Squintz

**Update 3**
Fixed the issue by backing out the throttle body set screw. For some reason, the screw was set way too far out.
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**UPDATE 2**
Looks like all signs are pointing toward a vacuum leak. I started it up this morning. As it was warming up I started to pump the brakes, and the rpm's would quickly raise the more I pumped. Then, I changed the vents from face to defroster, and the RPM's shot up even more. I assume that the brakes and defroster would be running off vacuum? If so, do these symptoms sound like a vacuum leak?
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**UPDATE 1**
Capped off the hoses, replaced the TPS and IAC motor, and sprayed carb cleaner around the intake manifold (no change in idle), and still has a high idle.
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Hi everyone,

I'm new to the forum, and new to Jeeps. I picked up a 94 Jeep Grand Cherokee Laredo 4.0L I6 today as my new daily driver. Overall it's in excellent shape. Runs amazing and has 132K miles. I notice that it has a brand new radiator, and maybe some other parts, but everything is pretty much in great shape.

Just when I got it home, I noticed that it has a slightly high idle (1300 rpms). I did a quick search and found out that there isn't any way to directly adjust the idle, so I started looking around the engine for possible vacuum leaks. Sure enough, I notice some hoses around the air filter box that are not connected / broken. I really can't identify them, so I'm hoping the forum can help me find the right replacement parts. I'm also hoping that this is the culprit to the high idle.



This piece was attached to the air filter box, but the plastic hose was cracked just at the rubber connector (air filter box side). I took it off and noticed it had some sort of check valve attached to the end (which was also cracked). Red circle shows where it was cracked

Here is where it was connected to


This thin hose is connected to the intake manifold, and the other end was connected to the broken check valve device I pulled off in the last photos. It's not really a broken hose, but it may help identify that check valve device since it connects to it. Red circle shows where it's connected to the intake manifold




Sorry for all the photos, but I'm hoping someone can help me identify these hoses and what parts I may need to order to fix the high idle issue.

If these aren't causing the high idle, is there another way I can diagnose what may be causing it? The car runs great otherwise, no studdering or starting issues at all, and the engine is very quiet.

Thanks in advance

Timbone1343

I'm also new to jeeps and not too mechanically inclined however if it were me I'd just take it to the auto parts store and bring those parts in. Even if you don't buy them there because sometimes their prices are outrageous at least they can help identify them..

EDIT:
I'd also suggest trying to find a FSM and using that to help identify parts.

Squintz

Well, after some research, I believe that grey valve and the hoses connect to the Evap (vapor) canister.




I believe the hoses in questions are "I" and "L" from the lower diagram. Could this be effecting my idle? It's certainly causing a vacuum leak.

2Evil4U

Any vacuum leak can cause idle problems/lean conditions. At a minimum, plug them all off and see what happens. if it runs OK, doesn't throw any codes and gets reasonable gas mileage, I'd leave it.

Squintz

Well, I'd worry about the mileage with the idle like this. I replaced the TPS and IAC motor, and capped off the vacuum leaks, and still has a high idle.

I noticed that at cold startup, it's pretty normal around 1100rpm. But as it gets warmer, it starts creeping toward 1500 and stays there when hot.

highwater

Maybe check the map sensor it could be bad too mounted on firewall has one vacuum line running out of it . I had same prob ,but narrowed it down to tps . Thanks to the fellow xj guys on here . Awesome group of people

Squintz

Well, I tried unplugging the MAP sensor while the Jeep was running, and the idle stumbled and I got a CE light. So I don't know if it's bad. But I was thinking of trying the 02 sensor next.

Squintz

More updates.

Looks like all signs are pointing toward a vacuum leak. I started it up this morning. As it was warming up I started to pump the brakes, and the rpm's would quickly raise the more I pumped. Then, I changed the vents from face to defroster, and the RPM's shot up even more. I assume that the brakes and defroster would be running off vacuum? If so, do these symptoms sound like a vacuum leak?

Squintz

Tonight I replaced as many vacuum hoses as possible, and even secured many of them with zip ties. After doing this, I tried running the jeep again, but STILL had high idle. So I decided trying one more thing that I read on another forum. The FSM says not to adjust the factory set screw on the throttle body since idle is controlled by the computer. However, someone else with the exact same symptoms I have (idle gets higher as Jeep warms up) ended up taking off the throttle body and adjusting this screw. So, I removed the throttle body, took a look at the screw, and noticed that the screw had rust only about half way up the threaded part (almost as if it was farther in at some point). So I adjusted the screw so only the rusted part was showing, reinstalled the throttle body, and IT WORKED. Idle is now ~500rpm's when fully warmed up, and it runs great. No idea why, but the previous owner must have turned up the idle by adjusting this screw at some point.

2Evil4U

Fantastic. Good fix.

PO probably jacked the idle because with all the vacuum leaks it was so lean it wouldn't stay running.

Congrats!

highwater

Awesome man glad she is purring like a kitten