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  #1  
Old January 7th, 2018, 21:56
ert01 ert01 is offline
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Idle drops when HVAC controls are adjusted

History:
2001 XJ
0630 Head (freshly rebuilt)
Totally redone cooling system
New battery
New fuel pump
Otherwise itís pretty stock

When the HVAC is set to defrost, the jeeps runs fine. When itís changed to most other positions, the idle drops really low (like 400or less) for a bit (maybe 10sec) before it comes back up to normal.

Swapped IAC and MAP sensor and TPS with known good ones from my other jeep. Same issue.

Checked for vac leaks and found a crack in the cruise control line so I replaced it. Same issue continues. But cruise always worked fine anyways.

Iím thinking itís gotta be something vac related but Iím running out of ideas... and I thought a vac leak would increase idle wouldnít it?

Any help?
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  #2  
Old January 7th, 2018, 21:59
ert01 ert01 is offline
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Re: Idle drops when HVAC controls are adjusted

Maybe related, (I’ll let you be the judge); but it’s always had a long start condition. It’s odd... doesn’t go away when I prime it multiple times. Still a long start. Only seems to start nice when it’s sat for a long time. Like 2 weeks. Overnight or over a weekend and it still has a long start. But let it sit for weeks on end and it’ll fire after the first crank.

I replaced the fuel pump thinking it was weak or the check valve in it was failing but that wasn’t it.

Anyways, like I said, I don’t know if it’s related...
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  #3  
Old January 8th, 2018, 15:07
Afireinside Afireinside is offline
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Re: Idle drops when HVAC controls are adjusted

Defrost bumps the idle up because the a.c. compressor is running.
Good luck
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  #4  
Old January 8th, 2018, 18:19
alwayzAMC alwayzAMC is offline
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Re: Idle drops when HVAC controls are adjusted

long start could be a few things, dirty IAC dirty coolant temp sensor, and the fuel pressure regulator that snaps into the top of your fuel tank would be the first things i would check, especially if there is no check engine light on. also i think 400 rpm is a bit low for when your a/c clutch is engaged, if you haven't i would also take a look at your ground wires, my 2000 is very fussy with ground wires, especially the ground to the inner fender.
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  #5  
Old January 8th, 2018, 19:17
ert01 ert01 is offline
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Re: Idle drops when HVAC controls are adjusted

I'll start looking into a few of those things.... but I forgot to mention that the AC is deleted. No compressor... just the delete pulley on it for now until we have funds to do a full AC service in the spring.

I could believe that the coolant sensor could be dirty... it had a cracked head when we got it (hence the 0630 swap) and I don't recall changing that sensor out when we changed the head so I'll definitely swap it for a new one.

Also I'll definitely check the ground wires... The whole engine came out when we did the head swap so I'll make sure they got hooked up OK.

I thought the pressure regulator was integral in the pump? Is it separate on a 01?
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  #6  
Old January 9th, 2018, 05:35
alwayzAMC alwayzAMC is offline
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Re: Idle drops when HVAC controls are adjusted

do a google search for a fuel pressure regulator, it snaps into the top of your fuel tank, it is a seperate unit, you can test if it is functioning by hooking up a fuel pressure guage, start the jeep you should have 49 psi, after you confirm that shut the jeep off, if the pressure drops after it is shut off your regulator is suspect. irc it should stay at almost 50 psi even after several hours after it is shut off.

your coolant temp sensor will likely not need to be replaced, just clean any sludge off of it with a bit of fine grit emery cloth.
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  #7  
Old January 9th, 2018, 06:47
HttpWayne HttpWayne is offline
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Re: Idle drops when HVAC controls are adjusted

Quote:
Originally Posted by Afireinside View Post
Defrost bumps the idle up because the a.c. compressor is running.
Good luck
He's right. The chances are your idle is just low and it only seems normal to you when the ECU bumps it up when the AC compressor is turned on (defrost does that).

