I have an 88 Firebird Formula with a mild cam (don't know specs), Hypertech chip, 350 TBI off a caprice cop car, TBI spacer,headers and Flowmaster cat back. problem it it was idling very fast and there was no fast idle adjustment on the Throttle body . It was also running very rich so I retarded the timing and it started running very rough and no matter how I adjusted the timing nothing worked. So I checked the plugs and they were black.

i am figuringthe 350 TBI is too big. So I am going to put a stock 305 Throttle body back on it and new plugs and see how it runs.

my question is could the Chip be making it run too rich and most importantly will any TBI unit from any 305 work?

the engine code for my car is "E" if that has any significance.

 

Could just be sensors or a bad tune on chip o2 iac tpi all would cause that

 

throttle position sensor, coolant temp sensor, bad oxygen sensor. vacuum leak. bad injectors. and more...

 

350 and 305 TB are the same size, the flowrate of the injectors and the tune are different.

 

I would rule out vac leaks first. check all hose for cracks etc. also was the correct TBI base gasket used?

IAC should be closing thern opening when key on engine off. On a warm coolant it should be nearly closed like 95% so with engine running. Do a visual on thatlooking into TB bore at IAC inlet.

 

Ok I will check these things out. Thanks.

 

The injectors being too large for the tune is more than likely your "rich" problem.

 

Good point RF. I assumed the hypertech chip was for a 350 TBI cop car. Maybe a 305 chip.

 

I have a set of 305 Injectors. I am going to try that and change the plugs and see what happens. Thanks

 

problem fixed. Changed spark plugs, put 305 injectors in and re set timing. thanks guys.