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Old 09-07-2013, 05:24 PM   #1
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'99 TJ woes...

So I seem to have intermittent issues with my '99 TJ. I'll occasionally have my engine run rough or kinda sputter... usually will happen on longer drives but does happen on short ones once in a while. I'll occasionally have the temp run a little hot... have actually had it spike into the red twice with the check engine light coming on once when it did. I've had the check engine light come on and go off on 2 different occasions other than the one time it did when it ran hot.

Oil level is good and coolant level is low-ish but hasn't moved noticeably in the last month or so. I have yet to do a good fluids change as I've been running ragged at work... no excuse I know.

I do have a leak on what looks like on one of the thermostat lines... where a rubber hose hooks up to a solid metal line. Haven't crawled under to get a better look but will do hopefully this weekend.

Could my thermostat cause the running issues I'm experiencing? Could I have head gasket problem coming up? I've been told to check the mass air sensor... the rough idle goes away when under acceleration.

Woe is me...

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Old 09-08-2013, 03:12 PM   #2
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Also... what would be the cause of sporadic high idle issues? Every now and then my idle will run high to the point where when I put the trans into either neutral or park with motor will rev up and my Jeep will go if I don't get on the brakes.

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Old 09-08-2013, 03:18 PM   #3
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I'm new to jeeps but have worked on my own vehicles for 30 years... I would start with getting a local shade tree guy to help you unless you are comfortable with taking off the throttle body to clean as well as the Mass air sensor.. if the Jeeps mass air sensor is anything like the mustangs that I used to build, be careful, if you damage the thin element you will be buying a new one.
Good luck!
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Old 09-14-2013, 01:37 PM   #4
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Okay so a mechanic friend at work is gonna throw on a pressure tester to see if my thermostat is working or not... plus I think my heater core may be gone since I'm not getting any heat when I try using the heater... that'd probably explain some of the heat and engine issues?
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Old 09-14-2013, 08:05 PM   #5
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If ur not getn heat to the vents it could also be ur water pump going out. I'd keep a very keen eye on ur temp gauge.
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Old 09-14-2013, 09:45 PM   #6
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Flush your system, back flush the heater core and replace the stat as PM. I'd do a full tune-up before looking for that rough running/sputter gremlin...it sounds like your maintenance is lacking. Don't forget about your differentials/tranny/transfer case or someday they'll remind you at the worst possible time.

There's no MAF sensor on these motors.
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Old 09-15-2013, 02:32 PM   #7
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Quote:
Originally Posted by SeVeReDiStOrTiOn View Post
Flush your system, back flush the heater core and replace the stat as PM. I'd do a full tune-up before looking for that rough running/sputter gremlin...it sounds like your maintenance is lacking. Don't forget about your differentials/tranny/transfer case or someday they'll remind you at the worst possible time.

There's no MAF sensor on these motors.
Core was okay but I had a small leak in my radiator... bought a new one and a new thermostat too since when we did a pressure test there was back pressure when we went to release the air... coolant everywhere... my friends thoughts was that the thermostat was probably bad/stuck so that needed replacing as well. Heater works fine and no rough idle or overheating which was probably due to overheating because of the bad radiator and thermostat. Now all I need to figure out is why the high-idle at times. Any idea what would cause intermittent high-idling?

Lacking in maintenance is putting it mildly... not afraid to admit that I've neglected my Jeep since I bought it last year... fluid levels have been watched but never did a change out yet so that'll be a priority.
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Old 09-15-2013, 04:08 PM   #8
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Do a search on cleaning your IAC. Very easy to do. They get dirty and will cause idle issues. Good Luck
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Old 09-15-2013, 08:53 PM   #9
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Bah... dang stumble is back... bought new oil and a filter for my day off on Tuesday... bought a can of throttle body cleaner too.
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Old 09-15-2013, 09:43 PM   #10
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The throttle body is really easy to clean, TJs do not have a MAF (mass air flow) sensor it operates solely on a MAP (manifold absolute pressure) sensor.

Removing the throttle body:
1) Remove the intake hose, phillips screw on a hose clamp and just pull it out of the way a bit.
2) Remove throttle cable, It just clips on. Also unhook the return spring.
3) There are 3 sensors bolted onto the throttle body, carefully disconnect their wiring harnesses, its not overly important to memorize or mark which is which because each has a unique plug.
4) There are 4 10mm Bolts on the 4 corners of the Throttle body, they are all thats left in holding it to your intake.
5) carefully remove the throttle body from the intake and make sure the area below it is nice and clean. If you have to clean it spray some throttle body cleaner, or some seafoam into it. Cover up the intake hole when you're not working on it so nothing falls in.


Cleaning the Sensors:
There are 3 sensors
MAP (manifold absolute pressure)
TPS (throttle position sensor)
IAC (idle air control)

Starting with the MAP:

The map has 2 bolts holding it to the TB, It also has a small vacuum line on the bottom leading into the throttle body. Remove the two bolts and carefully remove the vacuum boot from the bottom. Feel free to spray some TB cleaner through the Vacuum boot don't spray any into the MAP, it operates with a diaphragm to judge vacuum pressure, cleaner can damage that diaphragm and in turn the sensor. Do however wipe it off and clean the contacts for its plug if necessary.


Now for the TPS

The TPS is a pretty simple sensor you can just wipe it off and make sure the contacts for its plug are nice and clean. Don't try to move the internal part as it may cause damage to the sensor. This sensor is generally a works or is broken type sensor not really anything that gets too dirty.


Cleaning your IAC

I usually just spray it off with TB cleaner and give it a gentle wiping. You can cautiously move the plunger back and forth a bit to make sure its not seized. Like the other sensors it's a good idea to check and clean up the connectors.

I like to use a little Di-Electric grease in the plugs when re-connecting them, they have a waterproof seal from the factory but it can only help to be cautious.


Cleaning the Throttle Body:
this is the easy part
With the sensors and gasket off your throttle body is now pretty much just a nice chunk of metal. Soak it down with some TB cleaner making sure to clear out the vacuum hole for the MAP and the side slit and chamber that the IAC fit in. Make sure the main passage is nice and clean top to bottom and the throttle plate is clear of debris and is free to move and fall back into the closed position.

Once everything is nice and clean follow the disassembly steps in reverse.

Either the IAC or MAP could cause a high idle. Another thing to look at is the Vacuum system. a clog or leak could also play havoc on your idle and run quality. Sounds like it may be a good time to seafoam it.

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