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Unread 08-05-2009, 06:03 AM   #1
seanace1
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1997 Wrangler Rough Idle when cold...please help, newbie in distress

Hi all,
Thank you for letting me join this forum, I have myself a new (to me) 1997 Wrangler 2.5l 4 banger with 33 inch tires and a pro comp suspension and 4 inch lift. The truck has 113k on it but the motor runs strong except when it just starts, it idles very rough when cold at around 500 rpms. I did a full tune up including:

New plugs
New Plug wires
New distributor cap
New distributor rotor
New serpentine belt and idler pulley
Oil change with slick 50 high mileage additivie
Lucas fuel injector cleaner (helped a little)
New oil filter
New air filter
Removed and cleaned throttle body and all attached sensors (helped alot w/warm idle, brought warm idle to 750 with slight oscillation but steady)
Coolant flush (muddy as hell before)
Cleaned/tightened batery terminals
Checked battery and alternator both are good at the full range

Now, when I start it it starts every time but sounds rough as hell and still oscillates like crazy down by 500 RPMs. When she is warm she sounds good and oscillates ever so slightly.

Any thoughts/ideas? I thought maybe idle control motor but that looks OK when i took it out, maybe TPS but that looked ok too. I miss the old simple idle adjuster screws, just one turn out is all it would need... Would it be injectors? Thought about the fuel filter but its the entire FPR up by the fuel tanka nd they are hard to find and are not cheap at all...

There is still an annoying clicking sound that I believe is a U joint on the front but thats still to be replaced and would have absolutely no effect on the idle...

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Unread 08-05-2009, 08:49 AM   #2
03JeeperX
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yours sounded like my 03 4.0L I ended up swaping out the TPS and It fixed it mine was wandering at idle for 500-2000RPM. To check mine i started my jeep and unplugged that sensor and it never changed the idle so i changed it and its fixed now
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Unread 08-05-2009, 08:56 AM   #3
Jerry Bransford
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It's likely caused by either a dirty IAC (idle air controller) which is what provides all of the engine air at idle when you're not stepping on the accelerator pedal, or a dirty throttle position sensor. If the problem goes away when you give it a little gas, odds are it's a dirty IAC. If the idle is erratic even when you step on the gas a little, odds are it's a dirty throttle position sensor.

A dirty IAC can be cleaned with an aerosol throttle body cleaner and made to operate good as new, a dirty throttle position sensor needs to be replaced. The IAC is cleaned by just removing the two T-20 torx-head screws that hold it to the throttle body and gently cleaning its solenoid actuated plunger (don't push/pull/turn it) that meters the air into the throttle body with the throttle body cleaner and a rag/toothbrush. Clean the oriface in the throttle body the IAC's plunger fits into too. Clean the interior of the throttle body while you're at it too. If cleaning the IAC doesn't do it, replacing the tps is the likely fix.
tb-tps-sensor-locations.jpg  
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Unread 08-05-2009, 10:13 AM   #4
seanace1
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Well i had taken all of it off and used an entire can of throttle body cleaner to clean out the IAC motor passage way and the IAC motor itself, i also put some seafoam deep creep into it and blew it out with compressed air. I cleaned and dried every bit of the throttle and sensors. It improved warm idle a bit but cold idle when you firsts tart it is erratic. After going down the street to the light and its warm, it idles fine, its only when it is just started it sits at 500 rpms..

Ill try to unplug the TPS today and see what happens
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Unread 08-07-2009, 12:14 PM   #5
seanace1
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If it snot the IAC or the TPS....what else would it be? It is just horrible after a night of sitting and then you start it and sometimes it will dribble out and stall, after you runit for five min its not in danger of stalling but it will slightly oscillate at idle, and throughout the whole power band. You can feel the vibration oscillations through your foot its only a hundred rpm up and down at the most...
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Unread 08-07-2009, 12:47 PM   #6
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Quote:
Originally Posted by seanace1 View Post
If it snot the IAC or the TPS....what else would it be? It is just horrible after a night of sitting and then you start it and sometimes it will dribble out and stall, after you runit for five min its not in danger of stalling but it will slightly oscillate at idle, and throughout the whole power band. You can feel the vibration oscillations through your foot its only a hundred rpm up and down at the most...
"If it SNOT the IAC or the TPS".Jerry B knows all.Do not question the King.
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Unread 08-08-2009, 08:18 PM   #7
seanace1
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Well I replaced both and now it idles alitle high it seems, wat else could it be?
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Unread 08-09-2009, 09:08 AM   #8
HillBilly0324
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Just throwing this out there. There is a Coolant Temp Sensor mo the thermost housing. When it senses the engine is cool it sends a signal to the PCM that the computer uses to keep the engine in an open loop cycle which changes injecter pulse and timing. You might want to check it. Use a digital voltage meter that reads ohms. Just unplug the senser and put one lead to each terminal on the senser. The chart below is the spec it should be at depending on what temp the coolant is at. Just for your info the specs and procedures to check the Intake Air Sensor are the exact same. Hope this helps.

ECT Sensor and IAT Sensor
F* Min-Max Ohms
68 11,370-13,610
77 9,120-10,880
86 7,370-8,750
104 4,900-5,750
122 3,330-3,880
140 2,310-2,670
158 1,630-1,870
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Unread 08-10-2009, 05:45 AM   #9
seanace1
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I will have to try that...After reaplcing the TPS and IAC it got better but not all the way.. It idles fine for a while but its idling around 1000 and I think it should be lower... After about 5 mins of idling it starts to oscillate again but still not as bad. As far as the intake temperature sensor, when standing on the drivers side of the engine bay, past the throttle body on the right of the intake manifold there are two fittings, one im guessing is the intake temp sensor which has an electircal plug/fitting and the other is like an air tube fitting. Which is which? Also in the valve cover on the same side on the left is an air hose fitting, and another on the top to the right that looks like a PCV valve to me, but every book I have seen say these dont have PCV valves...

Thank you all so much in advance for the help
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Unread 08-10-2009, 09:58 AM   #10
Jerry Bransford
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Unplug the upstream 02 sensor and see if that affects the symptoms. If it does, it could just be a bad 02 sensor that has been the problem all along.
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Unread 08-10-2009, 12:52 PM   #11
seanace1
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Where is that O2 sensor located?
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