I have an 87 iroc 305 tpi . when engine is cold rough idle at start up. but as engine warms up runs smooth any suggestions thanks wes

 

Does it stall, or is it just rough?

Check your plugs, wires, cap and rotor.

 

Marooned Z in MD,

Welcome Aboard!

Felo has good advice. A little more information might help narrow down the possibilities. Is the car basically stock, or have there been modofications? Does it start normally or require a lot of cranking? What is the idle RPM when cold?

 

Its only rough idle when the engine is cold. It stalls like it is going to shut off then suddenly it recovers and runs at a smooth idle at about 1100 rpm then as the engine gets warmer the idle reduces to nomal 700 rpm and runs smooth with no stalling or rough idle. Only when the engine is cold.

 

mine does the same thing.

when you first start it -- fires up good but immediately starts loosing speed and gets rough
but then like 2-4 seconds after startup it will shoot up to like 1000 and idle fine from then on.

sound familiar???

I think it may be something with the cold start injector but I am uncertain...

 

That is my first check point that will test is the cold start valve, I cant see anything else possible. But i will also check the fuel pressure just as well.

 

buddys gta had that problem turned out be be a gasket leak on the intake runner. if that helps

 

Thats another good point to check. Ill also do an leak test to see if that might be the problem. thanks wes

 

Maroon,

IIRC, the cold start only operates wile cranking for a few seconds (the reason it's called a cold START valve), so it the poor idle occurs longer than that, the cold start won't be all of your problems.

By your description, the problem improves once the engine warms, so I suspect you have a mixture issue. Just to verify that the ECM is getting correct information, check the TPS voltage setting, and check the CTS and MAT sensor resistances. If the CTS/MAT are providing false information, the open-loop fuel trim can be way off. Once the engine warms and achieves closed-loop, fuel control is based mostly on the O² sensor, so the mixture would be more appropriate.