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Unread 07-29-2014, 01:50 PM   #1
gntl2000
Registered User
1999 TJ Wrangler 
 
Join Date: Mar 2014
Location: Tampa, FL
Posts: 3
99 TJ - fast idle with AC on

I have 99 TJ Sport (4.0) with AC. I live in Florida so it's toasty right now. When I first start the engine, it idles and drives fine and continues to do so for about 10 minutes with the AC on. After a while, she'll start idling about 1300 RPM at a light with the AC on. If I turn the AC off, the idle will come down to about 800. It's just strange because sometimes if I leave the AC on, have it in first and start letting out the clutch like I was going to stall it - it will nearly stall. I push the clutch back in and it then might idle fine again for a while. I have fully cleaned the TB and IAC by removing them and really cleaning them out. I normally do this as routine maintenance. I'm thinking vacuum leak but I'm not sure. Any thoughts on where next to look?

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Unread 07-29-2014, 03:13 PM   #2
JWebber
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1999 TJ Wrangler 
 
Join Date: Aug 2011
Location: Lewisville, Texas
Posts: 962
Vac leak or throttle position sensor acting up. I had same problem replaced the TPS. When A/C is running the idle does go up a bit to comp for engine load etc..
But should not go that high.
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Unread 08-29-2014, 02:05 PM   #3
gntl2000
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1999 TJ Wrangler 
 
Join Date: Mar 2014
Location: Tampa, FL
Posts: 3
I think I am going to try swapping out the TPS. I have checked extensively for vacuum leaks and didn't find any. I cleaned out the TB and IAC. I removed the IAC and completely cleaned it. She ran fine for about a week or two and now the intermittent fast idle is back. Should I go with MOPAR original TPS or is one from Advanced Auto Parts fine? What do you think?
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Unread 08-29-2014, 03:15 PM   #4
JWebber
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1999 TJ Wrangler 
 
Join Date: Aug 2011
Location: Lewisville, Texas
Posts: 962
Mopar TPS. Also check the throttle body butterfly and see if it sticks or does not fully close. I used the wrong type of spray fluid once and it dried out my spindle bearings on the throttle body housing. So I bought the right stuff which is for throttle body cleaning and lube. FYI.
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