I have a 94 Z28 that is missing out rather bad at "times"
From the time I start it till about after 10 minutes of driveing it misses out like mad, feels like your shutting off the engine and cutting it back on. But then it clears up and drives like a champ. Everynow and then if driveing for a long period of time I.E just all around town makeing stops here and there, it will start to miss again then clear up again.
Everyone I have talked to seems to think its the optispark.
One thing that made me nervous was i drove it night for the first time since it started doing this and I noticed that when the car would miss the lights would dimm.

Has anyone else noticed this happening when their optispark went out or started going out on them?

 

most common problem would be opti, whats the tune up history of it? year? last opti replacement? have you checked to see if the water pump is leaking?

 

only thing that has been done is the plugs and wires have been changed, never changed the opti befor, never had a engine problem befor now, as far as I can tell the water pump is not leaking, that dont mean its not for sure.
I'm just scared of spending the money and it end up being something else.

 

your best bet is the opti...go ahead and get it changed anyway if you have a good bit of miles on the car. if you are good with doing work yourself, and have time, then change it yourself. some places around here want about $400-$500 to do it, and that's just labor charges

 

how many kms on the opti? for the water pump you can check under the pump to see if its wet by the weep hole. also if your coolant is down a bit. sounds like a opti to me. mine did what you describe.

 

yeah its up at 93K miles now. Just hate to dump the money into this thing right befor X-mas. And yeah I'll be doing the work myself. the places around here seem to hate my car, everyone wants a 1k to do the work, and that too is just labor.
The cheapest i have found the opti for is 325.
i come accross what sounds like a great deal at first then i find out its only the inside piece.
guess i'll keep shoping

 

Something else I forgot to mention.
if I let the car sit at Ilde it will actually rev up to about 2k rpm and then back down and goes back and forth.
First time it did that it was cold outside and I was letting the car warmed up while i brushed my teeth, i went running outside cause I thought someone was trying to steal it.

 

for the opti you can find for about 225 from jason or dal, do a search.

for the rough idling it could be the IAC.

 

Does it miss while driving or only at idle? Jason Cromer sells them at a good price...

 

it Does'nt miss at Idle at all, Only while under a load.
I can sit in neutral and rev it all day long and it wont miss a beat, put it in gear and go down the road and be ready for a sore neck.

 

I'm not convinced its your opti.

Voltage regulation problem? Fuel injected cars need a consistent voltage source.

To me it sounds like something else because it is alternating between working and not working. Not a problem all the time, or a problem just when its hot or just when it's cold.

I've never heard of the opti causing the revving phenomenon you describe. Maybe check for a torn intake or something that would be letting in unmetered air.

Opti often causes problems at a specific rpm(typically higher), although it can cause it over a range of rpms.

I would say replace your coil because you didn't list that with the plug and wires, but in my experience that is usually more a hot problem.

I'm sorry that I don't have the magical power to tell you x part. I just don't think that the opti is going to fix it for you from what you described. I could easily be wrong, but it's an expensive part to go replacing if your not sure.

IMHO the opti doesn't quite deserve all the notariety it recieves.

-brent

 

Another possibility is the Ignition Control Module. It could be getting heat soaked. Shoebox has a great diagram and tip on how to keep it cool on his website.

 

well I think I can rule out the ICM being heat Soaked due to the fact that the car misses out from the point I get in it and start moveing till about 10 minutes of driveing time then it starts to clear up, unless there is a break in the circutry in the icm and the heat is causeing the connection to close when it expands????

I'm not totaly convinced its the opti either. I've been reading on these forums for about a week befor I registered looking for any ideas. I've seem ONE topic that comes close to what I am describeing and he has not found a solution to it yet. So this is makeing me nervous.

 

man I have been so paranoid about the opti i did'nt even think about the ICM till now, I'm going to go pull it and get it tested if not just replaced, its only a 61 dollar part.

 

Sounds more like a vacuum leak to me honestly than an ignition problem. Make sure your entire intake tract is sealed up well, elbow not cracked around TB, sealed all the way around it etc.