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Longtime lurker, first time poster. I have a 1993 LT1 - ran great last summer but this spring it started to stall as soon as I took it out of storage (indoor, heated). When it stalls there is no warning leading up to a stall - so no misfiring, not boggy, no change in sound - the car just shuts off as if someone pulled the key out. This usually occurs when slowing down, coming to a stop, or just coasting without giving it gas. Then I have to wait 5 - 15 minutes for it to start back up. It usually stalls after 10 - 20 minutes of driving. At idle RPMs are about 550.
Yesterday I took it in for a diagnosis - they couldn’t find any vacuum leaks or obvious issues. The mechanic drove it until it stalled and thought it was likely the ignition coil, so that got replaced. When I test drove it that night it didn’t stall, but 5 minutes into the drive I stopped for gas and it wouldn’t start up after. Took 20 minutes to start. My next best guess is the ignition control module, which is likely still original because the ignition coil was. Below is a list of things I’ve tried/replaced this spring.
New radiator (discovered it was cracked and leaking)
New brake booster (was cracked, thought maybe there was a vacuum leak)
New brake booster check valve (also failed)
New battery
New EGR valve (original couldn’t hold vacuum)
Any cracked vacuum lines replaced
Cleaned throttle body
Cleaned IAC
New ignition coil (changed yesterday)
I do also have to change the valve cover gaskets because I’m slowly leaking oil. The spark plugs were pulled and look fine though. Any ideas are much appreciated.
On some rare occasions the Opti-Spark (Distributor in the front of motor) become heat soaked and shut down, now before spending a fortune on the part. If you have a FSM run the Opti-Spark flow chart or find someone who can send you the pages or see if there's a YouTube on it.
Also check the wires at the ICM and Coil, my 93 drove me crazy with the same shutdown turns out it was corroded/broken wires at the coil.
To test for bad wires is simple while car is running just giggle the wires if there bad it shuts down
On some rare occasions the Opti-Spark (Distributor in the front of motor) become heat soaked and shut down, now before spending a fortune on the part. If you have a FSM run the Opti-Spark flow chart or find someone who can send you the pages or see if there's a YouTube on it.
Also check the wires at the ICM and Coil, my 93 drove me crazy with the same shutdown turns out it was corroded/broken wires at the coil.
To test for bad wires is simple while car is running just giggle the wires if there bad it shuts down
Okay, thank you - I’ll look into this. If it an Opti-spark goes bad, does it usually give some sort of warning when the car is about to stall or will it just cleanly die?
They can just shut they can also sputter, also take a look at the coolant temperature sensor in the front of the water pump I had a faulty one and would just shut off but it throws a System failure code
I have a 93 and did have to change Opti because sensor was rusted and corroded. Now remember i bought this new, garaged only, once rained on going to Carlisle after i pulled it off the trailer when it came from Bolling green. The reason for Opti removal and replacement bogging and hesitation. Who would think the Opti was bad, even though i have the original one rebuilt by a forum member. I now have three in stock just in case the OB1 shows a code which it will not for OB1 is only good for nothing. So take your old Opti and have someone rebuild it .A Petris Opti which is a good replacement is $800.00. Make sure it is vented this time
I have a 93 and did have to change Opti because sensor was rusted and corroded. Now remember i bought this new, garaged only, once rained on going to Carlisle after i pulled it off the trailer when it came from Bolling green. The reason for Opti removal and replacement bogging and hesitation. Who would think the Opti was bad, even though i have the original one rebuilt by a forum member. I now have three in stock just in case the OB1 shows a code which it will not for OB1 is only good for nothing. So take your old Opti and have someone rebuild it .A Petris Opti which is a good replacement is $800.00. Make sure it is vented this time
Okay, good to know. Is there a solid way to test the opti? I took it to a shop and they’re pretty sure it’s the ignition control module, but it’s also lots of guess work.
Okay, good to know. Is there a solid way to test the opti? I took it to a shop and they’re pretty sure it’s the ignition control module, but it’s also lots of guess work.
A ICM is cheap in comparison to most things and it can be done by you in 15 minutes for $150 or less.
I was shocked to find they cost that much
Last edited by s carter; Jun 13, 2025 at 10:14 PM.
Also check your fuel injector ohm resistance, both cold and fully warmed up. Injectors that are out, or nearly out of tolerance will short-out when hot and simply stop firing. Likely not all of them, but probly enough to give you these symptoms and kill the engine until it cools. Also the fuel pump or bad relay can do this. Clean the contacts and check & freshen all your grounds. Def no fun getting stranded! Good Luck 👍
Help with solving a new stalling issue?
