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Unread 06-08-2009, 01:21 PM   #1
Squirrel69
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98 Grand Cherokee with Rough Start/Idle

This is a great site, but unfortunatley I am getting more confused the more I read and try to find out the problem. Basically, my 1998 (6 cylinder) Grand Cherokee is acting like it is running out of gas periodically. It seems to happen more while it is "warming up". I will be going down the road and it acts like it is running out of gas and wants to stall. I put in park, turn off engine. It will start right back up, but will start actine like it is running out of gas again. I changed the plugs and wires. This did make a noticable improvement - although it still does it some - just not as bad as it did. I have also cleaned the Idle Air Controller and intake. This showed no noticable improvement. Another thing worth mentioning, when I start it up the first time when it is cold, it is hard to start. But once the engine has warmed up, it starts up quickly. Please help. I have already taken it to a mechanic who charged me $65 just to say that they don't know what it is.

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Unread 06-08-2009, 01:29 PM   #2
zvanit03ru
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TPS? Ignition coil? Anyone else..?
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Unread 06-08-2009, 08:39 PM   #3
CULate
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The cheapest thhing to do is run some Lucas Injector Cleaner through it. Lucas made a world of difference in our 5.9 after a few tanks of gas mixed with Lucas. I don't have the big money many of you appear to have to throw parts at a problem without being fully sure what is wrong. So I go cheap.
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Unread 06-08-2009, 09:51 PM   #4
SpikeDude
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I'd say clean the injectors like CULate said, my Jeep is rough starting when it's cold. Is your idle real low, like 300RPMs? Maybe check your altinator also.
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Unread 06-08-2009, 10:24 PM   #5
sdowney717
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1998 ZJ 
 
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try replacing the fuel filter

verify the fuel pump pressure and volume. You could disconnect the fuel line at the fuel rail and see how well it flows.
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Unread 06-08-2009, 11:28 PM   #6
UnderTheWooDd
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I had the exact same problem and i just replaced the filter and now it's all good. mine went a step further than yours in that it actually started and then died a few times until the fuel pump pressure burst the clog (at least that's what my meager understanding for fuel systems would lead me to believe). if that doesn't help you might wanna hook up a scan tool if you have access to one, because it could be a problem with your fuel pump. that's my best guess. hope this helps
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Unread 06-09-2009, 07:08 AM   #7
Squirrel69
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This seems to be a common the problem the more I read. However, there seems to be about 20 different things it could be. I think the things worth noting are that new plugs and wires did make a difference (just never made it go away altogether), and that it is hard to starts when cold. There are no codes. I think I will start with the coil, then the fuel filter. Sound right?
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Unread 06-09-2009, 12:13 PM   #8
RyanZJ
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Mine is still doing it and I've replaced the following:
-Coil
-Wires/Plugs
-IAC
-TPS
-Ran two bottles of Gumout Regane and one tankful of Techron through it (this actually helped a TON with smoothing out the idle)

I have a distributor cap/rotor ready to go in tonight, and I'm also going to test the fuel pressure. Hopefully one of those two is the problem, because my last guess is a clogged cat...
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Last edited by RyanZJ; 06-09-2009 at 02:15 PM.. Reason: Forgot that I ran some injector cleaner through it as well...
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Unread 06-09-2009, 12:58 PM   #9
ZJPunk98
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I would also check the first O2 sensor... a bad O2 sensor can cause engine hesitation and possible stallin as the engine is mixing the wrong amount of oxyen and fuel causing odd behavior.
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Unread 06-09-2009, 01:57 PM   #10
jlindseyjr
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Quote:
Originally Posted by RyanZJ View Post
Mine is still doing it and I've replaced the following:
-Coil
-Wires/Plugs
-IAC
-TPS

I have a distributor cap/rotor ready to go in. I'm also going to test the fuel pressure. Hopefully one of those two is the problem, because my last guess is a clogged cat...
I had the same issue (among others), turned out to be a cracked distributor cap. I sprayed a little water on it and could actually see the arc. Now I'm experiencing the infamous "Jeep stall"
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Unread 06-10-2009, 03:48 PM   #11
RyanZJ
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Turns out the new IAC that I put in less than a month ago **** the bed already, so that was keeping my Jeep from idling. Replaced it with my cleaned-up OE unit and it started right up!

Also, I installed the cap and rotor last night. Time will only tell, but I'm willing to bet that my days of rough idle and the CEL are gone. The rotor was bent to hell and there was carbon all over it. It runs like a champ now, I'm loving it!
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Unread 06-10-2009, 08:08 PM   #12
skilled1
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put a fuel filter in it. and see where you are at.
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Unread 06-11-2009, 12:42 AM   #13
UnderTheWooDd
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Quote:
Originally Posted by ZJPunk98 View Post
I would also check the first O2 sensor... a bad O2 sensor can cause engine hesitation and possible stallin as the engine is mixing the wrong amount of oxyen and fuel causing odd behavior.
ah yes but don't forget the MAF
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Unread 06-11-2009, 10:55 AM   #14
Squirrel69
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So this is the update. Autozone talked me out of changing the Ignition Coil saying there would be the code, and said it probably is the fuel pump because it takes a while to start while cold, and needs to build the pressure up. Have 173,000 miles, and original pump. Went and had the fuel pressure checked, and it was 50, what they said is OK. Of course, this was with a warmed up engine. Does it matter if you check the fuel pressure with a hot or cold engine? The jeep did stall on my way home after having the fuel pressure checked (warmed up engine). I am told that the fuel filter is in the tank with the pump, and to change that is going to be over $500. The Jeep seems to be running fine except for this stalling issue. I am not to thrilled about just throwing cash at the mechanie for "diagnostic" fees though. Any more insight?
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Unread 06-11-2009, 11:22 AM   #15
SouthZJ
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Quote:
Originally Posted by Squirrel69 View Post
So this is the update. Autozone talked me out of changing the Ignition Coil saying there would be the code, and said it probably is the fuel pump because it takes a while to start while cold, and needs to build the pressure up. Have 173,000 miles, and original pump. Went and had the fuel pressure checked, and it was 50, what they said is OK. Of course, this was with a warmed up engine. Does it matter if you check the fuel pressure with a hot or cold engine? The jeep did stall on my way home after having the fuel pressure checked (warmed up engine). I am told that the fuel filter is in the tank with the pump, and to change that is going to be over $500. The Jeep seems to be running fine except for this stalling issue. I am not to thrilled about just throwing cash at the mechanie for "diagnostic" fees though. Any more insight?
The PCM can not see when your Ignition coil is bad so you would not get a code

if it just runs rough in idle its often the IAC

(do the key trick) If it dose not start CPS or Cam sensor because there will let the ASD cut out your engine and you would get the code 11 for CPS or 54 for Cam sensor

a wrong working IAC dose not always give you a code but if you get 25 its your IAC

The fuel filter is not in the Tank its infront of it very easy to get there and a cheap fix

The pump sits in the tank and you should first check your pressure befor replacing it

Get yourself registered with jeepunlimited.com then you can use the download area there you can download a rep. manual where you will find how to mesure the resistance of your ignition coil then you can see if it is still good but i would think its a dirty or not right working IAC

I hope that helps and do not buy anything be for you not have checked your codes and or cleand your IAC
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