You can take out the IAC and try to clean in. Mine just sat for over a year and that think was almost welded shut. I had to PB blast and heat gun that mofo a lot to get it to move millimeters at a time. Most people just have one that needs sprayed with carb cleaner to free up the carbon deposits.

Hard starting could be IAC related, but I would think you would have an easier time after it's been warmed up. I know with the coil packs in the 00 and 01 you had to have heat shields put under the fuel rail to insulate them from those god-forsaken cat-converters right under the manifold. If you tried to start it up after the vehicle warmed up and it sat for a few minutes (they call it heat soak, the fuel inside gets too hot and causes pre-ignition, and I bet running a higher octane would stop that). I myself have a 2000 and I am tossing those things out next week when I get my head reinstalled. I'm just going to extend the O2's for the post-cat back to a normal cat setup in the rear. It sounds like you live in a cold environment so I doubt that is your issue at the moment.

What does your voltage gauge read? It wouldn't hurt to check the fluid levels in your battery and top them up with distilled water if they're low.
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  #8  
Old January 10th, 2018, 15:30
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Ecomike Ecomike is offline
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Re: Idle drops when HVAC controls are adjusted

What other issues does it have?

Have you tested the TPS voltage at idle?

You may still have a vacuum leak, disguising a low idle, in the HVAC system.

How does it run once started?

I would suspect low fuel pressure. Have you inspected the spark plugs for fouling, or for signs it is running it too lean?

Have you run a vacuum gauge test at various operating conditions?
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34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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  #9  
Old January 10th, 2018, 20:15
ert01 ert01 is offline
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Re: Idle drops when HVAC controls are adjusted

Quote:
Originally Posted by HttpWayne
He's right. The chances are your idle is just low and it only seems normal to you when the ECU bumps it up when the AC compressor is turned on (defrost does that).
AC compressor is deleted currently. Idle is usually around 900rpm IIRC...

Quote:
Originally Posted by HttpWayne
You can take out the IAC and try to clean in. Mine just sat for over a year and that think was almost welded shut. I had to PB blast and heat gun that mofo a lot to get it to move millimeters at a time. Most people just have one that needs sprayed with carb cleaner to free up the carbon deposits.
Cleaned the replacement when I put it in from my other jeep. Wasn't too bad at all... just a fine film of black on it. No thick sludge or crunchy buildup at all.

Quote:
Originally Posted by HttpWayne
Hard starting could be IAC related, but I would think you would have an easier time after it's been warmed up. I know with the coil packs in the 00 and 01 you had to have heat shields put under the fuel rail to insulate them from those god-forsaken cat-converters right under the manifold. If you tried to start it up after the vehicle warmed up and it sat for a few minutes (they call it heat soak, the fuel inside gets too hot and causes pre-ignition, and I bet running a higher octane would stop that). I myself have a 2000 and I am tossing those things out next week when I get my head reinstalled. I'm just going to extend the O2's for the post-cat back to a normal cat setup in the rear. It sounds like you live in a cold environment so I doubt that is your issue at the moment.

What does your voltage gauge read? It wouldn't hurt to check the fluid levels in your battery and top them up with distilled water if they're low.
Has a brand new battery in it... but I did a check just to confirm and everything looks good. Right around 13.6V

I'm in Canada and our version of the 00/01 doesn't have the 2 mini cats (at least this one doesn't... maybe there's different emission packages up here?) It has just the one further downstream beside the transmission.

Quote:
Originally Posted by alwayzAMC
do a google search for a fuel pressure regulator, it snaps into the top of your fuel tank, it is a seperate unit, you can test if it is functioning by hooking up a fuel pressure guage, start the jeep you should have 49 psi, after you confirm that shut the jeep off, if the pressure drops after it is shut off your regulator is suspect. irc it should stay at almost 50 psi even after several hours after it is shut off.

your coolant temp sensor will likely not need to be replaced, just clean any sludge off of it with a bit of fine grit emery cloth.
Looked at some on google... looks like it's right on top of the fuel pump on the 00/01's at least. The replacement pump I put in definitely had a new one on it as I didn't swap any parts from the old pump over to the new one.

