Lacking a better word for it, my 91 corvette has started surging. When idling it will surge up to about 1500 rpm then drop back down to normal. Sometimes it drops down to the point that it will die and have to be restarted. When driving up to about 35-40 miles an hour it will surge about 5 mph then drop back. After driving it hard it will idle and run fine for about 5-10 minutes then start it again. The fuel injectors and fuel pressure regulator are less than a year old, although anything is possible, I don't think it is them. Any ideas what might be causing this. As always I appreciate all the help I get from all you guys and gals.

 

Look for bad vacumme lines and clean your throttle body.

 

I had this issue several years ago when I installed the ZZ4 into my 85. Drove me up a wall. Just could not figure it out. I had no vacuum leaks. Fuel pressure was good. Finally took it to a shop and they discovered that a injector electrical fitting was bad and worked on and off. So what was happening is it would dump fuel at one point..the O2 sensor would read a rich condition and shorten the injector pulse. The O2 would then read a lean condition and add fuel...Bottom line was it would add and subract resulting in the idle swing. It would go swing in 100-150 RPM increments ever increasing and decreasing. Finally it would hit 400 RPM and die.

You could try removing the clip off of one injector as it idles. It might run a little rough, but if your idle swing stops you have found the issue.

 

Does indicate a connection with the Oxy sensor. Have you tested the Oxy Sensors voltage output before and while this event is happening ? Alos the same for the fuel pressure at the fuel rail ??

I had a similar issue, and after we installed a new ZZ4 crate engine, etc. I had a friend who was an electronic engineer at Bowling Green, we met at a engineer week long seminar. I told him re my crazy idle and rough running engine. He knew the ZZ4 engine quite well, and gave me the part numbers for larger Bosch Injectors, a larger Throttle Body and a 3 wire Oxy Sensor, but with new wiring feeds, per his drawing.

Car ran great for a few days and then, The engine would get up to Temp and she runs like #$&&. I was pretty peeved, new engine, new Doug Nash trans, new Diffy with 3:73 gears, rebuilt half shafts, new oem seat covers carpet,,, and my SMOG test was a few days away.

So I figured that I could get the car to the SMOG test station before any engine issues. So when I popped the hood and did a visual check before leaving I noticed the BBK name embossed into the plate on the top of the Throttle Body. I decided to replace with the original GM plate. Low & Behold there are air passage was under this plate and the Gasket was missing. I cut out a gasket install it and she passed.

I had a few other electrical engine ECM & wiring issues. I'm considering a ECM & wiring swap.

Good Luck

 

Check that all cylinders are operating, my surging was caused by a bad #8 injector plug. Took 2 months to find it.