Topic: Rough idle

[JMcJeep]

I have one other problem with my 97 Jeep Wrangler SE that I hope to fix.  Everytime I start it up, whether it's in morning cold or after driving it for a while, it will idle perfect for about 30 seconds or so and then will run rough for a few seconds and then smooth out.  As long as I let it do its thing before I take off, it never hesitates or stumbles.  But if I try to accelerate before I wait for it to clear the rough idle, it will hesitate, stumble, and sometimes even backfire before it finally clears up and everything is good.  Not sure what to do.  Any ideas?

Thanks.....

[Jeffy]

I'd clean the TB.  I'd try to recover the error codes to see if it picked up anything.  My guess though, would be IAS.  It's allows air to get past the throttle valve when it's closed and the engine starts up initially.

[JMcJeep]

I didn't think about the IAS.  I had already cleaned the throttle body, hoping that it would make a difference but it didn't.  I'll have to check it.  

Thanks for the help!!

[Jeffy]

If you cleaned it without taking the sensors out you could have pushed crud into the IAS.  BTDT.

[sharpxmen]

I had the same problem and it turned out to be the throttle position sensor - it cost  me $60 for a new one.

[lanulos89]

60 bucks sounds a bit steep for a tps i think i paid around 30 for mine.

[sharpxmen]

oops, that would be Canadian dollars :-) but still, lot more than yours.

[JMcJeep]

I had already put a new throttle position sensor on it.  I hope to replace the Idle Air Control sensor this weekend to see if that will take care of my problem.  I do love my Jeep but problems like this will just drive you nuts!!

[Jeffy]

Once you get on top of all the little maintanance you'll be fine.

[JMcJeep]

Well, I was finally able to change out my IAC motor on the throttle body the other day.  I thought I was good to go.  It started up, idle down as it should and it didn't stumble.  The next morning I started it up and about 20 seconds later, I have the rough idle for a few seconds and then it smooths out.  I just couldn't believe it!!  One thing about having this problem, my wife will not go anywhere with me in my Jeep until I get it fixed.  She's worried that it will die one day and leave us stranded.  Me, I'm not too worried about that.  I'm beginning to wonder if maybe the fuel pressure regulator is not holding the fuel pressure after turning the Jeep off but then again it does it when I turn it off for a few minutes and start it right back up.  Surely it wouldn't be losing pressure that quick.  Is there something else that I've missed that needs to be checked?  
Thanks for any help you can provide on this one!!

[Jeffy]

I'd try this next time.  See if there are any error codes.

To get the codes from your 1997 TJ:

   1. Turn the ignition key ON THREE TIMES in succession:
      ON : OFF : ON : OFF : ON
      (within FIVE seconds)
   2. Count the number of times the check engine lamp on the dash flashes. The number of flashes represents the error code. There will be a short pause between the flashes representing the different digits of the code. Longer pauses separate individual trouble codes.
   3. Code 55 will be the last code to be displayed.

