1991 Z-71 5.7l Tbi - Idle Surging Problem (at Cold)

[kombos]

I recently replaced the intake gaskets on this engine as it had a slow coolant leak. Once I got it all back together it idle surges when the motor is stone cold (~70 degs in Phoenix) after sitting all night. It takes a little more cranking than normal for it to start and then it surges between about 500 and 1500 rpm for about 10-15 secs, then settles to a decent idle. Still runs somewhat sluggish for the next 5-10 minutes, but then all runs fine after the engine is fully warm. In the afternoon it may surge a few seconds and have a little hesitation for a short while until warm.

 

I have tried waiting until the fuel pump times out and then cranking, but that makes no difference. There also seems to be no high speed fuel starvation so I think the fuel pump is fine.

 

I'm thinking I affected something when I changed the intake gaskets. I did have to pull the distributor and a lot of sensors/connectors.

 

The EGR was completely carbon plugged and I cleaned that out. I thought the EGR might be opening when it shouldn't so I currently have a plate over it, blocking it while I try to figure this out.

 

I am confident the new TBI gasket I installed is sealing good and I don't think this quite matches the gasket leak problem (I've seen before on these engines).

 

Was throwing no codes until I went on a long (70 miles) highway trip and it threw up a 44 (lean) code......but is now off again.

 

Hooked up a SnapOn scanner and it seems the IAC counts look fairly steady during the surging and the MAP looks fairly steady. TPS at idle is 0.62V. Coolant temp reads fine, and I replaced the sensor with no change in behavior.

 

Could this be some type of intake leak (I fear)?

 

Does the O2 sensor play any part at this time after startup?

 

Could I have a damaged ignition module?

 

Other ideas?

 

Appreciate any and all input.

Jay