3.4 DOHC strange running

[johnsgarage99]

Excellent site, i need input on my 96 Monte 3.4 DOHC

Heres the scoop:
hard starting-cold- usually starts on 3-4 try
first 5 minutes the idle is all over 1,100-3000 rpm
then it runs normal
but hard to start if out running errands- engine at normal operating temp


i got this car as a basketcase, i have since
replaced the following:
catalytic convertor- none on car now
installed autolite single plat plugs
replaced most the vacuum lines/hoses
pcv valve
upper intake gaskets
map sensor
coolant temp level indicator-in radiator
coolant temp sensor in lower intake(gm engineer asleep on that design...!!)
fuel filter-twice(thinking i had garbage in fuel system)

the only codes set where - map sensor high voltage,
map sensor performance

if you take for a test drive,she runs great above idle, gets out and
moves,but the crazy idling has me stumped--or i overlooked something
way simple.

any ideas ....?????

[jmgtp]

Sounds a lot like a vacuum leak. I saw mention of replacing the upper intake gasket but you may want to consider the lowers as well. If you have a 96+ don't forget about the plenum to throttle arm and throttlebody gaskets as well. If it runs normal once it warms up that can be indicative that once the metal expands from the heat the manifolds are making a vacuum tight seal against one another. I'd start by replacing the lower intake gaskets, they are prone to failure.

[johnsgarage99]

Idle relearn for OB2

thanks for the reply:
i did check for vacuum leaks ,using a can of starting fluid, and it showed the upper intake.
after taking it apart i saw that previously someone had it apart, and had incorrectly reassembled(incorrect bolts ). i check for vacum leaks now and nothing.
what concerns me is that high voltage to the MAP sensor. i replaced it once and wonder
if the high voltage to it, has blown it out again. i believe it is suppose to be 5 volts to it.
what is causing it to be more than 5 volts..????

Does the 96 need to have a IDLE relearn...????

[SappySE107]

How is it over 5 volts? You have a ground, reference 5 volt, and actual map voltage. Check your grounds and check the 5 volt reference on the TPS as well.

I too think its the lower intake gaskets. Usualy symptoms of a gasket leak. MAP sensor voltage won't be right either with a leak.

[z34phoenix]

my money is on a vac leak aswell... the bouncing idle is a dead givaway to a vac leak. lol 90% of all runing issues or starting issues are due to vac leaks on this motor! well prob not 90% but it is the root cause of most issues.

while under there you might want to check the oil drive shaft oring... and make sure its not leaking. its another common issue with the dohc.