I just bought a 96 T/A from my buddy today, and I'm trying to get it running good. It has a 94 corvette motor, with the LT4 hotcam kit.
It idles really weird, different than how a normal cammed motor should.. sometimes it tries idling at 500 rpms, other times its around 1100 rpms.
Also, it seems at low rpms, under load it really dogs down, like a major miss or something.. then all of a sudden, it kicks you back in the seat, almost like a nitrous hit, when it starts running right.
If you give it a good amount of throttle, and go through the gears, it seems to miss every once in a while in the higher rpms, between 3500-6000.
Another thing it does, is when you're slowing down to a stop sign, it'll often stay revved to about 1500, until you make a complete stop, then bounce down, and go around 800ish rpms, and idle like crap, nearly dying. Sometimes it almost feels like it's giving throttle for you as well, I could idle through town in 3rd, because it was around 1500 rpms for whatever reason.

Now, do I simply need a tune? I just put in a Walbro 255 pump, and it did it before and after. My friend recommends getting a fuel pressure regulator.. Would that do anything?
What about optispark, could it be that? It's a fairly new one, we put it on when we swapped the motor in, about 500 miles ago. (motor has 30,000 miles)

 

Missing and stumble sounds like an ignition problem to me, irregular idle may be something else. Is it throwing any codes? I would check plugs and wires and test the icm and the coil.

 

It has had a SES light for a long time now, it's missing the rear 02 sensor, but I would imagine it's throwing some codes. I suppose it wouldn't be a bad idea to get it tested..

I'm starting to think its wires arcing or something, it drove fine on the way home.. After I cleaned the car up a bit, it just starting running like crap, so it doesn't sound much like a fuel problem now that I think about it.

 

Oh, and that reminds me, it really does shake a bunch at idle, I'm assuming it's stumbling from a cylinder or two missing. I should know in an hour or so

 

Get the car scanned for codes. The rear 02 sensors do not impact driveability, they simply monitor the catalyst efficiency. Getting an aftermarket tune would simply be trying to bandaid a problem.

 

Well, no arcing going on.. At least as far as I could tell.

Any other ideas?
How do I test the icm and coil?

 

You can take the coil and ICM to AZ and they can test it. Inspect all of your wires thoroughly.

 

Shbox has a good writeup of testing the coil and ICM, go check out his website. And also while your in there do the opti test too.

 

You indicate it has a 94 engine. But the car itself is a 96 T/A. What PCM are you using... 94/95 OBD-I or 96/97 OBD-II? If you are using an OBD-II PCM, what was the "fix" for the 94 engine not having the crank position sensor, EVAP vacuum switch, incorrect knock sensor impedance, etc.? I'm assuming you have the OBD-II PCM , since you wouldn't need the after-cat O2 sensor with OBD-I.

Since you are thinking about replacing the fuel pressure regulator, and have replaced the pump, have you ever tested the fuel pressure?

Was the PCM tuned for the LT4 HOT cam?

 

I'm honestly not sure what has been done for that stuff, but I'll ask my friend (person I bought it from) soon, and post it up.
And I'd assume I have the OBD-II PCM still.
Would any of those things cause this misfire/dying when it gets warm?

I just did test the fuel pressure, definitely good and strong.

Hasn't been tuned yet, still stock.

 

If I am not mistaken, if you have a bad opti, or burnt wires, arcing, ect...it should stumble/missfire all the time. But if it only stumbles and missfires when the car heats up, it could be an indication of a bad ICM, or an open/closed loop issue.

 

New Update:
Just went up to the car to take it outside and wash it off (it was FILTHY) and it would not idle whatsoever. It would barely run even if I was giving it gas..

I'm stumped.
Oh, and I ordered an Opti.

 

I might be off but that sounds like the opti spark system. My friend washed his engine and it wouldn't wanna run after that. Apparently you are supposed to cover it with a bag. His car was running a bit like yours and when he cleaned his engine, water got in there and finished it off.

 

Yeah, it's really sounding like thats the problem. Hopefully my new opti will fix the problem.

 

Did you check the fuel pressure regulator and the fuel pressure itself as Fred suggested?