I noticed today that I had a vacuum leak, but what exactly would a vacuum leak do? I never noticed a problem with defrost like I hear everyone talk about with a vacuum leak. No cel light. There are two tubes (plastic) that looks like it comes inbetween the intake and valve cover (didnt look that close) and travels over towards the pcm where there is about a 2 in section of rubber hose (which looked fine from the front, but after putting my hand around it i can hear the difference. Took it off and noticed that the tube was completely cracked open in a few spots. Pretty much could have had no hose on there and had the same effect. With the engine running i put my thumb over the engine side tube inlet and the engine seemed to dip a little bit and then return to normal idle. then when you let go, its like you just tap'd the gas pedel a bit and she rev'd a little and leveled back out. I always have a cold idle startup problem where it would dip and rev and repeat3 times and she would be fine for the rest of the day. At idle with the old cracked hose, it sounded like "tisk tisk tisk" repeatledly. Now there is no sound. The one section of plastic hose travels from the engine to just about the pcm, then joined by the 2 in section of hose and then over to the left fender where the plastic tube bent about 90 degrees down to what I thought was the evap stuff. What kind of adverse effects would such a vacuume leak have on my truck. Also I seem to never get the cel light (not that im wishing too... ) but shouldnt it come on for that?

Thanks in advance,
pcfixerpro


---EDIT
01 1500 5.2

 

it could cause poor idle, stumbling on acceleration, pinging, cruise problems, 4wd CAD operation, htr/def controls... you should fix it.

 

darn! now that you mention it, that 4wd cad unit was messing up pretty bad the other day. I got stuck in levelgrass. Put it in 4wd and I swore that she never kicked in. I dont have cruise, and she runs great to be honest, just that wierd morning idle sometimes and never had a problem for kickdown or acceleration or pinging. Thanks!

 

I fixed that leak, but in the process she has developeda stumble at startup sometimes. Woo hoo! Sometime's she'll fire right up, other times... she will crank crank crank crank stumble stumble fire. or just stumble and fire. The crank crank crank one happened only one time. Just started doing it. No problems after the truck fires and drives fine. Just sometimes its a guessing game it seems. Fuel pump kicks in, and depends on what mood she's in if she wants to start or not. It has happend a few times today and... maybe its the gas, maybe its that vacuume leak, or... maybe its just something else to go wrong that I really don't need right now. I'll check my wires and everything tomarrow, reset pcm, and Run the gas down and give her some more, and.. yup go from there. Anything else or suggestions as to what would cause this problem? First time I've ever heard her do that.

 

sounds like IAC. see one of my recent threads. when you are not mashing the gas, the throttle plates are closed, and no air can pass,and the truck will not run or crank. the method that it uses to get air around the closed plates is via the idle port, which is controlled by the idle air control motor. it turns a pintle (plunger) to run it in/out and create a bigger/smaller hole at the idle port, to let in more/less air. its on the back side of the tb, and it has a noticable whistleing sound, which is normal.

when you start the truck w/o mashing the gas, the IAC runs the pintle out/in to position it to the right spot, and then its supposed to make very very minor adjustments to maintain idle speed in the 1000(cold) - 600 (warm) range. when the idle is surging up/down in wide ranges, its because the IAC is sending the pcm confusing signals, and the pcm keeps giving it in/out instructions.

when yours does the crank crank crank thing w/o starting, its likely the IAC is closed up. it will likely start up if you mash the gas slightly to open the trottle plate. also, if it won't idle, then again mash the gas slightly. the opening of the throttle plates bypasses the IAC.

they cost about 40-50 new. i'm on my third one in the last month. best to reset pcm when you change it. watch for warranty, and if they don't work perfect, get it out and swap it. they don't get better.