I have a 1990 jeep laredo. My jeep is making an odd noise in the morning. It does it during warming up. It does not do it immediately it does it around 4 or 5 minutes after I start it. What it does is make a vacuum squeal it almost sounds like a balloon when you pinch the nozzle and let the air out slow. Then it starts to idle a bit fast. When it does this the brakes are a bit funky. Once it idles down it all goes away and the brakes are normal again. the noise sounded like it was coming around the egr valve and transducer. We thought it was the transducer We have replaced both, to no avail. We have checked the power brake booster. It's good. If anyone has any ideas I would really appreciate it.

 

Get a can of starting fluid and start spraying around sparingly while the engine is running cold. Remember to spray very carefully so you don't catch anything on fire. Hit all the vacuum fittings. The engine will rev up a little bit if you hit any leaks because the fluid will get sucked up into the system. Quick way to figure out whats going on.

 

i have the same noise on cold start up. i ignore it only because it seams to run great after warms up and noise goes away

 

minus the brake issue you are talking about, I had this same issue with my 1990 Laredo. It sounded like a whistling coming from the engine. As you stated too, it wouldn't happen initially, but when the engine came to temp (a few minutes later). Then my RPM's would rise. After much research and tinkering, I ended up finding that one of the bolts holding the intake manifold onto the engine block was waayyyy loose. It was the farthest back on upper portion of the manifold. After tightening it, there is no more high idle, no whistling, and no exhaust tick. She runs good now! I don't know if its the exact problem you have, but what your describing seems really close to what I just went through.

 

with the exception of the loss of brake booster vacuum, I was thinking the same things about the loose intake bolt around cylinder 5 and 6

 

As stated above, check intake manifold bolts before chasing anything else. With the engine cold, start snugging up the bolts working from the center out toward the ends.

 

The intake bolt ideas are pretty good but im pretty sure the loss of brakes at the same time is a pretty good indication that it is a vacuum problem...

 

Because of the high RPM's its definitely a vacuum leak dealing with the intake manifold somewhere. Whether the two problems just happen to come about at the same time or if they are connected I don't know. Just thought Id throw a suggestion to rule something out.

 

Intake bolts loosening up are a very common issue. Worth doing regardless, and just may fix it. More Jeeps get fixed with wrenches and hands than by making guesses on a computer.

 

We found 2 loose bolts on the manifold, thank you for the suggestion, glad to have that fixed and hopefully it will solve the problem. I'll have to wait for the next cold start.

 

Did you snug all of them up?

 

My husband snugged all on top, the noise is gone and my brakes work correctly now. Are there bolts underneath that he needs to do also?
Thank you so much for this advice it idles so much smoother. My jeep hasn't ran this quiet in along time

 

Ya, I would check the bolts holding the exhaust manifold on as well. With mine I had a loose bolt in the very back of the intake manifold and the lower back two bolts holding the exhaust manifold were loose as well. Now my idle is great.

 

The ones down below hold both intake and exhaust manifold on. Easiest to do after removing the air cleaner box.