Still trying to figure this lumpy on cold start, runs ok after heat soak and hot start problem. Have learned to take OBD1 readings for a 22 second period. Have logged a few to spread sheet for analysis. Problem is I don't have a base line of what the OBD1 readings should be for a 1995 Z28 with no problems to compare to. If I knew what the norms are for cold start, warm up, and fully warmed up, it might point me to the real problem. I still suspect some sensors and/or the PCM. Any thoughts?
Thanks

 

Last post didn’t take.
Have been taking 22 second scans of car in both cold start and hot start operation. Been manually logging the scans into spreadsheets. Haven’t figured out how the direct link from scanner to pc is done of analysis purposes. Also, don’t know where to locate what a normal set of scans would look like, for purpose of comparison analysis. Need to get this cleared up. Planning to take a trip soon. Appreciate any help. Thanks

 

Scanning your LT1:

http://www.injuneer.com/ScanMast.html

 

Thanks for the link.
Have used it to analyze several OBD1 29 second scans. Done when cold started and hot started, right after started and driving on the road. In rough running after cold start and normal running after hot starts. Nothing from the PCM OBD1 data seem to indicate any variance from norms for cold or hot running. This problem just getting to be a real bear. Have also checked what might be suspect vacuum lines. Again nothing, not what it should be. The only thing you can depend on is rough running, like spark plugs missing, but no raw gas smell. After heat soak, it starts and runs normally. Don't know where to fo from here.

 

Z28 softtop ben, did you ever figure out your cold start rough idle and hot restart issues? I have been fighting this all summer and am experiencing the same issue you are - specifically that the car runs rough/crappy until it heat soaks and then runs good after that!