11     No crank reference signal detected during engine cranking. Intermittent loss of either camshaft or crankshaft position sensor. CKP sensor target windows have too much variation.
12    Direct battery input to PCM was disconnected within the last 50 Key-on cycles.
13    No difference recognized between the engine MAP reading and the barometric (atmosphere) pressure reading from start-up.
14    MAP sensor input above or below acceptable voltage. 5 volt output to MAP sensor open.
15    No vehicle speed sensor signal detected during road load conditions.
17    Engine did not reach operating temperature within acceptable limits. Engine does not reach 20º F. within 5 minutes with a vehicle speed signal.
21    Upstream oxygen sensor response slower than minimum required switching frequency. Upstream oxygen sensor heating element circuit malfunction. Downstream oxygen sensor heating element circuit malfunction. Downstream oxygen sensor input voltage maintained above the normal operating range. Oxygen sensor voltage too low, tested after cold start. (Upstream or Downstream) Left oxygen sensor input voltage maintained above the normal operating temperature.
22    Engine coolant temperature sensor above or below acceptable voltage.
23    Intake air temperature sensor input above or below acceptable voltage.
24    Throttle position sensor input above or below acceptable voltage. TPS signal does not correlate to MAP sensor.
25    A shorted or open condition detected in one or more of the idle air control motor circuits. Actual idle speed does not equal target idle speed.
27    Injector #3, and/or 4, and/or 5, and/or 6 output driver does not respond properly to the control signal.
31    An open or shorted condition detected in the A/C clutch relay circuit. Insufficient or excessive vapor flow detected during evaporative emission system operation.
33    An open or shorted condition detected in the duty cycle purge solenoid circuit.
34    An open or shorted condition detected in the Speed Control vacuum or vent solenoid circuits. Speed control switch input below the minimum acceptable voltage.
37    Relationship between engine speed and vehicle speed indicates no torque converter clutch engagement. An open or shorted condition detected in the torque converter part throttle unlock solenoid control circuit. Incorrect input state detected for the Park/Neutral switch. Auto only.
41    An open or shorted condition in the generator field control circuit.
42    An open or shorted condition detected in the auto shutdown relay circuit. An open condition detected in the ASD relay output circuit. An open or shorted condition detected in the fuel pump relay control circuit. An open circuit between PCM and fuel gauge sending unit. Circuit shorted to voltage between PCM and fuel gauge sending unit. No movement of fuel level sender detected.
43    Peak primary circuit current not achieved with maximum dwell time. Misfire detected in one or more cylinders 1 thru 6. (4 and 6 cyls.)
44    Battery temperature sensor in voltage above or below acceptable range.
46    Battery voltage sense input above target charging voltage during engine operation.
47    Battery voltage sense input below target charging during engine operation. Also, no significant change detected in battery voltage during active test of generator output circuit.
51    A lean air/fuel mixture has been indicated by an abnormally rich correction factor.
52    A rich air/fuel mixture has been indicated by an abnormally rich correction factor.
53    PCM Internal fault condition detected.
54    No camshaft signal detected during engine cranking.
55    Completion of fault code display on Check Engine lamp.
63    Unsuccessful attempt to write to an EEPROM location by the PCM.
64    Catalyst efficiency below required level. (Same as code 72)
65    Power steering high pressure seen at high speed. (2.5L only)
72    Catalyst efficiency below required level. (Same as code 64)
77    Malfunction detected with poser feed to speed control servo solenoids.

[JMcJeep]

I checked the codes yesterday and the only codes that came up were 12 and 55.  Nothing close to giving me information on my problem.  I don't know if this has any connection to this problem but I have a pretty significate amount of power loss when running the air conditioning.  I know this is a 4 banger and will never have a lot of power but I find it hard to believe that this was happening when this Jeep of mine was new.  I don't think anyone would have bought the thing if they were test driving it with the air on.  Each time the compressor kicks in, it feels like you just backed off of the gas a little.  Then once the compressor disengages, it returns back to normal.  It really bogs it down!!  Does this sound normal to you?  Somehow, I'm going to get this Jeep running right if I have to replace every part related to the ignition or fuel system.  Thanks for trying to help!!

[Jeffy]

Compressor?  So you're saying it has A/C and that's when it gets slugish?  

2.5L's weren't really designed for having A/C.  Some YJ's had it but it was a Dealer installed option and did not come from the factory that way.  Since the 2.5L shares all of the front accessories as the 4.0L, they used 4.0L parts on the 2.5L.  The worst was if you has A/C and an Automatic.  The Auto already wastes a lot of power because of the way it's designed.  Add A/C and it becomes really slugish.

Now with the TJ's, I guess A/C was popular and everyone sorta expects it these day's.  A/C was a standard option from the factory.  It stills bogs the engine down though.  The A/C system should have a vacuum controlled idle boost control.  (I don't rememebr the exact name.)  What it does is bumps the RPM's up at idle when the A/C is on.

Hope that helps.

[stickerhead]

I just read this post and my 97 does the same thing.  I have checked codes, nothing. After reading all the responses, what fixed it?  is it electronic parts or fuel pressure problems?

[agood1]

My 97 also does the exact same thing....has to be some type of sensor or fuel pressure problem.  I just replaced my cylinder head and I checked the intake while I had it off and throughly cleaned the throttle body and the IAC....so I know that is not the problem.  I have also changed the plugs, wires, dist. cap and rotor.  Nothing helped.  I am thinking injectors or sensors......anyone else been able to resolve this issue?