My 91 Z28 idles fine, and when I first drive it, it runs with no problems for about a minute. After that, it has a terrible time accelerating. My first thought is the egr solenoid, but after looking at posts in the forums, the solenoid passes tests (blowing in the solenoid with car off and when doing a diagnostic test). Also, the egr valve appeared to hold vacuum - sucked air from vacuum line and the valve held 'vacuum'. The valve diaphragm also moves up and down freely. Additionally, the egr solenoid for my vehicle is no longer in production, so I used one from a 91 Caprice (VS18 instead of VS19). The only OEM solenoid I can find is on eBay and the seller wants almost $200.00 for a $50.00 part. Supply and demand! I have replaced the ignition coil, distributor cap, wires and plugs, IAC, TPS, MAP, ECM, Computer, and plenum and throttle body gaskets. I also can not find any vacuum leaks and I am not throwing any codes. The only non-stock items on the vehicle is FlowMaster exhaust, KandN air filter (attaches directly to the throttle body), and a stage 1 Gorilla chip. I thought perhaps the chip was faulty but I have the same problem with the chip installed or uninstalled. I have a new EGR solenoid on order but it won't be in for a few days. Any and all help from the forum will be greatly appreciated. There are some real brilliant individuals here.

Not sure about your problem.
But I clicked on your picture of your car and OMG!! Very nice!

Well there are alot of stupid little things that can cause this lets jsut start with a few easy ones. PCV valve? O2 Sensor? id also say vacuum leaks but u said it had none. I will keep thinking and check back.

Timing. BUT im gonna say you probably have an issue with your o2 sensor and your cars comp. I think whats happening is your prolly runing either a bit to lean or 2 rich so our o2 sensor is recognizing this and changing the injector pulse widths and then when you stand on it, it is possible its getting all confused and starts adjusting due to the increase in fuel and increased overlaped fuel from when the over lap of your cam has the intake and exhaust valve open and clean air fuel mixure flows thru your exhaust and the o2 sensor reads it and trys to compensate causing the retard in your acceleration.

Thank you for your response, sorry it has taken me a year to respond. A lot has changed since spring last year - wrecked the car, fixed it (waiting to paint it), found vacuum leak that was causing problem (line from vacuum canister to T that connects the canister, cruise control, and charcoal purge canister had a cut in it. Car ran like a dream after that. That is until I installed one of those cheap chips that connects to the pig-tail of the IAT (plenum temp). Well she started running like **** again, so took off chip, reset computer, and now I have the same damn problem all over again. I have replaced the O2 sensor, the EGR valve, checked the EGR solenoid, the MAP sensor, and ensured there were no vacuum leaks. Is it possible I damaged the computer? How would I know without purchasing a new one? She runs like a champ when she is first driven for the day, but once she gets into closed loop she sucks and can not accelerate for **** if I stomp on her. If I slowing accelerate she is not as bad but I can feel the bogging that is similar to the feeling of starting in second gear.