I will do a bleed-down test and see what turns up. I could imagine I might have a stuck injector though that might be leaking past. Fuel mileage is pretty poor at the moment and injectors are already on the todo list. But they'd probably have nothing to do with the idle drop/HVAC... I'm thinking they might have something to do with the long start, but the idle/HVAC issue is the biggest concern at the moment since we've been dealing with a long streak of cold weather up here.

I'll be sure to pull and clean the coolant sensor though. I bet it got grimed up when the old original head went.

Quote:
Originally Posted by Ecomike
What other issues does it have?

Have you tested the TPS voltage at idle?

You may still have a vacuum leak, disguising a low idle, in the HVAC system.

How does it run once started?

I would suspect low fuel pressure. Have you inspected the spark plugs for fouling, or for signs it is running it too lean?

Have you run a vacuum gauge test at various operating conditions?
No other issues that I can think of... low idle when HVAC changed, long start, poor mileage (but so far i've been accounting that to the -30C weather we've been having).

No I haven't but I can definitely do that. What should it be reading?

I'm also thinking vacuum leak too somewhere... but I was always under the assumption that a vaccum leak would cause a high idle, not a low idle?

It runs great when started. Feels smooth, powerful, no stutters or hesitation. Shifts are all good. Drives very nice overall.

I'll pull the plugs this weekend and look. I haven't checked them since I finished the head swap so I probably should do that anyways.

I don't have a vacuum gauge but I can easily get one... I'm thinking I could just plumb on into the intake manifold somewhere so I can see what's going on in there. Unless theres a better place to tie it into that you can recommend?
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  #10  
Old January 10th, 2018, 22:13
trippled trippled is offline
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Re: Idle drops when HVAC controls are adjusted

An easy check would be to just plug off all the vacuum lines running to the cruise and HVAC stuff at the intake and retest. If it's still there then you know it's not vacuum related.

Depending on the size of the vacuum leak,the computer can see a change in map (less vacuum) and interpret that as load, which would cause the pcm to add fuel. Which could actually drop the idle.
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  #11  
Old January 11th, 2018, 08:14
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Ecomike Ecomike is offline
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Re: Idle drops when HVAC controls are adjusted

Low fuel economy could be a problem with the O2 sensor, or wiring to it.

You need to see if the O2 sensor signal is running lean, or rich, or if it is not switching properly. There is a great thread here I wrote years ago on testing with a multi meter, on the DC volt scale 0-1 volts or O2 sensor signal, heater and sensor wire ground tests.

But on the low idle it sounds like you have a vacuum leak when the AC is in defrost mode, and the IAC closes to try and compensate, then when you switch HVAC modes the leak is gone, and it takes the IAC valve a while to adjust the idle back up. Vacuum leaks can be just about anywhere under the hood or dash.

Check the rear CCV tube orifice on the top rear of the valve cover and see if the orifice is partly plugged.

I would also test the CTS temp sensor at your temp extremes for proper resistance for the hard starting issue and the IAT intake air temp sensor, after cleaning it.
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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  #12  
Old January 12th, 2018, 12:12
ert01 ert01 is offline
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Re: Idle drops when HVAC controls are adjusted

That makes sense... I'll check on those things this weekend.

I have the Autoenginuity connector and software package and it shows me the graph output of the O2 sensors (which shows high and low points as well as the frequency and the average reading) so testing the O2 sensors is pretty straightforward for me to do. I did suspect the O2 sensor already so I graphed the output of it a week or so ago... I'll try to attach that file tonight when I'm home and maybe you could let me know what you think? I understand the basics of how the O2 sensors work and how that whole system affects fuel ratio, but I'm unsure of what readings are normal and what shows a weak O2 sensor. It's not bad enough to trip an engine code, but again, I don't know where that threshold is set in the ECU for it to trigger a CEL.
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