low vacuum

[stephen p luce]

I have a 89 K1500 vortec 350 TBI 15 lb f/p spring 46mm throttle body timing at 0 ecm flashed. I can't get it to idle less than 1000 rpm have done idle reset no help. the real problem I have is after I run it and it's up to temp and turn it off and start it after about an hour the manifold vacuum is at 14" and the MAP voltage goes up to 1.8v and it hardly runs then in about minute or so the vacuum goes back up to 18" and smooths out. I'v plugged all the vac ports on the TBI unit, no help. all the data on my scanner looks to be ok. Anybody have any ideas as where to look next, Intake gaskets? engine has been together for about 18 months, egr is not getting a signal when this happens.
It has the vortec to TBI intake on it, can't think of any other info that might be helpful.
Thanks for any help with this problem.

 

[Frank Enstein]

Check the coolant temp sensor. If it thinks the engine is colder than is really is it could be adding extra fuel it doesn't need. Maybe add some timing at idle. The 0 degrees is the initial timing but as soon as it starts the computer will add advance. Make sure it isn't staying @ 0 degrees after it starts. This might also allow a lower idle speed.