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Unread 11-25-2011, 12:04 PM   #1
schaef89
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2.5L TBI rough idle

I've had a problem with my idle on my 89 wrangler for awhile now and have been trying to get it to run right over the past couple weeks. The problem is that I have a rough idle when I start it up, but it doesn't stumble during acceleration. When I rev it up and let it return to idle it almost wants to stall out and idles around 650rpm. Then after ~5 seconds the idle smooths a little and comes back up to around 800rpm, but is still rough. Same deal happens when I come to a stop sign. Since all the sensors seemed to be worse for wear i started to replace most of them for peace of mind and to try and track down this issue. I replaced one at a time and started the Jeep to see if there was improvement, and so far every replaced sensor has improved how it runs in some way. Here's a list of what I've replaced so far:

o2 sensor (NTK)
MAP sensor
Coolant Temp Sensor
Fuel Injector/O-rings (old one was leaking)
IAC (Idle speed motor)
Removed and cleaned the MAT sensor (seemed to test within spec)
Rebuilt the Throttle body (new gaskets and fuel regulator)
Replaced any vacuum lines that were broken/old looking

My next best guess would be either fuel pump, emissions purge solenoid, or the EGR valve.

Frankly, I have no idea what else it could be. I appreciate and help you guys can throw my way, I'm hoping to get this thing running well by winter.

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Unread 11-25-2011, 01:50 PM   #2
nembudonna
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I've posted this before and got hammered. But all your gas contains Etenhal unless other is stated. Jeeps don't like etenhal. Try getting gas with no etehnal (premium) and a can of heat. You may have to do it more than once. Hope it works. It worked for mine. I replaced all the sensors also, but they needed it.
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Unread 11-25-2011, 02:01 PM   #3
schaef89
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Do I have to keep getting premium and using that heat stuff? Or is it just to clean out any deposits or something? I ask because my brother's TBI doesn't idle like this and he uses regular 89 octane all the time.
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Unread 11-25-2011, 03:54 PM   #4
oldtime_ironman
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I wouldn't bother with the premium stuff. Its a waste of money in a jeep. I just use regular 87 octane, the very cheapest stuff, with zero probs. The HEET doesn't hurt at this time of year - its just to remove any water or condensation from the gas in the tank. I would concentrate on the EGR valve, a rough idle is a classic sign of it leaking. You've already done everything else I could think of, except maybe check how tight are the intake/exhaust manifold bolts? Just winch em down good with a 9/16 socket. Hope this helps!

BTW, EXCELLENT write-up on the TBI rebuild!
.
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Unread 11-25-2011, 04:01 PM   #5
oldtime_ironman
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Quote:
Originally Posted by nembudonna View Post
I've posted this before and got hammered. But all your gas contains Etenhal unless other is stated. Jeeps don't like etenhal. Try getting gas with no etehnal (premium) and a can of heat. You may have to do it more than once. Hope it works. It worked for mine. I replaced all the sensors also, but they needed it.
Not true. Heet, dry-gas, gas line antifreeze, etc. are ALL made of ethanol. That's all it is. Mine does just fine with regular 87 octane and 1x a month it gets a bottle of Heet.

Running premium with HEET is actually too much ethanol, not the other way around.

The stuff you DON'T want is that E85 crap for newer cars. The regular around here has E10 which is actually closer to 7%, but they've been doing that up Northeast here for the last 30 years. Mainly because of winter.

Since Schaef is in PA, he should be OK on the same ol' regular grape juice he's been burning his entire life.
.

Last edited by oldtime_ironman; 11-25-2011 at 04:02 PM.. Reason: op
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Unread 11-25-2011, 04:05 PM   #6
schaef89
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Thanks ironman.. I was thinking EGR myself too. Only reason I didn't think it would need replacing is I replaced it about 3 years ago. Maybe my leaky injector messed with it . I'll have to test it when I get back home from the holidays

edit: I actually just replaced the manifold gasket 2 months prior to this, so that can't be the issue either
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Unread 11-25-2011, 07:38 PM   #7
Xpress
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Running gasoline that "Contains 10% Ethanol" in my Jeep no problems. Replace your PVC and check for vacuum leaks.
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Unread 11-25-2011, 07:39 PM   #8
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Quote:
Originally Posted by nembudonna View Post
I've posted this before and got hammered. But all your gas contains Etenhal unless other is stated. Jeeps don't like etenhal. Try getting gas with no etehnal (premium) and a can of heat. You may have to do it more than once. Hope it works. It worked for mine. I replaced all the sensors also, but they needed it.
The gasolines we have today are LOADS better than they were back when our Jeeps first came out. 10% ethanol won't hurt a single thing. If you wish, you can try an ethanol additive that neutralizes it. Won't change a thing.
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-1996 Jeep Grand Cherokar 5.2L, donor and rainy day driver
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"A well regulated Militia, being necessary to the security of a free State, the [B][I]RIGHT[/I][/B] of the people to keep and bear Arms, [B][I]SHALL NOT BE INFRINGED[/I][/B]."
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Unread 11-25-2011, 10:26 PM   #9
smoan
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check your throttle position sensor mine was doing the same thing and that fixed it
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Unread 11-26-2011, 06:49 AM   #10
nembudonna
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Quote:
Originally Posted by oldtime_ironman View Post
I wouldn't bother with the premium stuff. Its a waste of money in a jeep. I just use regular 87 octane, the very cheapest stuff, with zero probs. The HEET doesn't hurt at this time of year - its just to remove any water or condensation from the gas in the tank. I would concentrate on the EGR valve, a rough idle is a classic sign of it leaking. You've already done everything else I could think of, except maybe check how tight are the intake/exhaust manifold bolts? Just winch em down good with a 9/16 socket. Hope this helps!

