***December 2002 build date, TJ2 Magna Sports Sedan with about 190,000km***

My vehicle has two issues. I'd love to hear some opinions about possible causes, etc.

Issue one

On cool mornings after the vehicle has been sitting overnight, the engine starts reliably 100% of the time, but often stutters and almost stalls when I accelerate from stop. After 30 seconds or so it drives normally. What could be causing this issue?


I use 98 octane fuel almost 100% of the time.
The in-tank fuel pump and fuel filter replaced about 5 months ago.
Spark plugs (including tube seals, rocker cover gaskets) and leads replaced about 5 months ago.
Distributor cap, rotor and o-ring replaced about 5 months ago.
Throttle body cleaned about 5 months ago.
Two oil changes (including flushing and filter) in past 9 months (only traveled 2 or 3 thousand kms)


Issue Two

When the vehicle is idling in drive the RPM sits at around 500 and the motor sounds slight rough (not terrible but no the best either). 500 RPM is clearly to slow...

When the vehicle is idling in neutral the RPM sits at around 750 and the motor purrs smoothly.

Both conditions occur whether the A/C is running or not with the RPM changing reliably between 500 and 750 when switch between the 2 gears.

Is there a way to correct this behaviour, what could it be?

Thank you in advance :)

If the oxygen sensor has never been replaced, it could be starting to fail... to test, disconnect the sensor (connector is on passenger side of centre console just above the floor about level (vertically) with the dash), reset the ECU (by disconnecting/reconnecting the battery or unplugging/replugging the ECU connectors) and test drive. If the behaviour improves, the sensor is potentially suspect; if no change the sensor is still probably okay (though at that mileage it is about due to die).

Also, are you sure of the revs? The lowest marking on the tacho is actually for 600rpm not 500rpm. Of the several cars I've checked with Evoscan, the tachos seem to be not particularly accurate below 1000rpm. In gear with the engine fully warmed up, I would expect the engine to idle at 625rpm with A/C off and 650rpm with A/C on; in neutral 700 and 800rpm respectively.

If the oxygen sensor has never been replaced, it could be starting to fail... to test, disconnect the sensor (connector is on passenger side of centre console just above the floor about level (vertically) with the dash), reset the ECU (by disconnecting/reconnecting the battery or unplugging/replugging the ECU connectors) and test drive. If the behaviour improves, the sensor is potentially suspect; if no change the sensor is still probably okay (though at that mileage it is about due to die).

Also, are you sure of the revs? The lowest marking on the tacho is actually for 600rpm not 500rpm. Of the several cars I've checked with Evoscan, the tachos seem to be not particularly accurate below 1000rpm. In gear with the engine fully warmed up, I would expect the engine to idle at 625rpm with A/C off and 650rpm with A/C on; in neutral 700 and 800rpm respectively.

Oops, oxygen sensor,... I totally forgot that I had also replaced that about 5 months ago. I've lost track of everything I've done to this vehicle. So that being said, it probably isn't the culprit, but thanks for suggesting it, as I really do appreciate you trying to help me.

In regards to the tacho, even though the 500 and 750 RPM are not actually written on the gauge, I make the assumption that the RPM is 500 when the needle is half way between 0 and 1000. Likewise with 750RPM, when the needle is a further half way between that point and 1000. Although technically it is probably not that accurate, it is consistent when changing between drive and neutral.

In short I'd like my engine to rev more consistently at what I believe to be the 750RPM level at idle no matter if it is drive, neutral or reverse.

The big question is what makes it change down to 500RPM when placed into gear?

The big question is what makes it change down to 500RPM when placed into gear?

The extra drag the torque converter places on the engine. In neutral the engine can spin freely, in drive or reverse it's pressurising the tranny fluid in the torque converter and placing torque on the driveline. Revs will always drop when placed into gear in an auto.

The extra drag the torque converter places on the engine. In neutral the engine can spin freely, in drive or reverse it's pressurising the tranny fluid in the torque converter and placing torque on the driveline. Revs will always drop when placed into gear in an auto.

It's just that when I pull up to traffic lights ,etc and the engine idles in drive at 500RPM it feels somewhat rougher then I would like. I would much prefer if it idled at 750RPM in drive as it feels much smoother.

Do you think it would be possible for a skilled mechanic to adjust the idle to my preferences via tweaking/reprogramming of the ECU or some other reliable method?

Thank you for your advice. :)