Hello,
As of late, my c4 corvette has been having weird issues when starting up. I recently had a fiasco with the fuel pump/filter and sorted it out timely, so I hope to god it isn't something to do with the fuel delivery system. Anyways, when I turn the key to start the car, there will be times when it sorta "half" starts, as if the motor doesn't fully come to life. When this happens, the car runs incredibly rough, the RPMs begin to drop below 500, and basically stalls on me. The problem doesn't really go away if I put it in gear, either. However, whenever this happens, I just give it a bit of gas to keep the RPMs up and it eventually fixes itself in about 10-15 seconds and runs as perfectly as ever. The worst part about this is that it happens completely randomly. I've experienced it when the car has been both cold and warm. I shorted the OBD1 connector to show see if it would throw any codes, but nothing comes up! As I said, there will be times when the car starts up completely without an issue. I don't really mind having to give it a bit of gas, but it really does worry me. I'm beginning to think it might be the optispark going, as my car has around 80K miles on it and the previous owner never took care of the optispark issue... However, from other forum threads that I read, a lot of people say it could be the IAC or TPS... Any input or experience with a similar problem would be much appreciated

 

I'm sure more experienced folks will opine. I hesitate to offer my opinion, it may not be incredibly helpful since I don't yet have the end of the story to share--BUT, same issue, '96 LT4. Happens about one startup in 12 or 15. After a lot of reading and a little interaction on the forum I pulled the IAC valve and cleaned it up, but the failure case occurred again a few days later. So I replaced the IAC valve with a new one. In the meantime, though, I'm doing a full fuel delivery overhaul, from fuel pump to injectors, so the car is still apart....thus, no conclusion yet on whether the IAC valve fixed it. Just wanted to reply and say, my relatively novice bet is the IAC based on my prior readings. It costs about $80 to find out...

One difference, though--mine doesn't sort itself out in a few seconds like yours...

 

Thank you for your input, C44EVR. Been reading through various past threads and IAC seems to be a common issue. Figures. Well, I might as well try replacing it, it's probably about time I did anyways! Sorry to hear your corvette ain't running so well, that's a real shame. Good luck with revamping your fuel delivery system, make sure to keep me posted on how it goes!

 

Welcome Alex,

EFI rule number 1
basic tools are mandatory. All vehicles.
Fuel pressure gauge, Adjustable timing light. Yes, old fashioned. Diagnose, even modern coil packs. instantly. Scan tool, better yet, data log. Multi meter.

Easily, efficiently rule out common parts.
You mentioned no codes.

Fuel pressure. currently not critical.
That said.. Valuable info.
(1) wires, cap & rotor condition. Last Replacement/s.?
(2) TPS validated, baseline voltage. ?
(3) IAC counts.? Again, Valuable info. Pull & Inspect cone.
(4) coil. Can Ohm out High VS low side.
Can fail 3 different ways High, low, Both.
(5) air temp sensor. fails different ways. Common, hard re-starts. Or simply hard to start.
(6) ICM. Typically.. Straight up. Fails. No spark.
can you, validate. Spark.?
Fact. The original Opti's reliability, fairly elite.
80k on the clock. I'm sure never looked at.
Especially below 100k. almost rule this out.
Typically a mis-fire code. Can be found.
A timing light is perfect, giving you spark, stobe visual.

Keep us posted. With diagnosis results.

 

If you have a ‘96 it should have an OBD 2 , not an OBD 1. Can check for codes with any cheap code reader.