 bannger and every time I drive it, at least once it has a rough idle. It evens out quickly. I have changed the spark plugs today and it did it right after I changed them. Any ideas?

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Old 09-04-2010, 08:54 PM   #2
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Rough when you first start it? Hot, cold? After its been sitting for a while? Check the vacuum lines for loose connections etc. Injector cleaner maybe also, if you havent done it in a while.

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Old 09-04-2010, 09:32 PM   #3
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Mine has always had a rough idle, sporadically. I've used parts cleaner and all to check for vacuum leaks and never found anything. Tried changing plugs, which looked perfect still... Tried running seafoam and marvel mystery oil through the fuel system (not at the same time). Cleaned the Idle air sensor. Cleaned throttle body top and bottom side. Replaced o2 sensors.

Nada. Still runs the same as ever even after all that.
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Old 09-04-2010, 09:56 PM   #4
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Did it ever happen when you were accelerating? it has happend twice now when I was pushing on the gas, and had to let up the try again and it finally goes. I think I need to replace the o2 sensors but I can't see them being the problem
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Old 09-04-2010, 10:06 PM   #5
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Your idle speed is controlled by the PCM and IAC. If it only happens at idle clean the throttle body and also make sure you don't have a vacuum leak. It may be the PCM.
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Old 09-06-2010, 11:52 AM   #6
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Quote:
Originally Posted by Fweaky
Your idle speed is controlled by the PCM and IAC. If it only happens at idle clean the throttle body and also make sure you don't have a vacuum leak. It may be the PCM.
i had a 97 4 banger was doin the same it came out to be the iac very simple fix just took time finding it cause i did the same thing you did .. i thought i needed a tune up .. lol
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Old 09-06-2010, 11:58 AM   #7
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My jeep does the same thing, only if it's been sitting overnight. On first start up it's rough and evens out after a few seconds. Could it be the fuel filter?
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Old 09-06-2010, 12:23 PM   #8
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My first two suspicians when confronted with a rough idle are always the IAC (Idle Air Controller, which is not a sensor) and the throttle position sensor. Cleaning the IAC with carb or throttle body cleaner will restore it to proper operation if it was dirty enough to cause problems. Be sure to clean out the oriface (hole) in the throttle body the IAC's solenoid actuated plunger fits into too.

The TPS (throttle position sensor) can get dirty inside and when that happens, a rough idle is the result. Unfortunately the TPS cannot be cleaned like the IAC can, the TPS can only be replaced when it goes bad (gets dirty inside).

The below illustration shows where the locations of these components are for the 4.0L engine but the 2.5L engine's throttle body layout should look the same.
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Old 09-06-2010, 12:30 PM   #9
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Definately take out the AIC motor on the throttle body. I had the same problem with idle in my 97 tj 4l. It's only 2 torx screws to remove it. And you will likely find lots of carbon deposited on it. Also, clean out the bore where it sits. I just used a cloth to get off the big chunks and a tiny bit of carb cleaner (sprayed onto the cloth) to get the rest. Done over 2000k since with more problems. Also had the same problem on my 2001 Pathfinder (don't hate me) several years ago. Same problem, same fix , only on the Pathfinder you have to rip apart half the engine to get at it(argh). I once worked with a diesel mechanic who recommended never to use carb cleaner cause it damages the coating and makes it gum up faster. So use it sparingly.

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Old 09-07-2010, 06:50 PM   #10
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I have a haynes book and can't find anything about an idle air controller, is it mounted on the throttle body?
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Old 09-07-2010, 07:05 PM   #11
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Originally Posted by briancash1013 View Post
I have a haynes book and can't find anything about an idle air controller, is it mounted on the throttle body?
That is exactly why no one ever recommends buying Haynes or Chilton's books, they aren't worth the paper they are printed on for anything more involved than changing your spark plugs or brakes. Yes the IAC is mounted onto the throttle body.
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Old 09-07-2010, 08:24 PM   #12
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I'll give that a try tomorrow, my jeep is sidelined with a flat right now anyway

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