Car shuts off when warmed up and idling. Starts right up but have to drive with one foot on the gas and the other on the brake? Car has a 350 LT engine with about 5000 miles and came with the car. Any suggestions? I am mechanically challenged. Lol.

[A83]

1983 Avanti with 350 LT engine with 5,000 miles.   Idle drops and shuts off when car is warmed up.  Any suggestions?  My mechanic can't figure it out.  I had to drive with one foot on brake and the other on  the gas to keep the idle up.  The car does have a computer - kind of old and clunky looking.  I am admittedly mechanically challenged. Other than this car runs fine. 

Appreciate any help. 

 

Thanks A83 

[pantera928]

It sounds like you  may need to adjust the idle screw on the drivers side of the carb under the air cleaner or is it fuel injected?

[Kodjo]

4 hours ago, pantera928 said:

It sounds like you  may need to adjust the idle screw on the drivers side of the carb under the air cleaner or is it fuel injected?

With a computer? Does not the computer control idle? If the computer does control the idle, I would say a temp sensor fault. If the computer has no function for the idle, it is indeed the carb. When your "mechanic can't figure it out", I would suggest finding an other mechanic.

[Avanti83]

On my 83 the carb was an electronic unit that the ECM controlled. There should be a OBD port under the dash to access the codes that the computer finds. You may also be able to read them by shorting a couple contacts. You can find that procedure with Google but a reader is cheap on line or at auto stores for those early systems.

The computer system is essentially an add on to the regular harness. I ripped that portion out and used a carb and distributor initially but before you go that far read the codes, even these early ecm's can tell you if there a bad input/sensor in the system.

[Kodjo]

The computer only controls the advance right? No injection or idle speed control?

[A83]

Thank you.  The engine is fuel injected and I was told the computer controls the idle but not confirmed.   Will have the temp sensor checked. 
 

Could a short be the problem as I had an occurrence where the car just shut off after hear a snapping noise with the radio shutting off? 

[Kodjo]

If your car is fuel injected, the idle is controlled by the computer. Unplug the computer and check all wires for breaks. Mostly it is something really simple. 

[Avanti83]

Post a picture of your engine with the air cleaner off. I believe GM only supplied EFI in the cross fire tbi engines in this era. If you have a single tbi or tpi setup it's probably not the original engine.

My point remains, if you have a computer you have a diagnostics port under the dash. Use it to diagnose your system.

[pantera928]

Is this engine original? I thought it would have a 305. I wonder what else is changed

[wildfelr]

RQB3263/81/305.... Does it have fuel injection or carb.?   If carb is it an electronic q-jet ? If elect q-jet it can(should) be replaced with NON elect q-jet(direct 4 bolt replacement w/ one wire hook up)  Im not sure this will  solve your problem but will certainly make your life with Avanti simpler and more enjoyable.... If it has fuel injection may be an intermittent elect  fuel pump..... good luck and let us all know how you resolve this issue ...... BILL 

[wildfelr]

Ok now ive read back..... the TBI system is very simple but still need fuel and fuel pressure (9 to13 psi) from the pump .....BILL

[studegary]

13 hours ago, pantera928 said:

Is this engine original? I thought it would have a 305. I wonder what else is changed

I agree.  A 1983 came with a 305.  If it now has a 350, you will have to search out what components it has.  

[Avanti83]

1 hour ago, studegary said:

I agree.  A 1983 came with a 305.  If it now has a 350, you will have to search out what components it has.  

On the passenger side of the block toward the front of the engine where the bottom of the head meets the block there will be a pad with numbers/letters stamped into it unless the block has been surfaced. Those will help decode the source of the engine. Those plus a picture of the carb/injection setup will help.

Edited December 4, 2021 by Avanti83

[pantera928]

On 12/4/2021 at 11:45 AM, Avanti83 said:

On the passenger side of the block toward the front of the engine where the bottom of the head meets the block there will be a pad with numbers/letters stamped into it unless the block has been surfaced. Those will help decode the source of the engine. Those plus a picture of the carb/injection setup will help.

Good points. Looking forward to pictures and answers.

[pantera928]

On 12/3/2021 at 4:25 PM, Kodjo said:

With a computer? Does not the computer control idle? If the computer does control the idle, I would say a temp sensor fault. If the computer has no function for the idle, it is indeed the carb. When your "mechanic can't figure it out", I would suggest finding an other mechanic.

Well, since we don't know any details other than that the motor is not original, who knows what else is on it. It might be all carbed or something else.

[Rhys]

This was a common problem on Chevy PickUps. It is possibly the module in the distributor. Cheap easy fix to try.

 

[wildfelr]

RQB3263 81/305..... If you go the module route ..... yes and easy to check ....check for spark at two or more plugs....if no replace the module......a 5 minute job.....however.....only install genuine OEM /GM module ....i have had experience with several aftermarket modules  (one lasted 1 mile) and after installing an  OEM unit purchased from GM dealer  been perfect ever since..... (I carry a spare and a screwdriver)......Best of luck.....Bill

[A83]

Thank you all -appreciate all the tips and will pass them on - the Engine is an ATK engine -company is in Texas - less than 8,000 miles on it. The application is a 350 Chev 96-97 LT-1 engine. It is fuel injected. Engine was new in the car when I bought it in May of 2014.

[A83]

Thank you all -can’t send pictures as car still in shop and I am out of town - will get some if I can - going to try to get it to a different shop 

 

thanks again 

 

Kevin 

[A83]

Ok finally - air idle control and throttle body was changed - car runs fine but still stalls when warmed up but starts right up afterward .  this is what they are telling me.  The next thing they are going to look at is the "map" which I think stands for manual air pressure sensor ( could have that wrong) if that doesn't work they are out of ideas. 

 

Any suggestions? 

 

Thanks Kevin 

[pantera928]

Vacuum leaks? Don't recall if that engine has a cold start temperature sensor.

You might try on of the Corvette forums or Camaro forums since the LT-1 was used in those cars versus here where that car originally had a 305

[Gunslinger]

The LT1 engine of that era was infamous for Optispark distributor issues…loss of power and hesitation among them.

[A83]

Thank you all for everything.  Finally got it fixed. After 7 months the opti  spark was replaced and it seems to be running fine.  Along the way the throttle body was replaced and a sensor on the radiator.  Lets hope it lasts.

[A83]

Update - so far so good