I have a lb9 305 TPI engine (91 z28), the interesting thing is the engine runs amazingly until it is shut off. As soon as it is shut off and restarted, the engine stutters and sputters unless it is WOT. It does not have any codes showing.

I have replaced the MAP sensor and the ignition control module in the distributor. Any one ever heard of this before? Any help would greatly appreciated!

 

I forgot to mention, when the engine cools completely off it runs great again.

 

My experience with small blocks doing this can be a few different issues (usually carbed) but start with carbon deposits, use some carb cleaner clean out the valves and pistons. Also clean your throttle body and Iac passage, start with that see how it runs for you!

 

Could be any number of things, I'd start with above and also check for a leaking fuel injector.

 

Sounds like engine run-on (or "dieseling"). Probably ignition related... once power to ignition is shut off, the engine should shut off immediately.

Try this...

Let the car idle, and then disconnect the power to the distributor coil manually. Can probably just unplug the 12V to the coil. If the engine shuts off properly, my guess is you have some issue that's keeping the ignition energized after the key is turned off.

 

The engine shuts off right away, it doesn't run on, sorry I should have put that better, I juse reread how I wrote that. The interesting thing is I can run it for an hour and shut it off, walk in to Mcdonalds to get a burger and the car will run terrible when I start it back up.

I'll try the suggestions and see what happens, thanks!

 

I edited the first post to reflect what is happening. That's what I get for posting at 2am with sleep apnea lol.

 

Check the ecm coolant sensor.

 

Also check the intake air temp sensor!

 

When you start it back up, it goes into open loop for about a minute. Can you keep it running for a few minutes to see if it smoothes out after it gets back into closed loop?

 

You can keep it running, I drove it for 6 miles running like a pile of crap just to get home. It does not smooth out.