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[ikebaddog]

hi all, sorry if this has been covered before, first of many questions .......After starting my 1998 TJ 4.0auto, the first minute of so it will misfire, doesn't matter if hot engine or cold, as long as its been standing for 10 minutes or so, starts fine, pulls away okay, and then it starts misfiring, if I floor it, it picks up, revs out fine and won't do it again, until switched off for 10 mins or so!
I have fitted a second hand throttle body, with all sensors attached and the fault is exactly the same, two throttle body's with the same fault??? is it that common?

[Mike Pavelin]

Upstream lambda sensor does this, but shouldn't when stone cold, so maybe not. Try running with it unplugged and see.

[ikebaddog]

Cheers Mike, I will give that a try, what should I expect with it disconnected,?

[Jonny Jeep]

With the sensor disconnected either the problem will still be there, in which case it's not the cause of the problem. Or, the problem will vanish, and the fix would be replacing the sensor. I wouldn't have thought being off for ten minutes would allow the problem to recur if it were the upstream O2 as I don't think ten minutes would allow the sensor to cool enough, having said that, it has been a tad nippy of late.

[LairdScooby]

What condition is the engine oil in? It sounds as if the oil is a bit thick and not getting into the hydraulic tappets properly - usually (but not always) accompanied by some clatter from the top end of the engine.

If it's been a while since the oil was changed, do an oil and filter change, preferably using something like Wynns Engine Flush to ensure it gets a good internal clean.

If that improves matters and then the problem comes back in a month or so, add 0.5 - 1.0L of Dexron II to the engine oil. It's amazingly good at cleaning hydraulic lifters/tappets (and the rest of engine too) and has sorted a similar problem i had on mine.

[ikebaddog]

Ok peeps, I have unplugged the lambda sensor, and car now works fine!!, do I need one?

[LairdScooby]

Ok peeps, I have unplugged the lambda sensor, and car now works fine!!, do I need one?

With the sensor disconnected either the problem will still be there, in which case it's not the cause of the problem. Or, the problem will vanish, and the fix would be replacing the sensor. I wouldn't have thought being off for ten minutes would allow the problem to recur if it were the upstream O2 as I don't think ten minutes would allow the sensor to cool enough, having said that, it has been a tad nippy of late.

Going on the previous advice ^^^ i'd say the sensor was dead. Thinking logically about it, the residual heat in the exhaust could be warming the sensor up enough to give the right readings to the PCM while it's switched off so it sounds like the heater in the sensor is dead. Could be wrong of course but the evidence suggests that.

[Jonny Jeep]

The heater would only cause problems during warm up from cold. Any other running problems that go away when disconnected point to the sensor itself being bad.

A new NTK sensor from rockauto.com would set you back about £50.

Sent from my D5803 using Tapatalk

[LairdScooby]

The heater would only cause problems during warm up from cold. Any other running problems that go away when disconnected point to the sensor itself being bad.

A new NTK sensor from rockauto.com would set you back about £50.

Sent from my D5803 using Tapatalk

unless i misunderstood the problem is there from cold but when it's switched off for tn minutes it goes away? It all fits?

[Jonny Jeep]

You're right. I was posting without rereading the thread. I had a thread from jeepforum on my mind I think

Sent from my D5803 using Tapatalk

[LairdScooby]

You're right. I was posting without rereading the thread. I had a thread from jeepforum on my mind I think

Sent from my D5803 using Tapatalk

Thanks for that - thought i had really lost the plot this time lol!

[Delk]

Sorry for jumping on the thread but I have a similar issue with my Jeep and I am not sure if its not the same.

Mine starts and runs fine but if you leave it to idle it gets lumpy and starts to misfire. When its restarted after fits warm it does the same thing. If I drive it around it gets better and acts normal. The engine light comes up now and again and says misfire on whatever random cylinder.

Could this be the O2 sensor?

Its not urgent and I have not had any time to look at it.

[ikebaddog]

Sorry for jumping on the thread but I have a similar issue with my Jeep and I am not sure if its not the same.

Mine starts and runs fine but if you leave it to idle it gets lumpy and starts to misfire. When its restarted after fits warm it does the same thing. If I drive it around it gets better and acts normal. The engine light comes up now and again and says misfire on whatever random cylinder.

Could this be the O2 sensor?

Its not urgent and I have not had any time to look at it.

That sounds almost exactly the same as mine, apart from the engine light coming on, I disconnected the sensor where it plugs into the throttle body connector, the fault has now gone, still no warning light! give it a try, it literally takes a minute

[LairdScooby]

Is your warning light working bad dog? It should come on as a test when you first switch the ignition on.

[ikebaddog]

Is your warning light working bad dog? It should come on as a test when you first switch the ignition on.

Yeah, Check Engine light in red comes on, then goes out when started.

[LairdScooby]

If the light doesn't come on when the fault is there it's unlikely to be caused by anything the system will pick up on so check things like your rotor arm, dizzy cap, leads etc. From memory the rotor arm dizzy cap and HT leads are service items at 60k miles anyway so if they haven't been done in your ownership it could well be the first port of call.

[General Confusion]

We have just spent a while with a similar sort of problem. Turned out to be the fuel pressure regulator.

[ikebaddog]

I'm going to plug lambda sensor back in, I expect fault will come on straight away, we will see!

[Delk]

I had a problem with the fuel pump years ago and it would only happen after the pump got warm and the tank low when you were driving along under load. It would idle fine but would loose power at very bad moments on the motorway.