Topic: Rough Idle, Stumble, Just After Cold Start, 97 TJ

[AWK]

Issue with my 97 TJ , running rough, misfire, stumble, about 15 seconds after cold start.   The Jeep start fine.   I does have an extended crank sometimes but I get around that by turn the key on and waiting for the check engine light to clear, then she fires right up.  This rough idle/stumble issue has just started.   This isn’t my daily driver so I don’t get many miles on  it.
Last November I cleaned the throttle body and clean the IAC passages.   Ran great for the limited use.   In January I took it in and had the recal cal done (e22 reprogram).   Seemed fine after that.   About a month ago it started this miss.   It seemed to be on Humid or wet days.  I sprayed the cap and wires, but didn’t help.   This weekend I put in new cap, rotor, plus and wires.   The Jeep starts great…. then shortly after start up it starts to die out like its being chocked.   I had the cross pipe off the air cleaner when this happened and you can really hear the difference in the suction when the happens… must be the throttle opening.  This goes on for about 1 minute or two.   I can keep it running (barely) by feathering the throttle.  Seems once it get to temp it runs fine.  No issue, no stumble, and WOT seems fine.   There is NO check engine light.  I haven’t tried to see if there are any code (that don’t set the light).   Oh, also back in Nov I added a Dynomax cat back exhaust. 

Any direct will help.

Thank you,  AWK

[grumpygy]

Not sure of your model.  But does it have a Idle control valve on it.  Have one on my 2000 GMC and it was doing something like you are talking about.  Cleaned it up so the surface the plunger rides against was completely clean.  Had to use Qtips to do it.

[AWK]

Yes,  the 2.5 has a IAC.   I cleaned this throughly back in Nov.   Tonight I will check to insure the IAC is working.   I have a niffy little IAC tester, that I have never used.  Got this when a bought a lot of tools at a auction sale.   IF it was consistantly happening I would be looking more at the IAC, but once it gets through this little episode it runs great.  Idles well after a WOT and slow down to a stop.  No stumble, no stall.   It's just that short period until at operating temp (or close to it).

AWK

[grumpygy]

How about your high Idle is that working.  Could be a temp Sensor not working right.

[AWK]

Not sure on the Temp sensor.  Any method to checking that?  Seems logical.

[sharpxmen]

you measure the ohm of the sensor at different temeratures, i don't have the '97 one values but i think it's probably the same as '95, if i have some time i'll dig out the test procedure from the FSM.

another thing that can be is a bad injector, when it does this for about 5 minutes stop the engine and take the spark plugs out - it can tell you if there's a problem with an injector or even a spark issue. I would also test how much each cylinder contributes by removing the injector plugs 1 by 1, if there is one that doesn't change the rpm at all it means that one is not working (the cylinder) and your motor runs in 3 cylinders

I don't think it's the IAC, if it was you wouldn't have an issue when accelerating, once you'd open the throttle the IAC would have very little to no effect.

[sharpxmen]

this is from the '95 FSM, I think they're the same but i am not sure.

ENGINE COOLANT TEMPERATURE SENSOR TEST
To perform a complete test of the engine coolant
temperature sensor and its circuitry, refer to DRB
scan tool and appropriate Powertrain Diagnostics
Procedures manual. To test the sensor only, refer to
the following:
Disconnect wire harness connector from engine
coolant temperature sensor.
Test the resistance of the sensor with a high input
impedance (digital) volt-ohmmeter. The resistance
should be less than 1000 ohms with the engine at its
correct operating temperature. Refer to the Coolant
Temperature Sensor/Manifold Air Temperature Sensor
resistance chart. Replace the sensor if it is not
within the range of resistance specified in the chart.
Test continuity of the wire harness. Do this between
the Powertrain Control Module (PCM) wire
harness connector terminal-2 and the sensor connector
terminal. Also test continuity of wire harness terminal-
4 to the sensor connector terminal. Repair the
wire harness if an open circuit is indicated.

