350 trouble

[jb1390]

I have a 1993 chevy 2500 with a 350 engine and automatic tranny, if that makes any difference. When it warms up, it will idle rough, starting by a small dip in rpms, then a rise, back and forth fluctuating more until eventually it will stall. At mid range throttle it will act like it wants to quit, and will act like it runs out of fuel until it hits 700 rpms or so, then it will kick right back in, only to do the same thing again. it is fine when it is floored, no noticable problem. I have changed the fuel pump, egr valve, tps, injectors, and computer trying to solve the problem. Fuel filter, plugs and wires, distributor cap, air filter, o2 sensor are all new as well. This is very puzzling, any help would be appreciated.

[Jacqson]

I have a 1993 chevy 2500 with a 350 engine and automatic tranny, if that makes any difference.  When it warms up, it will idle rough, starting by a small dip in rpms, then a rise, back and forth fluctuating more until eventually it will stall.  At mid range throttle it will act like it wants to quit, and will act like it runs out of fuel until it hits 700 rpms or so, then it will kick right back in, only to do the same thing again.  it is fine when it is floored, no noticable problem.  I have changed the fuel pump, egr valve, tps, injectors, and computer trying to solve the problem.  Fuel filter, plugs and wires, distributor cap, air filter, o2 sensor are all new as well.  This is very puzzling, any help would be appreciated.

 

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It might be vapor lock.

[redvett]

I have a 1993 chevy 2500 with a 350 engine and automatic tranny, if that makes any difference.  When it warms up, it will idle rough, starting by a small dip in rpms, then a rise, back and forth fluctuating more until eventually it will stall.  At mid range throttle it will act like it wants to quit, and will act like it runs out of fuel until it hits 700 rpms or so, then it will kick right back in, only to do the same thing again.  it is fine when it is floored, no noticable problem.  I have changed the fuel pump, egr valve, tps, injectors, and computer trying to solve the problem.  Fuel filter, plugs and wires, distributor cap, air filter, o2 sensor are all new as well.  This is very puzzling, any help would be appreciated.

 

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It might be vapor lock.

Vapor lock is highly unlikely since the fuel is pumped constantly through the fuel system. Have you checked for codes? Has MAP sensor been replaced? It gets bad with time having fuel vapors in it.

[Butch 02 Denali]

A very common problem on these TBI engines is the gasket splitting under the throttle body. It can cause many of the problems you are describing.

 

Second choice would be the water temp sensor in the block, again, a fairly common problem.

 

And both are a cheap fix too!!!

[snoman]

I have a 1993 chevy 2500 with a 350 engine and automatic tranny, if that makes any difference.  When it warms up, it will idle rough, starting by a small dip in rpms, then a rise, back and forth fluctuating more until eventually it will stall.  At mid range throttle it will act like it wants to quit, and will act like it runs out of fuel until it hits 700 rpms or so, then it will kick right back in, only to do the same thing again.  it is fine when it is floored, no noticable problem.  I have changed the fuel pump, egr valve, tps, injectors, and computer trying to solve the problem.  Fuel filter, plugs and wires, distributor cap, air filter, o2 sensor are all new as well.  This is very puzzling, any help would be appreciated.

 

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It might be vapor lock.

 

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Could be but I would also check the gasket between the TBI unit and intake as I have seen a lot of them go bad with age and cause strange idle problems (I had it happen to me on my 89 about 5 years ago)

[evan]

would a gasket going bad cause my 94 sub to have a low idle with air on in drive I replaces the iac and I still only have a 375 idle

[snoman]

would a gasket going bad cause my 94 sub to have a low idle with air on in drive  I replaces the iac and I still only have a 375 idle

 

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Genrally not but geven age of vehicle I would replace it because they do go bad.