I have an L98 swapped into a '90 RS that originally came with a 305. I bought it that way and it has always had problems "searching" for RPMs at idle and sometimes jerking while in gear. The local Chevy dealer said that they couldn't run any diagnostics on it because it was swapped in and the wiring was all messed up.

Could this be true or did they just not want to go through the trouble of figuring out what is wrong with my car?

 

What was the original motor in the RS? You can check by looking at the VIN. Was it a L03 or a LB9?

 

When you say "searching" for RPM's, you mean the RPM's at idle change, right?

If so, it sounds like you have a vacuum leak to me. Have you checked for one yet?

Have you cleaned your IAC pintle and throttle body plates?

 

It had to be TBI since it was an RS, unless it was a B4C

 

Yes, it was originally an L03.

I'll try checking for leaks and the IAC.

Will I be able to check the error codes on my ECM if the engine was swapped?

 

Yes all you need to check error codes is a paper clip. Sorry about the question, but I just had to make sure it originally came with the L03. Since this is the case, its very possible that the wiring is messed up since it needed to be changed (either the TBI wiring was modified, or TPI wiring was swapped in).

 

Crap... my SES light doesn't work. Anyway to check the codes without it?

 

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Seems to be a pretty common occurance with the 305 to 350 swap if you haven't done any tuning.

 

I have a 350 TPI motor running on a test stand. It runs fine unless I use a 305 memcal. The 305 program causes surging. Make sure you have the correct memcal in that ECM for the 350.