bad stutter at 2000 rpm, only power key on

[Spanky1965]

hello all, newbe here, I am sure this has been covered but this car is driving me crazy.

Runs perfect under normal power, but turn on the power key and idle goes up, and at exactly 2000 rpm's at part or full throtle it sounds like it stutters, bad, clears up at 5500 and pulls hard to 7500.

I have changed the fuel filter and pumps. new plugs. From what I have read in other posts it sounds like bad injectors, but it realy feels like a carb with the choke sticking. I was wondering if the 2nd ports are not opening. I am in Springfield Missouri and need help

[Spanky1965]

just wanted to add the car sat for 3 years before i got it, it has 30,000 miles, and had the vacum line that runs to the comp on the drivers side disconected.

[tccrab]

Try this test:
Turn the Engine Power Key to off.
Run it hard, all the way up to 7000.
Turn the Engine Power Key to On.
Do the same thing.
You should notice a significant difference in power between the settings.
If there's only a slight difference or no difference at all, your secondaries system is suspect. Injectors, secondary actuators, secondary vacuum components will all cause symptoms like these. The fun part is figuring out which.

Here's everything you should ever need to know about your secondary port vacuum system:
http://www.corvetteactioncenter.com/...diagnosis.html

Good luck!

TomC
"Crabs"

[Spanky1965]

thanks Tom, the funny thing is there IS a big diff, not even close. also the vac pump runs for 3 sec and does not cycle on and off so i am assuming no vac leaks

[tccrab]

Originally Posted by Spanky1965

thanks Tom, the funny thing is there IS a big diff, not even close. also the vac pump runs for 3 sec and does not cycle on and off so i am assuming no vac leaks

Ok, so no huge vacuum leaks. That's good.
Narrows it down a tick.
Your secondary actuators could be sticking and then opening later than they should. That would cause a mid rpm bog as the fuel mixture goes rich and then once they're open, the power comes back as the mixture leans out.
It could be fuel injectors, if you've got secondary fuel injectors that aren't flowing like they should, it could cause a bog.
Coils can cause stumbling problems, check out this 3 year long horror story:
http://www.zr1netregistry.com/forum/...ead.php?t=1777
Doesn't sound like your problem though, my first guess would be fuel injectors, secondary actuators next.

TomC
"Crabs"

[Spanky1965]

I agree, but can you test the secondary actuators without removing the plenum?

[LGAFF]

Is the 2ndry MAP sensor under the ECM connected?

[Spanky1965]

yes it was diconected when I got it, but my friend did not drive it like you or I would, so not sure he even noticed. I have conected it

[tomtom72]

Originally Posted by Spanky1965

I agree, but can you test the secondary actuators without removing the plenum?

I'm not sure that this would work. The secondary actuators are twined and the line off of the left bank actuator is T-'ed to go to the 2* MAP sensor(under the ECM bracket). Maybe if you pull the line at the MAP and apply vacuum to it you might be able to watch the actuators' arms thru the gaps in the plenum runners.

I'm not sure if that will work.

[Kb7tif]

I bet your secondary throttle plates are not opening up or vacuum/injector problem. This stuff is generally easy to fix if you understand the system.
Here is a start.http://www.corvetteactioncenter.com/...diagnosis.html