1983 Z28 LG4. Only mod is an open air element w/ K&N filter. CC Quadrajet on top. If I hold the throttle open partially while driving, lets say at 35 or 40 mph and it stays at that position for more than 45 seconds, the car will feel like it cuts out, then comes back. If you hit the throttle during this cut out, it snaps right back to life and accelerates. I have a 12 mile drive to work that takes about 30 minutes to complete. At about the 12-15 minute mark, it stops doing this completely.

The car starts fine and idles fine for the most part. Sometimes at stop lights it will idle at 500rpms and kind of rough, but 9 times out of 10 its right at 750 and smooth. Any ideas?

Im running 89 octane if it matters.

 

Reading your post makes me think of EGR. Can you try checking your vacuum while its doing the surging? Or just check all of your vacuum lines. Maybe the EGR isn't fully closing or something. They're both easy things to just check.

Then if still no dice, see if the car is going into closed loop. I.e. checking for varying dwell when its warmed up.

 

I will have to figure out how to check the EGR and the dwell. I have very limited tools and nothing I own is auto specific. I do have a Haynes Manual so I will consult that. Hopefully it's something I can diagnose wihtout any specialty tools.

 

Doing a little more reading in other threads and found this...
https://www.thirdgen.org/forums/tech...open-loop.html

Sounds very similar to my issue. My temp guage never reads higher than 170*F All my other cars would climb up to 210 or so. Even in stop and go traffic in Florida sun, it's at 170*. For about 3 weeks, it spiked itself into the straosphere at startup and stuck there, reading 350+ straight up verticle... no matter if the key was on or off. It suddenly "corrected" itself and reads normally now. Think the temp sensor is bad and thats throwing everything off for open loop operation?

 

If you have access to a scan tool like Auto Xray, you can see what the CTS is telling the computer. The gauge gets its signal from a temp sender, not the CTS, so it's possible for the two to read differently. But, they should read the same.