Vacuum Help Please

I recently replaced the valve cover gasket on my 97 4.0L and now have several problems with engine.

First off, upon a cold start, the engine idles high-above 1k and eventually idles down to 750 within 30 secs or so.

Secondly, when the engine is ideling switching from let's say heat through floor-vents to mid-vents happens almost instantly, but when driving, if my foot is on the accelerator, the heat won't switch until after I take foot off of the accelerator.

Could this be a CCV problem? I do have some oil leaking from the rear valve grommet, going to replace this soon as I get the parts in-heard it was a B!t$h.

A frind of mine said that this ultimately sounded like a vacuum line problem and everywhere over the net ppl have same diagnosis for similar symptoms, however, I have no idea where to start. I have bought a Chiltons and am ready to solve the problem I just need a little direction. Thanks in advance for your
time everyone!

I just had the high idle problem at start up.... Turned out the injector o-rings were leaking. Spray some carb cleaner around the injectors while it's running. and see if the idle changes ..... Keep a fire extinguisher handy....

I have the same issue on my 88 Wagoneer also heater and ac it like shuts down until I let off the skinny pedal then kicks back in eager to see if anyone has a idea about it

check behind the pass. side of the front bumper for a vacuum "ball"-- it is vacuum supply for the HVAC system.

if it's there, follow the lines attached to it back to the engine looking for a break in the lines. They usually break under/behind the battery tray.

A slightly "high" idle that drops to 750 is normal operation. The HVAC not shifting unless the throttle is shut is not. You have a vacuum leak. Do you have a vacuum gauge? If not, go pop for one at your local parts house as you are going to need it to find the leak... If you are in the Springs, you are welcome to come over and I will help you find the leak. PM if interested.

An interesting fun fact. When I was chacing my low vacuum issue (Cruise Control) I wound up coating the vacuum reservoir in epoxy and fibreglass. Picked up nearly 2"Hg at the CC Servo. It must have had microcracks in it. During the cure phase of the resin, I pumped the reservoir down (put it under vacuum) until the resin was no longer tacky.

Not saying this is the problem. In fact, this was the first time it was not just a chafe through in one of the hard lines of the system.

Mud_Butt-Sounds a little dangerous, but everything is worth a try. Prolly just clean around while engine is not so hot. Valve cover and manifold need a good scrub anyways after I get CCV elbow installed.

Shorty-I inspected ball yesterday. With the engine shut off I pulled the line and got a brief hissing noise. With the engine running I pulled the line and got suction. I will trace line back today. Should have done that yesterday but I figured since I had suction there wasn't a problem with line. Also, is there a way to check for leaks with liquid cleaners? Maybe spraying and looking for bubbles/reaction, IDK just an idea, has anyone done this before?

Well off to get some parts and a Rad flush kit-she needs it-I need it. Can't beat good beer/cigars/and working on/spending time with our loved ones!

I'll get back with an update to let y'all know this afternoon. Thanks guys!

It was the Vacuum. I linked up with O-Guage and we solved the problem in 5 min. First we started at the manifold and got a "stock" reading off of it and found that the reservoir and it's line were running about 3 in Hg less than at the manifold. So, we put some sealant on and around elbow running into round reservoir and also put a new length of line running into the manifold after the check valve.
Problem solved, heat switches from defrost to floor to vents even when I've got my foot on the accelerator. Thanks everyone! Now on to the CCV valves and their grommets.

:cheers: