Rough idle when cold

[saint]

My brother owns a 1993 GMC 2500 with a 350. It has about 200,000 kilometres (120,000 miles) on the truck and for some reason it seems to idle roughly, but only when the engine is cold, and not every time either. Once the engine warms up it seems to be fine. Any ideas?? I thought maybe the rotor or wires, but then you would think it would be rough idling all the time, not necessarily when the engine is cold.

[bbb]

intake gaskets a common problem

[BlackTaz]

If it's similar to other GM V-8's, it sounds like an idle air control valve to me. You can take it apart and clean it, which might help. Or, you can replace it. I had a very similar problem with an intermittent idle problem... it wouldn't start without part throttle and would idle like crap, but only 20% of the time.

[JayMan]

If it's similar to other GM V-8's, it sounds like an idle air control valve to me. You can take it apart and clean it, which might help. Or, you can replace it. I had a very similar problem with an intermittent idle problem... it wouldn't start without part throttle and would idle like crap, but only 20% of the time.

 

Thoroughly clean the Throttle Body and the Idle Air Control passages. If you also have hard cold starting, stalling, etc, deposits on the air control passages in the Throttle Body are usually the culprit.

 

Make sure to use the proper Throttle Body cleaner, one that states "certified safe for coated throttle blades." Regular carb cleaner is too strong and can dissolve the TB blade coating, which will flake off and be injested by the motor.

 

Do this first, it's a lot easier and cheaper than checking intake manifold gaskets.