Idle speed going through the ROOF on warming up : 97 XJ 4.0 HO

[NeXJ]

Originally Posted by Ecomike

Did anyone check the manifolds to see if they were flat, parallel, true and not warped?

If you hear a sucking sound the same time the idle ramps up, its obviously a vacuum leak. I hear water trigger spray bottle at possible vac leak locations can be informative?

Do not get the TPS wet!!!

If you suspect fuel injection controls, disconnect the IAC, and or TPS and O2 sensor right after cold start up and then see what happens.

thanks Mike - you're the best ... will investigate

[NeXJ]

Originally Posted by old_man

All of the above along with 20 years diagnosing 4.0L's and 50 years of wrenching. When the rpms start to go up, spray some carb cleaner around the intake area and if you see a sudden rpm fluctuation, bingo. Careful of flash back.

Are you using Bellville washers on the intake? If not, do it.

thanks yes - i saw a few things about that on youtube of all places ... i was asking not because i was questioning your ability or 'authority' but i was hoping to learn something ...

[NeXJ]

Originally Posted by Ecomike

In that case it is not a vacuum leak, the ECU is opening the IAC valve to add air. Bad IAT (even if it is new), wrong IAT, bad ground on the IAT sensor???

thanks again mike - it's been too long since i looked into this though i'm not sure that's the case - i'll have to have a look see - i think i was jumping to conclusions at the time though so it could have been an erroneous observation

[NeXJ]

FINALLY took it in for the pros to look at ... this is out of my league of repair i guess ... after the stuff i tried ... any chance this could be due to a badly machined replacement head since I'd just had the head replaced before this (though it ran for several months just FINE before) ...?

i told the mechanic the history and he insisted (without knowing or looking at it) that it was 'going to be expensive' and he seemed to imply it must be due to the head replacement - if i'm not mistaken ...

[NeXJ]

i'd just like to make sure i'm not getting lied to or ripped off ...

[Ecomike]

A pro could figure it out in 1-2 hours for $50 or less in parts. Based on what he said I would have hopped in the jeep and left. I never had any luck with pros, and always had troubling sitting down for weeks after trying them, even when I brought a tube of my own Vaseline.

And they always broke more than they fixed.

It has to be a Vacuum leak or excess fuel. Only so many places that can happen. I don't by a head issue, not all. Warped intake or loose manifold bolts yes. It does not cost $$$$$$$$$s to find and tighten loose bolts.

Did you check the fuel injector to intake port spots for Vacuum leaks???? Could be a bad O'ring on the fuel injector ports?

[smccollamjr]

Agree with Eco, find another mechanic.

[lawsoncl]

Originally Posted by Ecomike

A pro could figure it out in 1-2 hours for $50 or less in parts. Based on what he said I would have hopped in the jeep and left. I never had any luck with pros, and always had troubling sitting down for weeks after trying them, even when I brought a tube of my own Vaseline.

And they always broke more than they fixed.

It has to be a Vacuum leak or excess fuel. Only so many places that can happen. I don't by a head issue, not all. Warped intake or loose manifold bolts yes. It does not cost $$$$$$$$$s to find and tighten loose bolts.

Did you check the fuel injector to intake port spots for Vacuum leaks???? Could be a bad O'ring on the fuel injector ports?

I'd guess intake manifold leak due to loose bolts or failed gasket. Both very easy to troubleshoot and fix.

[NeXJ]

Originally Posted by Ecomike

A pro could figure it out in 1-2 hours for $50 or less in parts. Based on what he said I would have hopped in the jeep and left. I never had any luck with pros, and always had troubling sitting down for weeks after trying them, even when I brought a tube of my own Vaseline.

And they always broke more than they fixed.

It has to be a Vacuum leak or excess fuel. Only so many places that can happen. I don't by a head issue, not all. Warped intake or loose manifold bolts yes. It does not cost $$$$$$$$$s to find and tighten loose bolts.

Did you check the fuel injector to intake port spots for Vacuum leaks???? Could be a bad O'ring on the fuel injector ports?

thanks - well i was wondering if it was the way I explained the problem - and how i'd just got a 'new' head put on - i didnt' explain that it was FINE for a good six months until this problem just SUDDENLY appeared ... but they ARE AAA 'certified' and i've had great experiences with AAA garages in the past. I was explaining to the mech exactly what i tried (IAS sensor, throttle body inspection and clean and other little bits) at which point his eyes seemed to glaze over a bit .. perhaps used to incompetent 'amateur internet mechanics' doing their own stuff - but anyway - well NO - I didn't really want to start opening up the fuel injector rail - it's not something i'm experienced with and I TOO tend to sometimes break more than i can fix so I know when to leave well enough alone - after putting in a new engine and rebuilding the steering box etc several years back I think i'm a bit burnt out on this stuff - it's not really my forte to say the least! Anyway- hopefully they'll do the right thing. If i come up against any huge fees I'll make sure to do my homework beforehand and question anything fishy ... i just hope it's not the computer at fault here ...

[NeXJ]

Originally Posted by lawsoncl

I'd guess intake manifold leak due to loose bolts or failed gasket. Both very easy to troubleshoot and fix.

hmm - wish i'd tried that before - reasonable hypothesis since it had a new head put on and maybe it had 'settled in' since then and changed shape a bit or the manifold did - or the bolts just got a bit loose ...

[NeXJ]

but who knows - as for the 'expensive' comment - maybe they figured my vehicle looked pretty sorry and that no one in their right minds would put in more than a few hundred dollars into it (?) - just had a fire at my place and part of the rear fibre liftgate got scorched as did the tail lights and spare tire on the bumper ...

[Ecomike]

Better hit Walmart and stock up on lots of Vaseline?

[NeXJ]

well we'll see - it's been one week and still not even an estimate - if it's too high and makes no sense then maybe i'll seek greener repair pastures ... though i was reticent to go somewhere else after paying the $120 flatbed fee

[Ecomike]

Its only $4.69 at Target?

https://www.target.com/p/vaseline-pe...E&gclsrc=aw.ds

Originally Posted by NeXJ

well we'll see - it's been one week and still not even an estimate - if it's too high and makes no sense then maybe i'll seek greener repair pastures ... though i was reticent to go somewhere else after paying the $120 flatbed fee

[MickeyS]

but what is normal idle on an immediate idle at cold start? it's differed greatly between vehicles for me.