Ok y'all, I'm looking for a few opinions here. I have a 1998 4.2L with about 170k on it. About a week ago it started throwing P0171, P0174, P0420 DTCs and an obvious vac leak. I found a vacuum leak problem with the PCV (big surprise!) and I replaced the valve and elbow and its running better now but it still has a rough (nearly stalls) idle, tends to 'surge' at idle and low speeds and there is still that PITA high whistling sound. I cleaned the MAF (which seems to have helped). I think the vac leak is coming from the EGR valve or possibly the IAC. I used some carb cleaner to check if the idle changes when sprayed but they are so close to each other it's hard to tell which one is sucking the spray in... Any ideas?

 

If you sprayed carb cleaner anywhere close to the EGR valve, you need a new one. Never use carb cleaner for anything other than what it's for. You'll blow the diaphragm in the EGR valve for one and two, carb cleaner eats rubber/plastic, gaskets, just about anything less than metal. If the EGR got hit, it's fried. Suck test it , you'll see.

You may need all new gaskets at this point, from the manifold up. Check the emissions harness anything that may have been compromised w/carb cleaner.

Never use that stuff, just a mist of it will eat away the plunger rubbers in the IAC.

 

Thanks for the reply jbrew... looks like I know what my weekend looks like now...

 

Yea, that's bad stuff.

The 420 DTC is isolated, -different problem. That's indicating an exhaust leak, like a cracked cat. They like to crack across the bottom , under the heat shield. Or, your converter is shot. It's not the O2's.

 

Ok, I replaced the EGR valve but I still hear a hissing sound that sounds like its coming from the middle/back of the engine. Maybe intake manifold gaskets or exhaust manifold? I did replace the vac line from the PCV to the back of the intake because it looked like crap. I don't see anything wrong with the elbow and it doesn't sound like the PCV is whistling, although I am going to replace it tomorrow. Any ideas?

 

Replace the elbow.

 

Ok, next stupid question. I have seen postings that say the PCV valve is in the valve cover (where I would expect it to be), some say its in the back of the manifold riser, and some say at the base of the throttle body near the air intake. This is a 98 4.2L 2WD... when I look at the part at AZ.com, they show several different valves for my year. I found what I thought was the PCV, in a grommet on the valve cover, but its "T" shaped and has a line running to the back of the intake riser and another running to the base of the air intake by the IAC... WTHeck?

 

yup, that's it. the PCV valve is the piece you've found in the valve cover. it will have two lines coming from it. one will go into the back of the manifold...and the other will run underneath the manifold into the elbow under the throttle body. so, the PCV valve is in the back (check for holes in the hoses that connect to it) and the "elbow" everyone talks about is under the throttle body. it is a 90 degree rubber hose that is notorious for getting holes.

 

intake manifold runner control diaphragm on the back of the block

 

You reopened a thread that's been dead for 3 years to post that?

 

To be fair there isn't many choices when you Google these trucks