I have searched several forums including this one and I haven't found the exact symptoms I am experiencing. Here's the deal. When my tuck is cold with the heat/defrost/etc. turned on the engine stumbles at idle. When the gas peddle is pushed it idles erratically but once it is up to speed there is no longer a stumble. I'm not experiencing any power loss, etc. Just wondering what this stumble is?

I have some ideas, abut I want to see what you all think first.

Thanks!

 

You have a vacuum leak. If it's doing it when the defrost is on, which is vacuum operated you could have a broken hose or a bad check valve that goes to the HVAC head. That's my idea. At idle it will be very noticeable but driving you won't notice it.

 

John, thanks for the help. Where should I start and what should I look for? Thanks! Also I just recently put SeaFoam in the brake booster could I have made the vacuum leak from there?

Thanks again.

 

Cory, you might want to check your connection from the brake master cylinder to your intake manifold where you sucked in the seafoam. thats most likely where your leak is. if this isnt the case you can use a can of carbeuretor or throttle body cleaner and spray around your intake, master cylinder and all other vacuum hose connections while the truck is running and idling erratically. if at any point in time while spraying different areas you hear a jump in idle rpm above the norm... you've found your leak. isolate and repair as necessary.

 

Andrew, thanks for the help. I will do that. Does anyone know a way to find a route diagram in which the vacuum system works on my truck? is it in the Clymer or Haynes manuals somewhere? Is this the same vacuum system that runs the 4X4 hubs?

 

no problem bro. should be able to find it in the haynes manual. and yes, it is one and the same that engages your hubs sir.

 

So if the vacuum on my 4X4 system doesn't work, then the leak could be from there? Or is it too far from the engine to make the idle erratic? It would suck to have to fix this, even though I don't use it to make my engine stop stumbling. But if that is what I have to do, then....
Also I have a bit of a leak in my exhaust just before the muffler, could this hinder the problem?

 

The vacuum lines for the 4wd could be the problem. I say get rid of them and plug the ports then get manual hubs when you have so money. An exhaust leak at the muffler wouldn't do anything.

 

Yeah, I have been planning on getting rid of the vacuum system on the 4wd and blocking them off. I just need the dough. I didn't think the exhaust leak would do anything (but maybe give me bad gas mileage). So I guess I start searching the vacuum system tomorrow. I don't really know where to start but I will get my Haynes out tonight and have a looksy.

 

Check the vacuum ball on the passenger side for any cracks or broken ports.