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Unread 07-24-2009, 04:31 PM   #1
poobub
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Rough idle after 1/2 mile drive... NEED HELP!!!

Ok, so im new to the TJ forum. I recently sold my XJ and set my eyes on a TJ selling at a local dealership. Its a 98 sahara 4.0 with manual transmission and 82k on the clock. I bought this jeep knowing it had a few issues, but I had jeep fever and im afraid I've gotten myself into a mess. Ok for the problem, after startup I make it about 1/2 mile down the road (usually turning out onto a busy street ) and it seems to lose all power. It bogs down and refuses to take gas under load. I then have to pull over and rev the engine up and down for about 30 seconds to a minute then attemp pulling out once more. After this little issue the jeep will run fine for as long as it stays running. However if I shut it off and go in the store, I come back to the same problem. I am planning on doing a basic tune-up but cannot figure out why this problem only seems to exist shortly after startup and then never again. I have tried to research the forum but have not found any postings with this exact issue. Any help would be GREATLY appreciated.

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Unread 07-24-2009, 04:33 PM   #2
yojeep79
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Check the throttle control sensor. Not saying thats it, but my uncles jeep did close to the same thing and thats what it was.I believe it was like 50 bucks.
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Unread 07-24-2009, 04:37 PM   #3
poobub
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Originally Posted by yojeep79 View Post
Check the throttle control sensor. Not saying thats it, but my uncles jeep did close to the same thing and thats what it was.I believe it was like 50 bucks.
I've wondered about that but is there an easier and cheaper way of checking it other than ******* out $50 just to find out its good?
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Unread 07-24-2009, 04:59 PM   #4
Jerry Bransford
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Before doing anything, buy a can of throttle body cleaner from your local auto parts store and use it according to the directions on the back of the can to clean out the throttle body's interior. The throttle body has a few areas inside that can cause the engine to bog down, especially like the IAC (idle air control) sensor that sucks in air for the engine via the slot above the butterfly valve plate inside the throttle body.

And there's no "throttle control sensor" but there is a TPS (throttle position sensor) in addition to the IAC that can cause problems but it doesn't sound yet like the TPS is your problem.

It could also be a fuel pump issue, or perhaps its running way too rich/lean from a bad upstream 02 sensor. Good luck but start by cleaning the interior of the throttle body.
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Unread 07-24-2009, 05:08 PM   #5
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Originally Posted by Jerry Bransford View Post
Before doing anything, buy a can of throttle body cleaner from your local auto parts store and use it according to the directions on the back of the can to clean out the throttle body's interior. The throttle body has a few areas inside that can cause the engine to bog down, especially like the IAC (idle air control) sensor that sucks in air for the engine via the slot above the butterfly valve plate inside the throttle body.

And there's no "throttle control sensor" but there is a TPS (throttle position sensor) in addition to the IAC that can cause problems but it doesn't sound yet like the TPS is your problem.

It could also be a fuel pump issue, or perhaps its running way too rich/lean from a bad upstream 02 sensor. Good luck but start by cleaning the interior of the throttle body.
I just filled her up yesterday and dumped a bottle of seafoam down the tank. I also have a bottle of TB cleaner that I plan on spraying in it later as well. I have had a few other people with interesting ideas on why they think it could be the fuel pump, and honestly thats about the only thing that seems to possibly make sense. Seems if it were any of your typical idle problems (plugs, TPS, injectors, dirty TB) the issue would continue throughout driving or at least happen at random times. Im gonna go try cleaning the TB and see if that helps any. Any ways to test the pump without actually dropping the tank i just filled up lastnight .
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Unread 07-24-2009, 05:26 PM   #6
Jerry Bransford
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Seafoam in the gas tank won't produce dramatic effects, you really need to go the TB cleaner route to expect much in the way of results if the problem is caused by a dirty IAC or throttle body. You can test the fuel pump by connecting a fuel pressure gauge to the fuel rail next to the fuel injectors. It screws onto the fuel rail's Schraeder valve which is like an oversized tire stem valve, which has a black screw-off plastic cap protecting it. 49 psi is the specified fuel rail pressure so it should be close to that when the engine is running.
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Unread 07-25-2009, 09:00 AM   #7
Jonny Jeep
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I bet it's the O2 sensor. See the link...

97 TJ sputter and stall - o2 sensor?
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Unread 07-26-2009, 12:35 PM   #8
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Originally Posted by Jonny Jeep View Post
I bet it's the O2 sensor. See the link...

97 TJ sputter and stall - o2 sensor?
Hey thanks for the link, not sure how I missed that in my search. I've been doing some other things to the jeep this weekend and have sorta put this issue on the backburner. I did however spray out the TB with no noticeable improvements. I think im going to try unplugging the sensor for a few days to see what happens. I am also not throwing any codes though, thought bad o2's always threw a code. Anyways I priced pumps today in case I end up replacing it ... $287. So im really hoping thats not it. Thanks for all the help so far guys, ill be driving a lot today so ill post tomorrow if the o2 unplugged works.
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Unread 07-27-2009, 04:24 PM   #9
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just wanted to update the post. Unplugged my o2 sensor on Friday and drove around without any issues after numberous starts and stops. I put in the new o2 sensor shortly after and have yet to have any problems. PROBLEM SOLVED!!!! Thanks again for all your help!!!
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