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[carterlangley]

Hi guys, girls

Got a small problem.
After (and during) a long (ish) journey, the idling seems to have a mind of its own. It keeps reving up and down and won't settle. While driving I also notice that the engine is reving up and down to keep the speed even on a flat piece of road. This is with cruise control on or with it off.

If I only do town driving then it behaves itself. Only when I do reasonably long trips, say 20miles or longer at a speed of 60 or more.

2000 Grand Cherokee 4.7v8 limited.

I keep on taking it back to the garage I bought it from (Bruce Motors in Aberdeen) to get him to repair this, but he says there is nothing wrong. So......... any ideas on what could be the problem? Hope it is not something drastic like changing the gearbox or something!!

[gazjeep]

Have you tried disconnecting the battery for about 5 mins  :lol:

Fingers crossed  

[Lornaben]

:wink:

[carterlangley]

Got the radio code, and disconnecting the battery doesn't work.
Took my son to work this morning and it was fine. But then the drive is only about 10 miles.

I do know that the lubrication required in the box is quite specialised. If the previous owner skimped and bought a generic substitute could that cause this problem? The transmission overheating light does not come on, so not to sure on that one. It has been looked after by Jeep themselves excepting for the last service.

[Panic mechanic!]

when the engine hunts its usually down to an air leak in the inlet side of things so check all your hoses etc to the inlet manifold., if everything is intact then it could be the mass air flow meter on its way out.
it could come down to something as silly as the air is being drawn threw the spindle on the air flow meter, it may not show on a short journey as the cold start system will be operating til the engine is up to temp.

[carterlangley]

Thanks for that.

My technical ability with engines ends when I open the bonnet and stare in confusion at the contents.
When I come back from offshore in two weeks, I will take it to my nearest mechanic and ask him to check out what you have said might be the problem.

[Mike Pavelin]

when the engine hunts its usually down to an air leak in the inlet side of things so check all your hoses etc to the inlet manifold., if everything is intact then it could be the mass air flow meter on its way out.
it could come down to something as silly as the air is being drawn threw the spindle on the air flow meter, it may not show on a short journey as the cold start system will be operating til the engine is up to temp.

It hasn't got a mass airflow meter.

[carterlangley]

so that would leave it down to intake problems then?

[Panic mechanic!]

ok well throttle body then, i just refer to them as maf's cos thats what i deal with them sorry

[Panic mechanic!]

I would think it is on the induction side yes, the engine hunts because the fuel air ratio is not set and it weakens  then as the rev's rise it either draws more air from the leak or  the  leak is closed by the pressure drop and it richens the mixture

[carterlangley]

so it might be as simple as fitting a new pipe?

[Panic mechanic!]

it could be as simple as a pipe yes , or a sensor

[carterlangley]

Went driving today, and it started its games again.
Tried reving it to see what that did, and she calmed down immediately. Revved her to about 4000. Is that another clue in the puzzle?

[Panic mechanic!]

definitely sounds like a induction air leak to me, but like i said it can be a few things.bubba might be along in a bit to give a view on this as well see what he thinks