High idle only with AC on.

I have a situation that seems to happen when hot and only when the AC is on. The idle is @ 1500rpm and actually increases to @ 2000 when I apply the brakes. The transmission is still pushing away until the jeep is almost stoped, then the idle drops to normal. Turn the AC off and all is normal.
I have a 99 - automatic - bored throttle body
I searched the posts and found a recent thread that mentioned the TPS as a possible place to check. I figured I would post my experience, being it is a different year jeep and different cause, with the hopes someone out there knows what is going on.
This happened once last summer/fall and never happened again until today.
Thanks.
Eric

Thats funny because right as my compressor was going out, my 90 was doin the same thing. I figured it was because of my crap compressor but maybe not.

man what a coindicence, just had the same thing happen on my 99 as well. Only not that high. Yesterday as a matter of fact. Was very noticeable too. Started the engine, backed out of my driveway (engine was fully warm) and i cut the a/c on and as i was idleing out of my driveway, RPM's actually dropped, down to about 500 i'd say. But then it bounced back up. Thought maybe i had some dirt in the gas or whatever and it was just burning it off. Got down the road and went to stop and i noticed rpm's were at 1000 now, with my foot on the brake and in drive. Popped it in neutral and they went up to 1500 untill the compressor got done cycling and it droped back down to where it should have been and didn't do it again the rest of the day. Just recharged the system a week ago and it's blowing nice and cold.

There is a ckt in there that ups the rpms when the compressor is engaged, always been that way with A/C, supposed to make up for the load of the running compressor.

RichP said:

There is a ckt in there that ups the rpms when the compressor is engaged, always been that way with A/C, supposed to make up for the load of the running compressor.

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thats what i was going ot say too.... i would try having that tested..... either that or have your compressor checked out

What is a ckt? I was looking in the FSM but don't know exactly what I am looking for.

:repair:

ericz said:

What is a ckt? I was looking in the FSM but don't know exactly what I am looking for.

:repair:

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circuit, just an abv for it. There is a control that has historically increased idle, back years ago it was a solenoid, now I think it comes from the computer. Might be labeled 'throttle advance' or something like that...

First off I have a 1998 XJ w/ 91,000 miles, 4.0, AX-15 and I have added a firepower ignition kit w/ plugs gaped to 60, 62mm TB, and snorkel ....Jeep was running fine at idle(750rpm) before I added the before mentioned and since I have added the goodies the idle will go from 750 to 1200rpm's(bounces) at standstill and when I am driving down the road at say for example 60mph at 2200rpm and come up on a light I will throw it out of gear and coast to the light about two blocks back or so and the rpm's will drop fast to 1500rpm's and stay there untill I come to a complete stop...meaning if I am rolling even at 2mph the rpm will be at 1500 untill I am finally at a standstill then drop to 1000rpm(and no my foot isnt even close to the gas pedal) and would like to know where to start on replacing and checking to narrow this down as all the sensors get expensive if ya buy two or three at a time and still no fixie....but I have checked all the vacuum lines that I saw and made sure they were snugged down and pulled the sensors off the TB and looked to see if they were clean and a good connection....looked in the haynes but for high idle it said 1.sticking throttle linkage(it isnt-checked it),2.choke not opened excessively-dont have one,3.idle speed incorrect,4.valve clearance on a V6-nope have an I6...Thanks for any info you all can give me it is greatly appreciated!!!!

Did you have the TB bored out ? was the job done and a smooth finish, I just wonder if the butterfly is sticking and not closing as far as it should.
I'm also not a fan of the aftermarket ignition stuff. Too many have had too many problems with them over the years.

RichP said:

Did you have the TB bored out ? was the job done and a smooth finish, I just wonder if the butterfly is sticking and not closing as far as it should.

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Its actually a brand new RE TB and was put on about a month ago!

EZridaz said:

Its actually a brand new RE TB and was put on about a month ago!

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I'd look it over and make sure you did not get a monday morning one...

RichP said:

I'm also not a fan of the aftermarket ignition stuff. Too many have had too many problems with them over the years.

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I actually had a problem with their Screamin Demon coil and sent it back.....after I installed the cap,rotor,plugs,wires and coil the XJ would hardly start and had to give it gas to keep it running so I put the factory coil back in and she ran fine with no probs....reset the computer after each attempt to make sure it was reading it right...by Monday morning do you mean a POS that slipped away from the assembly line?....TIA

EZridaz said:

I actually had a problem with their Screamin Demon coil and sent it back.....after I installed the cap,rotor,plugs,wires and coil the XJ would hardly start and had to give it gas to keep it running so I put the factory coil back in and she ran fine with no probs....reset the computer after each attempt to make sure it was reading it right...by Monday morning do you mean a POS that slipped away from the assembly line?....TIA

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Yup....

Concerning my bored TB, It does wistle a bit during acceleration. I'll take a closer look at it too.
I think I will clean the stock one and stick it back on tonight.

Now see, my TB is stock. Perhaps it just needs to be cleaned out?

Keep in mind that the throttle body works by allowing in air and the throttle position sensor tells the puter where the skinny pedal is by how far the butterfly is open. If you have a bad seal between the TB and the intake manifold I think the idle will go up as you are letting in more air and may be confusing the puter with inaccurate imputs from the throttle positon sensor and the mass air flow sensor. I'd check and see if you have a good seal. Quick way is to spray some 'mist' [water, wd40, etc] around the base of the throttle body. If the idle changes that where the air is leaking in from. It's also a good way to find other vacumn leaks. Could also be the bolts/nuts on the TB have worked loose.

That actually makes sense...lol. But why ONLY with the a/c on? Is it cause the engine is having to work a tad harder to run the compressor as well?

What would the torque specs be on the TB mounting nuts?.....about 20 or so?TIA