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Hello, im currently working on my 89 iroc z. Car is completely stock as ive owned it for a number of years. It was carbed at one time but ive decided to return it to tpi. Im at the point right now where im needing to time the engine and do some of the vacuum lines. The vac port 'C' on the passenger side (pic attached) when capped will kill the engine. Im aware the this port is for the purge evap system that is currently not operable. My question is why would capping this port cause the engine to die, am I missing something? Timing is set correctly, est procedure was done. Cant be a good thing to have a huge vacuum leak while timing. Any thoughts on this would be greatly appreciated as i have read that you can simply cap this port off.
Random musings from laying in bed, unable to sleep here.
If it dies when the port is plugged then it’s likely not getting enough air from the IAC and your leak is allowing it to run.
also could the TPS be not adjusted correctly? It’s been a while since I had TPI and can’t remember how poorly a mis-adjusted tps can’t make the car run.
years ago I had the opposite. I had forgotten the egr port under the TB on my LT1 swap. With the MAF unplugged it would run and idle insanely high at 3000rpm. But with the MAF plugged in it died immediately.
all boiled down to unmetered air. With the MAF plugged in it was injecting far too little fuel compared the actual air the engine had. So so lean it just died immediately. But with the MAF unplugged it ran in SD mode and injected enough air to match the MAP and load.
Thanks for the reply! Your answer to the issue makes perfect sense. I changed the iac, the old one was toast, internal pieces crumbling from within. I'm going to search for the correct way for the iac to learn it's position. Thanks again and thanks to all the members here for all of their info and knowledge of our third gens.
After setting the iac and tps the car would idle with that port capped off although be it rough. Looks like some more tuning is in its future. You were spot on with your diagnosis.