BTW, EXCELLENT write-up on the TBI rebuild!
.
I'am just stateing that my 94 runs fine on the regular but when my 90 started runnig bad and got hard to start. I put in the premiun and it started running fine. I still run regular but about every third tank it will start to get hard to start again and I dump in the premium and it clears up. Then I go back to regular. I'am just telling you what worked for me.
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Unread 11-26-2011, 08:05 AM   #11
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Quote:
Originally Posted by nembudonna View Post
I'am just stateing that my 94 runs fine on the regular but when my 90 started runnig bad and got hard to start. I put in the premiun and it started running fine. I still run regular but about every third tank it will start to get hard to start again and I dump in the premium and it clears up. Then I go back to regular. I'am just telling you what worked for me.
Think you need to look at the rig, not the gas bud.

Martin
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Unread 11-26-2011, 08:46 AM   #12
Xpress
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Quote:
Originally Posted by nembudonna View Post
I'am just stateing that my 94 runs fine on the regular but when my 90 started runnig bad and got hard to start. I put in the premiun and it started running fine. I still run regular but about every third tank it will start to get hard to start again and I dump in the premium and it clears up. Then I go back to regular. I'am just telling you what worked for me.
You need to take a closer look. If it runs better on a higher octane gasoline then you have some issues to look for, probably a faulty O2 sensor. Or perhaps it's time for a full tuneup.
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[URL="http://www.jeepforum.com/forum/f12/another-5-2l-yj-thread-1503048/"]My 5.2L Build thread[/URL]

-1989 Jeep Wrangler 2.5L, soon to be 5.2L
-1996 Jeep Grand Cherokar 5.2L, donor and rainy day driver
-2004 Kawasaki KLR650 sunny day driver
[QUOTE=mudsweatNgearz;21162729]Leave em off and weld an I beam on. Bumperetts just scream homo.[/QUOTE]
"A well regulated Militia, being necessary to the security of a free State, the [B][I]RIGHT[/I][/B] of the people to keep and bear Arms, [B][I]SHALL NOT BE INFRINGED[/I][/B]."
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Unread 11-26-2011, 10:22 AM   #13
nembudonna
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It's got all new sensors full tune up with new packard 440 wires everything you can think of. Everything was new and as it had trouble starting and running rough I switched gas and it worked. Also I can get into 5th gear but with the regular I can't. Don't ask me why but it works now and if it ain't broke I'am not fixing it. I knew I was gonna get hammered.
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Unread 11-26-2011, 10:29 AM   #14
oldtime_ironman
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Quote:
Originally Posted by schaef89 View Post
Thanks ironman.. I was thinking EGR myself too. Only reason I didn't think it would need replacing is I replaced it about 3 years ago. Maybe my leaky injector messed with it . I'll have to test it when I get back home from the holidays

edit: I actually just replaced the manifold gasket 2 months prior to this, so that can't be the issue either
Hrmmm. That's oddball. It almost makes me want to say "IAC" because it should be holding steadier than that. But I think you already replaced that, right? And you did the MAP also, right? Its possible the EGR got gummed up already, but wow that was quick. And what is the vacuum line to the EGR like? What is the vacuum reading like at idle?

Only other thing I could think of is to adjust your TPS a bit so It idles about 100 RPM faster, but I don't think its a good idea to mess with that just yet.
.
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Unread 11-28-2011, 08:36 AM   #15
schaef89
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Quote:
Originally Posted by Xpress View Post
Running gasoline that "Contains 10% Ethanol" in my Jeep no problems. Replace your PVC and check for vacuum leaks.
PCV rattles which means it's good. And I've checked all the vacuum lines and replaced the bad ones

Quote:
Originally Posted by smoan View Post
check your throttle position sensor mine was doing the same thing and that fixed it
TPS was replaced this past summer with a new one

Quote:
Originally Posted by oldtime_ironman View Post
Hrmmm. That's oddball. It almost makes me want to say "IAC" because it should be holding steadier than that. But I think you already replaced that, right? And you did the MAP also, right? Its possible the EGR got gummed up already, but wow that was quick. And what is the vacuum line to the EGR like? What is the vacuum reading like at idle?

Only other thing I could think of is to adjust your TPS a bit so It idles about 100 RPM faster, but I don't think its a good idea to mess with that just yet.
.

There's no IAC on these, just an Idle Speed Control Motor.. but yes that was replaced as well as the MAP. I replaced the vac line to the EGR, and messed around with it a little. I disconnected the vac line to the EGR and plugged it, as well as plugging the EGR port. When I did that the idle did not change at all, I'd have to check the book yet to verify if that's bad or not.

I checked the TPS position when I rebuilt the TB and the FSM doesn't really say anything about positioning unless it states it in a different section. It more or less says the computer will sense the idle reading.

EDIT: forgot to add some recent characteristics.. Since I ran it back home to get the hard top (4 hours highway), I had ALOT more power. However, it seems a little doggish during acceleration like it doesn't want to go, but I know it has more power to give. It would also stumble randomly like a misfire or something so that has me thinking fuel pump

I want to thank everyone for the input, It's really helping me out
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