Got it running -- hesitates when cold

[VetteMed]

SO, after 3 months of working on it very intermittently, I fired up my '91 last night and drove it for the first time since I brought it home (bought it from an ebay seller in March).

When I drove it home initially, the secondaries were nonfunctional. During the course of changing the belt, the prior owner managed to damage the vacuum line running near the oil filter, as well as break the oil pressure sensor and oil temp sensor, rendering the secondaries inoperative. With the ignition on, the secondary vacuum pump ran continuously.

I pulled the plenum, installed new injectors from FIC, new GM coils, new wires, new plugs (gapped at 0.035). I removed the damaged section of vacuum line and spliced it back together.

SO, tonight I fired it up for the first time, once the rails primed it fired right up. The vacuum pump runs intermittently -- when it runs, it runs for only a second or two, then shuts off for an equal amount of time. This cycle repeates ad infinitum. The good news, is that the secondaries function -- WOW I still have some odds and ends to do, so I couldn't really enjoy it much, but it's definitely running better than when I brought it home.

However, during the first few minutes of driving, there's a bad hesitation/bogging from idle. It seemed to disappear when warmed up. As a side note, the car has a set of headers installed by a prior owner, no cats, and a chip from Z-Industries.

I ran around with my mityvac a little bit, and when I pull vacuum at the line from the pump to under the plenum, I can pull 10-15 mmHg but it drops approx 1mm/second thereafter. The same response is noted at the fitting on the driver's side between the intake runners, and the passenger side at the tube that runs from the coolant surge tank to under the plenum. When I pull vacuum on the tube between the runners on the passenger side, no drop in vacuum is observed. When I had the plenum off, the secondary actuators worked properly and held vacuum without dropping.

I know I still need to change the fuel filter, though I don't think that's a likely cause for a cold hesitation. Where should I look next?

Thanks!
Andrew