Idle surging / vacuum

[pipesndrums]

Hi guys, bought my first Jeep Wrangler this week after many years of wanting one and super excited to own one now. 2005 Jeep Wrangler X 4.0.

Previous owner said that the AC was blowing only through the defrost vent and said it would need a part and the dash removed. Got it home and confirmed yup only defrost blowing. Checked this forum and looked for vacuum leaks and found the vacuum was disconnected completely! Whaaat. Had a cable tie on it so thinking maybe damaged but I plugged that back in and now AC blower was blowing out the front vents.

But... later i was out driving around and noticed it was surging at idle, with the brake on it was revving up and down, which so unnerved the guy in front of me at the stoplight so much he started to edge away. jeep was acting like a Monster Truck getting ready to roll over him. Sorry dude its not me, my engine is possessed! So after I got home, disconnected from the port again and now no surging but also back to defrost only AC.

Has anyone in the group experienced that too? Wondering where to start troubleshooting. Thanks!

 

[Jerry Bransford]

That it happens only while the brakes are on makes me think it could be related to the vacuum-powered power brake booster. The booster is connected via a larger diameter vacuum hose to the intake manifold to get its vacuum from to power the booster. I'd be tempted to temporarily plug that vacuum hose which would disable the power brake booster, and see if you still get the surging idle during a careful drive around your neighborhood, minding that while your brakes would still work, the power brake function wouldn't be there so you'd have to step down considerably harder on the brake pedal.

By the way I'm big fan of pipe & drum bands and love going to our local (big!) Scottish Games held annually near by. None of my friends or family want to go again though, bagpipes aren't for them.

 

[pipesndrums]

Hi Jerry, thanks for the update. I have noticed the brakes seem a little soft but I was assuming that might be normal. Will check that out. Now that the vacuum line is disconnected again and just hanging loose, no surging. I can try plugging it to see what that does too.

Yes same here on pipes and drums, big fan and I have played some competitions here in TX. Maybe see you at a Games some day!

 

[CharlesHS]

Sounds like a substantial vacuum leak in the vacuum line coming from the engine supplying the climate controls. Trace the line thru the firewall, there is a T which goes to the vacuum accumulator tank beneath the battery, the other line goes across the back of the engine and connects to the intake manifold. Then there is another T where it ties into the intake manifold that goes to the cruise control actuator. You will need to determine where the leak is in these lines.
Check the lines from the intake manifold out towards the A/C, cruise and accumulator.

 

[pipesndrums]

Thanks Charles, will do!

 

[Lowcountryearl]

Was there an end result to this?

 

[pipesndrums]

Not so far but still working on it. Vacuum hose on the manifold keeps popping off. Will get that fixed then trace it around. Seems like under the battery is another possible vacuum leak location. Will update when I have more details.

 

[pipesndrums]

Not so far but still working on it. Vacuum hose on the manifold keeps popping off. Will get that fixed then trace it around. Seems like under the battery is another possible vacuum leak location. Will update when I have more details.

Forgot to post an update on this one and close it out. Replaced the vacuum line, connected it in all the right places and all is well. Never did find the leak but a new line worked like a charm. Good to go. Thanks everyone for your suggestions!