Revs fluctuate at low rpm and engine will stall - and loss of power, revs out.

[toddconklin]

Hi, tried searching on this but I can't put all the pieces together. Read a bit about 1/4 tanks of petrol, "cps's" etc but I can't work this out (not suprising I don't know much about wrenching).

Ok, this is an intermittent problem but quite frequent.

The revs will start fluctuating between about 400rpm and 1000rpm at idle or low rpms - after a fairly short time they will just fall too low and she'll stall. This happens even whilst driving - as soon as you take your foot off the pedal it will behave in the same manner - so makes no diff whether in drive or park or neutral.

The strange thing is that at the same time, I lose power and if you accelerate the the revs just climb way up but no corresponding power (it feels like you're riding the clutch with it mostly disengaged and then working the accelerator at the same time - if it was a manual). I have no idea whether this is a coincidence and I don't know if it ALWAYS happens when the revs start faltering but is a definite relationship somehow.

My mechanic had a quick look at the car and reckoned it may be just cause I was running regular unleaded (worked engine - see note below). I put premium in and it seemed to make all the difference in the world but the problem is happening again and I'm sure I filled it with premium.

I'm going to try to drain the tank and refill with premium just to be sure, and check it's not full of water or other crap but I can't really think what else to do. Please help.
It happens at all fuel tank levels. I can't check error codes as I think the instrument cluster and whole dash has been replaced with an earlier model as there is nothing digital and it just looks old.

Thanks heaps.

Note: The engine has been worked so is probably a little more sensitive to octane levels. Bit of a summary on engine: compression boosted a little (shaved head), new cam or something for more low down grunt, power chip, high flow air filter, extractors and full sports exhuast.

[Jonny Jeep]

Pre face lift Cherokees still have the ability to show codes you just need to count the check engine lamp flashes. http://www.allpar.com/fix/80s-codes.html

How's the battery? bad batteries or even bad connections at the battery clamps can cause a whole load of weird issues. Remove the clamps and clean up the contact surfaces on the battery posts and clamps. And charge the battery up and get it tested if you can. Just to make sure all is OK there and you're not just chasing ghosts.

[cantab27]

don't know if this helps... when my tps went bad mine would stall out, the trans shifted all over the place....would idol for about to mins and stall...always would start up but... had a idea it was tps so parked next to a mates xj and swap them over ,it worked so went out and brought a new one .......good luck........

[rainman]

If my heap was doing this I would:
^ what he said about the battery, Then check the earth for the computer is clean and tight. under where the loom plugs into Computer. As well as the earth from the fire wall to the Block, and from the battery to the block. Clean and tight. As stated above bad earth connections can cause all kind of symptoms.
After that:
Download the manual and test the TPS.
I would also pull out the IAC and clean it up and test it as well.

[toddconklin]

Thanks guys that's great. Just charged the battery up a couple weeks ago but could very well be dead - looks nice and new but one of those ones that has an indicator light on it - says if no light it needs replacing and there's no light... Will check connections too.
As far as earth and stuff I might need to ask a few more questions but I'll get stuck into it soon and see how far I get. No idea what a TPS is or an IAC but I'll check into it and report back.

[Hanoman]

We have always run our XJ on Premium since new. Recently I noticed rough running at idle, so decided to change from our usual supermarket fuel to BP premium, and guess what she is running smooth as silk again. Must have picked up a bad brew.

[toddconklin]

Ok I know I'm probably gonna get flamed for this but how do you get the fuel out of the tank? The fuel tank bash plate has no access hole for anyplug in the tank and it doesn't seem to easy to pull the bash plate off. Before I go to the trouble, can anyone confirm if there is a way to drain the fuel tank once I get the bash plate off? I would prefer not to siphon it out cause then I won't get any of the crud out that may be in there.