I am having some issues with my 94 z28. it was sitting for a long time while i was in Iraq but driven occasionally by my father. It starts very rough. any help or thoughts? there is also a slight knocking from the engine I'm assuming pistons. When i am able to drive it it is super sluggish all the way up to 3k rpm then seems to run fine but still rough. i changed spark plugs and check all cable connections but it still is having issues and i don't want to take it to a shop if its something i can fix myself. please help

Was it running bad before the spark plugs? had your dad commented on it when he was driving her? I posted in the other thread you mentioned this in. GM loved hard lines that got brittle with age and heat. Some of these pull vacuum, so if one had broke or come loose it would give strange running issues.

Was it running bad before the spark plugs? had your dad commented on it when he was driving her? I posted in the other thread you mentioned this in. GM loved hard lines that got brittle with age and heat. Some of these pull vacuum, so if one had broke or come loose it would give strange running issues.

yes it was running bad before the spark plugs, thats why i changed them, it ran like it was maybe not running on all cilinders, so i did the quick easy common sense fix. It did not start running bad until after i drove it for a month or so after i got back from iraq. I didnt do anythign out of the ordinary to cause it.

What lines are you talking about that pull the vacuum? where can i look for these?

Off the intake there will most likely be lines running to it. I'm not absolutley sure wherer they all would be.

This is an LT1 right? With optispark? Are you throwing any service angine lights or anything? I wonder if the gas skunked on you in that month you didn't drive it. Maybe some fuel system cleaner and a fresh tank of gas.

I was initially thinking vacuum because at lower engine speed the engine is making more vacuum. On an older 350 if you had a vacuum leak it would screw with your idle. I was thinking that it was sucking air from somewhere and the PCM was adjusting and raising the idle. As your get engine speed up the vacuum would decrease. Which would kind of make sense it ran better from 3K up, PCM stops ajusting from extra air coming in.

yes my service engine light is coming on. and yes it is an LT1 with omni spark i will check the lines off the intake, that sounds like the most logical explanation of what going wrong that i have heard form anybody, i will give it a shot and see what happens. thanks man ill report back after i check the lines.

Here is a pretty good link. You can do the paperclip test to get your codes. I think you have OBDI in that 94. They changed to OBDII in like 95.

http://tunertools.com/vendorinfo/OBDdiagnostics_page2.asp

Post your codes up and maybe we can get to the bottom of the issue.

Another think is the optispark. They are known to be a little flaky, yours might be going out on you. But pull the codes before buying parts.