Chevrolet Repair: 1995 Chevy Astro Continued, fuel injection cleaner, chevy astro

Question
Hi Van. I asked you a question a few days ago about an idle problem with a 95 Astro. I wanted to give you some more info. we are still having the trouble. It is not a throttle body it is a plintom-not sure how to spell that.  We have put in fuel injection cleaner. The idle up and down only happens in park.  In drive the symptoms are the lundging forward even with the break on and the rough running and the sput and sputter.  You can actually feel the van move when it is sputtering bad.  We have taken the EGR Valve off and cleaned it  and no change at all.  My husband says he thinks he hears a vacuum leak on the drivers side when it is in park and the idle is coming back up from its dive.  But he can not locate it. And he is not sure if that would be normal because of the dramatic idling up and down. He said it sounds like it is dying for a breath as it dives done and you hear it gasping as it comes back up.  I know that probably sounds stupid, but this thing is driving up nuts.  It is a great running van except for this.  Sometimes it will idle up and down 5 times and stop, sometimes 20 and sometimes it just won't stop at all until you put it in drive. Even when we put the new throttle postition and o2 sensor on  no change.  Also when I turn on the defrost it almost kills it.  It has died on me before because I turn on the defrost. And if you are in park and you turn on the defrost it will start idling up and down really bad almost idles down so far it dies and then it pulls itself back up.  Then the next day you can start it turn the deforst on to warm up the van and it is fine!  AH AH AH. ha ha.  We are pulling out our hair.  I too want to say thank you for all your help and advice.  It is nice to have people like you who are willing to help out.  We appreciate it.  I hope my new information helps.  Again Thank you D

Answer
Hi D,
A vacuum leak could sure make it act like that, but I don't have a reason for it to leak only in park.

I would like to check the fuel pressure, and make sure it stays at the required pressure. I have seen vehicles with a hole in a hose INSIDE the fuel tank, where the pump connects to the fuel line. The pump ran fine, but when the pressure reached about 7 PSI, everything above that just squirted inside the tank. it would run jumpy, and no power. See if you can trace what sounds like a vacuum leak back to the tank. it could be that spraying you hear. But check the pressure if you can.

Another possible source for a vacuum leak is the brake booster. Does having your foot on the brakes seem to make any difference?

The defroster turns on the A/C compressor, which puts a pretty heavy load on the engine. Normal for it to do that, but if the engine is having problems, that extra load is just more than it can take.

Good luck,
Van