Rough idle, power loss

[rosszh]

The XJ is playing up lately, usually after a cold start, about 400m down the road or at the first stop sign / lights it will start idling rough and loosing power, I usually have to shift into park or neutral and give it a tiny bit of throttle to keep it from sputtering really badly but unless I really jam on the acceleartor this is only a partial fix as it's still trying to sputter, has also done it while moving (ie. after I pull away from that first stop). This generally keeps up until I'm moving again at decent speed (50-60+ kmph) at which point it seems fine at further stops.

I replaced O2 sensors, TPS, IAC and plugs ~ 8 monthes ago. It always starts without hesitation, and haven't done anything different to it or with it recently.

Bringing it in to load test the battery today (about 3 years old) and will have a look at the throttle body tonight and give it a good clean if needed.

Only other thing I can think is that it had/has a noisey cat but I just assumed it was a rattly heat shield on it.

Any thoughts on anything else it could be and how I can check it? Vacuum lines, etc?

[Dustbowl]

It's the TPS!!!! They're about as water and heat resistant resistant as newspaper

[rosszh]

forgot to mention, it's a 97 classic auto

[rosszh]

It's the TPS!!!! They're about as water and heat resistant resistant as newspaper

So a clean should do it? or you think the actual sensor has crapped out in less than a year?

[Dustbowl]

So a clean should do it? or you think the actual sensor has crapped out in less than a year?

It's very possible, especially if you wheel it a lot...
It's a good idea to give those terminals a clean with some WD

[rosszh]

started it when I got home today and just let it idle in the driveway, after about 4-5 minutes it started idling like crap, just for the sake of it I let it go to see if it would stall but it doesn't just sits there sputtering, it evens out after I give it a bit of throttle again. Checked the throttle body and it's still clean, so I'm out of ideas. Picking up a scan tool online maybe it will give me a trouble code, it's not throwing any on the CEL though.

Battery also load tested ok

[mtd]

check the o2 sensors. When my upstream sensor went bad it was making it idle rough. Might be it might be not but worth a check.

[rosszh]

check the o2 sensors. When my upstream sensor went bad it was making it idle rough. Might be it might be not but worth a check.

will disconnect it and clean it off, both 02 sensors got replaced with all the rest of the stuff, but yeah worth a look

[Roler]

Initially I was intended to suggest the CPS, since that could cause some issues like yours. However, it starts fine, left idling and then after a few minutes the idle goes rough and then picks up again with a bit of throttle. Feels like a heat related issue, O2 sensors could be one reason. Doesnt sound like bad IAC either. Leaking injectors usually give a rough idle on start up when they clear the excess fuel. Fuel pressure?

[rainman]

disconnect oxy sensors and see if it still does it.

Checked for codes?

[FRANKIDOWNUNDER]

How are your spark plug leads?. I had a problem with rough running on my ZG and it turned out to be a crook plug lead, (original ones still there after 16 years). Fitted a new set of after market ones and all problems went. Might be worth looking at.

frankidownunder.

[Dustbowl]

Crap temp sensor will effect your idle, and it's get up and boogie

[genericuser]

Check your distributor and rotor button for wear.

[rosszh]

Cheers for the advice guys, will start ticking things off the list. Also have an OBD2 scanner on order.

What will happen if I unplug the oxy sensor? Will it fix the rough running but trip the CEL? or will it make it run rough?

Have noticed some leaking around my thermostat housing that's calcified on the block so looks like a new temp sensor and housing is in order, probably a new thermostat as well while I'm there but the existing one's probably only 2 years old.

Did the leads and plugs less than a year ago so should be all good. Will pop the dizzy and check the rotor though as it doesn't like the sea air much and could be corroded.

I would have thought most of these would cause ongoing issues though, not this one-off issue on start up then fine. Ie. it happens everytime I start the car but once running it doesn't seem to occur again after the first hiccup.

[rosszh]

another thought, Exhaust Header>? It seems to be making a bit of noise under heave acceleration, best I can describe it is when you stick your tongue out and kind of blow raspberrys, but it's hard to tell how loud or where from as I'm driving when I notice it, not overly loud but I'm pretty sure it never used to make that noise.

[rainman]

disconnecting the oxy will make the computer run off pre programmed fuel maps. will use more fuel than when utilising a correctly working oxy-sensor.
so disconnect take for a spin, re connect take for a spin, see if the problems disappear then reappear.

then you have to decide if the sensor is shot or cracks are letting air in causing the (perfectly serviceable) sensor to give bum readings to the PCM.

it may not be the oxy sensors at allbut it is cheap to test and easy to rule out.

[rosszh]

disconnecting the oxy will make the computer run off pre programmed fuel maps. will use more fuel than when utilising a correctly working oxy-sensor.
so disconnect take for a spin, re connect take for a spin, see if the problems disappear then reappear.

then you have to decide if the sensor is shot or cracks are letting air in causing the (perfectly serviceable) sensor to give bum readings to the PCM.

it may not be the oxy sensors at allbut it is cheap to test and easy to rule out.

Thanks for the info, will give it a go. I remember the pigtail on the upstream o2 sensor being a $#@* of a thing to get plugged in all the way, so could have something to do with it if it's come loose or gotten corroded.

[Jonny Jeep]

The symptoms are typical of a bad heater element in the upstream O2 sensor. When the heater is bad the sensor isn't up to temp when the computer starts using it to sense fuel mix and the erroneous data means the computer misfuels the engine. When the exhaust gases heat the sensor to within it's operating range the data becomes accurate and the engine smooths out.

Disconnecting the sensor in this case would make the engine run smooth and it should only be slightly rich. It may trip a code, it may not. If you have a multimeter you can measure the heater element resistance across the two wires that are the same colour. IIRC it should be 5-7 ohms.

[rosszh]

The symptoms are typical of a bad heater element in the upstream O2 sensor. When the heater is bad the sensor isn't up to temp when the computer starts using it to sense fuel mix and the erroneous data means the computer misfuels the engine. When the exhaust gases heat the sensor to within it's operating range the data becomes accurate and the engine smooths out.

Disconnecting the sensor in this case would make the engine run smooth and it should only be slightly rich. It may trip a code, it may not. If you have a multimeter you can measure the heater element resistance across the two wires that are the same colour. IIRC it should be 5-7 ohms.

Just to confirm, it is the Oxygen sensor, thanks to Jonny Jeep for the explanation as well!! I'm just running it disconnected at the moment and problem has cleared, have a new 02 sensor on it's way from Rockauto, will try a bosch one this time rather than the standard motors one that I ordered previously. Happy that it's a $30, 15 minute problem, not an 8 hour $1000 one, knock on wood, means I can save my $$'s for fun mods and not repairs.

[Jonny Jeep]

I've used Bosch in the past without problems, changing it when i replaced a broken cat, but many in the US find that Bosch sensors don't work well in Jeeps. In case the Bosch sensor needs replacing in future, NTK are the OEM supplier to Jeep and generally recommended. I probably would have mentioned it last week if I wasn't away from home and on my mobile.