IAC Valve?

[Arnold]

the IDLE air control valve does NOTHING ABOVE idle.. other than act like a dash pot to prevent high manifold vacuum when you take your foot off the gas and close the throttle..

please verify the spark .. before you go anywhere else.. i have changed so many ignition coils on GM TBI and Vortec motors i cannot count them..

the sides of the coil will have marks like this grey area or worse on the sides
http://i.imgur.com/LIyPczv.jpg  this is where the high voltage spark leaks out ..no high voltage spark.. you won't have enough voltage to flash over the spark plug and rotor to cap gap and the engine will misfire or die...

how long does it take to check for spark..  a minute... how long does it take to change a coil on a  TBI or Vortec V8... under 15 minutes.. i did a vortec V6 coil in a 98 GMC safari in 12 minutes last week.  but i already had the engine cover off so that is kinda cheating.

how to tell.. use a spark gap tester.. 8 bucks.. at most parts stores.. not the neon bulb type.. the adjustable gap type.. if your coil looks like above.. don't bother . just replace it..  you can pull the coil wire out of the cap.. position it 1/2" from something metal and crank then engine.. if you only get a dull orange spark.. replace.. if you get a SNAPPY BRIGHT BLUE spark... then the coil may be OK.

a few things that will make your truck also just die..

bad ground connections.. there is a computer to engine ground connection for the TPS and some of the other sensors on either the thermostat stud or the stud directly behind the thermostat.  i have to replace that ring terminal the first time i work on so many TBI and Vortec engines another uncountable number..  

but the Computer MAIN ground is to the back of the cylinder heads...  where on a VAN you have to pull the engine cover, sorry..  there are a pair of wires that come out of the harness with ring terminals for this.


please examine the distributor cap.. the rotor.. man do those burn thru also.. the cap terminals burn up.  the center carbon also..  but before you throw anything back on.. grab your flash light.. aim it right down at the top of the reluctor..  that is the star shaped device on the distributor shaft.. the second layer is a ceramic magnet..  if its cracked.. you will need to change the distributor..
hopefully you will find a OEM brand.. not a delco.. and OEM or OER that is reman by A1 Cardone. they started using replacement distributor shafts on these with a solid reluctor.. no rivets.. no magnets to crack.. far superior AC wave form output..  i get them at Autozone.. i don't know who else carries them.  probably a lot..
the distributor cardone reman part number is.. 1995 Chevrolet Truck G30 1 ton Van 5.7L TBI 8cyl  Part Number: 30-1830  Alternate Part Number: DC804EFI

if the upper bushing is worn. the shaft will have side to side play.. where the pole pieces actually touch the pickup coil poles.. i have had them so bad it sounded like the valves were clicking..  up and down play is allowed ..

if you go to replace the distributor.. preset the engine please..  print this section out..   with your remote starter button hooked up and hopefully its one of the better ones that has a push button on the end..  place that in your hand upside down..  with it clenched in your fist..  bump your fist like you are playing rock paper scissors into something to push the button into that object.. floor board.. engine .. something solid. this will allow you to move the crank fractionally.. figure out where the number one wire is in the cap.. get the rotor almost pointing in that direction..  use tiny bumps to get the reluctor tip to align perfectly with the pickup coil poles..  if the rotor is pointing in the proper direction. and the poles are lined up .. if you go up front and look at the timing marks.. G Vans have a special timing pointer and additional mark usually..  that should be aligned at base timing.. what ever that is... 0TDC or 15 BTDC.  could be either.. i try not to remember the timing settings i always look them up. or check the emission label. i have a smog book that keeps getting put away that lists them...

back to the distributor..  if the pole pieces are aligned.. the rotor pointing in the proper direction . the crank marks should be at base timing..  you can now remove the distributor.  work on it.   use it like a baseball bat and swat rocks with it..  but when you install the new one.  you can actually drop it in.. you may have to use a long screw driver to reset the oil pump shaft.. but if you get it to seat..  you can turn the housing to align the pick up coil to the reluctor teeth.. lock the hold down plate and reassemble.  base timing will be so close its crazy..