INTAKE MANIFOLD AIR TEMPERATURE SENSOR
TEST
To perform a complete test of the sensor and its circuitry,
refer to DRB scan tool and appropriate Powertrain
Diagnostics Procedures manual. To test the
sensor only, refer to the following:
Disconnect the wire harness connector from the intake
manifold air temperature sensor
Test the resistance of the sensor with an input impedance
(digital) volt-ohmmeter. The resistance
should be less than 4000 ohms with the engine at operating
temperature. The longer the engine idles, the
warmer the intake manifold temperature will become.
Refer to the Coolant Temperature Sensor/Manifold
Air Temperature Sensor resistance chart.
Replace the sensor if it is not within the range of resistance
specified in the chart.

SENSOR RESISTANCE (OHMS)—COOLANT
TEMPERATURE SENSOR/MANIFOLD AIR
TEMPERATURE

Temperature (C / F) | Resistance (Ohms) Min / Max
-40 / -40 | 291,490 / 381,470
-10 / 14  | 49,250 / 61,430
0 / 32     | 29,330 / 35,990
10 / 50   | 17,990 / 21,810
20 / 68   | 11,370 / 13,610
30 / 86   | 7,370 / 8,750
40 / 104 | 4,900 / 5,750
50 / 122 | 3,330 / 3,880
60 / 140 | 2,310 / 2,670
70 / 158 | 1,630 / 1,870
80 / 176 | 1,170 / 1,340
90 / 194 | 860 / 970
100 / 212 | 640 / 720
110 / 230 | 480 / 540

[mrdeath2000]

Is that the test for coolant sensor in the thermostat housing or the back of the block?

[sharpxmen]

Is that the test for coolant sensor in the thermostat housing or the back of the block?

it's the PCM one and yes the one in the thermostat housing, his '97 does not have one on the cyl head towards the firewall but the 91-95 does.

(EDIT: I think they call the other one "Temperature Gauge Sender" or something like that)

[AWK]

Tonight I took the air cleaner off and the started it.   Thought i might see somhthing happen. No issue, but it did set a CEL.   Sat there and ran great.  I check the codes by cycling the key.  Got a  12, 72, and 55.   12 and 55 are understood.   Would a 72 converter code cause my issue?   I did just get the new cal e22 campaign few hundred miles ago.   Converter looks original.   138,500 miles on it.

AWK

[sharpxmen]

if it was the cat it wouldn't be running fine after it warms up,

did you do the pull the injector plug test to see if it's running in 3 cylinders?

i noticed you also said it's doing it more on wet days, maybe the coil has an issue (or the connector to the coil, we've seen that with another member) so check that out.

[sharpxmen]

to answer your question about code 72 (and this is just my opinion so take it with caution): it can mean your cat needs replacement (which is likely anyway given the miles on it) but can also mean the engine is running poorly (so you might not trigger that code with the same cat if it's running fine). You should still replace the cat though if it was never replaced, but i doubt that by doing so it will fix your rough running when cold.

[AWK]

I didn't do any injector test, because it was running fine (this time).   I will check the coil and connections.  In one of your earlier post you said my 97 doesn't halve a temp sensor on the rear of the manifold.  I'm pretty sure this one does.   However,  I  find quite a few things on this Jeep that isn't normal, or evn on the build sheet.
AWK

[sharpxmen]

I didn't do any injector test, because it was running fine (this time).   I will check the coil and connections.  In one of your earlier post you said my 97 doesn't halve a temp sensor on the rear of the manifold.  I'm pretty sure this one does.   However,  I  find quite a few things on this Jeep that isn't normal, or evn on the build sheet.
AWK

that's incorrect - never said manifold on that post (see below), you don't have a gauge temp sender on the cyl head close to the firewall, you only have the one in the thermostat housing - the one in the manifold is for air temperature and not coolant temperature, and you do have it.

it's the PCM one and yes the one in the thermostat housing, his '97 does not have one on the cyl head towards the firewall but the 91-95 does.

(EDIT: I think they call the other one "Temperature Gauge Sender" or something like that)

[AWK]

Ok. Cool.  Read it wrong.   I bought this well used and somewhat altered so I am not to surprised in what I find!