WhiteZ28

i have this '94 z28 with the LT-1/auto and for the first year it ran great with no issues but just in the last few weeks its ben having a few problems and today it got really bad. The wierd thing is that it runs fine half of the time but the other half it gives me a bunch of crap.

1)very rough idle and it shakes and it stalls out.

2)when its idling rough and i try to revv it, it backfires and shakes.

3)this one just happened today for the first time. after multiple attempts to start it and getting the rough idle it was finally running somewhat smooth. i noticed while going through my work parking lot that even though my foot was not touching the gas the car was pulling me along at about 15mph. then i turned onto the street and went to accelerate and when i got to high rpms they wouldnt drop, like the throttle was stuck, so i stopped in the middle of the road and put it in park and the car redlined like i was flooring it even though i wasnt touching the gas. so i turned the car off and after multiple attempts to start it was running VERY bad but it got me into a parking lot, and i tried starting it 3 times and it just kept revving up so i turned it off. then after 2 hours i started it and it seemed fine so i drove it home.

i really want to get this stuff sorted out so any information is helpful. thanks in advance.

P.S. i was told when i got the car that the engine is not original but was taken out of a '94 impala SS

suzuki-guy

any check engine light?

WhiteZ28

No, but i dont think its hooked up really. i haven had a chance to get a scan on it yet either.

NOVAZ27

Check the OPTISPARK, EGR VALVE, IN LINE FUEL FILTER. The Caprice/Impalas had an in line fuel filter on the chassis frame under the driverside rear passenger seat. The Z28 may have a similar filter in a similar location. The EGR valves on the LT1 & 4.3 V8s were known to be weak causing hesitation/ stumbling. They run about $60 at AZ. OPTISPARK are a great dist. but do not let them get excess moisture inside. I am sure there are threads that address these items posted here on the forum.

HOPE THIS HELPS

WhiteZ28

yeah the main thing ive been hearing alot about is the optispark. the other 2 things i was told was that it could be the the throttle position sensor and the fact that my cat is gutted?? but that doesnt sound right

WhiteZ28

also, the guy i got the car from said the motor was not original but is an iron head Lt1 from a 94 impala SS, if i was going to buy a optispark for it, are they universal for the 93'-'94 Lt1's or should i buy one specifically advertised for a Impala SS????

NOVAZ27

There are two styles for the optispark. One cap is vented and one is not. This is for the afore mentioned moisture problem. Check to see what you have on your engine. I think??? they will physically interchange. You realize that the water pump has to be removed to change out the optispark cap & rotor. PIA. I would checkout everything else first, EGR, FUEL FILTER, sensors, ETC. first. Simple to the hardest.

HOPE THIS HELPS

WhiteZ28

thanks for the reply. isnt the vented opti only on the 95 and ups? and youre right i would rather do the smaller, cheaper things first then if the problems persist ill do the opti.