i do that when i work on any distributor..  i can preset the engine/distributor.. pull the distributor.. work or change it.. put the new one in.. sometimes i use the remote starter button to spin the engine to get it to drop but only with the distributor in. so i know which crank turn i am on.. i bring the crank to base timing marks.. i turn the housing to align the pole pieces.. i lock the hold down plate.. reach thru the open window and start the engine without needing to turn the distributor..  this blows most people away.. they have never seen anything like that.

its just that with the crank set to base timing.. if the pole pieces are aligned and the rotor pointing to the number one wire.. the timing is going to be within 2 degrees.  its closer if you don't turn the crank backwards.. and you have to be on the #1 Compression stroke not the number six..

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next thing that can cause your issue.. CLOGGED CATS.. easy to tell.. unscrew the oxygen sensor.. unplug it..   start the engine.. rev it up..  what happens..  does it run good now.?? will it rev.. if so.. your cats may be clogged from the excess carbon from combustion or the crud from the seafoam treatments.

another thing.. bad MAP Sensor.  that domino shaped device with a green 3 wire plug. and a vacuum hose..  

you might also want to search out and just replace the engine coolant temp sensor and its pigtail.  at az.. its part number SU102.. from wells also the same number..  or an AC delco Part # : 213-52  that is both sensor and pigtail.. usually under 20 bucks for the pair..  either can go bad..  since you have a hard one to work on..

you may want to breeze thru this forum post i found.. http://forums.superchevy.com/corvette-fever/70/8585187/c4-corvettes/which-used-scan-tools-for-82-to-94-corvettes-with/   that guy knows scan tools.. who ever he is..

  That is a ton of great info Wayne

   This thing has lost the ability to produce enough cranking vacuum.I am highly suspecting it is just too carboned up. I thought it might have been a bad cam..(that would artificially raise it) and in combination with other leakage..leveled it out to normal
   Ya..one of the cylinders just leaks down like right now buids normal compression at a normal rate..at least it did when I checked it last.
   Could be that enough clean out stuff has softened enough carbon to allow the valves to seat..I doubt it.Maybe there is a burned seat.That is what used to happen. Deposits on usually the back face of the valve..working their way down..finally close to/on the seat. Then hot exhaust gases blowing by and burning the valve at the seat.
   I dunno..if I try it again..it is gonne have to have some cranking vacuum..before I go any further.

  The Iac..does/did quite a bit above an idle on this thing.   A couple of times after I had had it out and cleaned it..you could hear it hissing like crazy from quite  a a big vacuum leak..as the valve was stuck..then it moved toofar the other way I cannot see it as a problem now. It could not leak enough to lead to a no vacuum crank.
  When the iac was pretty freed up..that was the best it ran from idle up.

   I am lazy when it comes to GM hei units. Stick another one in
   I check them with a calibrated tester for Hei It is a little centre gap spark plug that has a clip attached to it. Stick plug lead in.Clip plug to metal. Spark. It has spark. I tested that already.I don't have an adjustable one. I found the adjustable ones good with points ignition..as head room seemed to be an issue. When hei came along..there was plenty of spark. I was stunned when I read what the likes of Jenkins did with just bone stock hei's. I used to have piles of them. I would get the curve info I needed/wanted..and could just get a particular " dist..or I could get the #'s for the weights and springs. Ditto for vac cans.
    The coolant sensor was next on my list.
    I don't think the cat was plugged..It seemed..to have plenty of power from above idle somewhat..and up..I mean that was only being revved up..not driven. Huge differences can occur there.
     I had a vacuum gauge on it when it died.I idled it down..and the vacuum just kept dropping..dropped below 8..now next to zero on cranking.
    Think I would rather replace the van than the heads on this one
    I already went through the vac system on this truck.

    Thanks Again