New to the forum,and would like to thank all for the great info...
In a nutshell,I have an 89' 305/TPI IROC. I recently had the intermediate pipe replaced(3' flowmaster catback-only mod)and the car has developed a start/idle/knock issue. The only codes I get are the o2 and egr sensors. When attempting to start the car(always had the "hot start" problem)-if I hold my foot down it will catch,otherwise nothing. I notice the oil gauge takes a bit of cranking to start to go up,and when it starts it puts out a good bit of smoke(blue) and won't idle on it's own. If I keep my foot down slightly I can keep it going but with a knock. I changed the oil and filter and before I get into replacing many sensors,was wondering if this sounds like simple timing problems(especially since it is knocking). After the exhaust was fixed is the computer rethinking and resetting?

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*1989 IROC Z(White)
>305 TPI/700R4
>Flowmaster 3" Catback
>K&N Filters
>50k miles

 

If its knocking you need to retard the timing, you don't want to damage anything. The computer shouldn't need to change anything at all because of the exhaust being changed.

Change the 02 sensor, that is very important to how your car runs, but I don't believe it will affect how the car idles in open loop(before the car is at operating temperature). Are you getting any codes? Does the service engine soon light ever come on?

The blue smoke is probably valve stem seals, thats a common chevy problem. Not too bad unless you are embarrased by how it looks.

 

Thanks for the reply,just 2 codes o2 and egr.These codes were there before the exhaust was fixed and are still present. I can't keep the car running to set the timing,I'll just have to set it and give it a crank. Can a o2 sensor or malfunctioning egr valve create this many problems...and especially literally overnight. The only clue I had prior to this was my idle the night before was high and would not settle-even driving(stop and go).
Thanks for the info any other ideas on this?

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*1989 IROC Z(White)
>305 TPI/700R4
>Flowmaster 3" Catback
>K&N Filters
>50k miles

 

Anyone have any ideas,desperate here...thanks!

 

No, the o2 sensor and egr have nothing to do with how your car starts. The egr is only used at high speeds, and the o2 sensor is not accessed by the ecm until the computer goes into closed loop.

Try spinning the distributor with the est unplugged and then cranking the engine, do that a few times in different locations to see if you can get it running, if not look for trouble elsewhere.

Have you tried resetting the IAC and TPS? You should look into that, and maybe clean and lube the throttle plates and the IAC passages and pintle.

 

Could be you mass air sensor
When mine went on my Grand Nat
It went somthing like that.

 

I haven't looked into the iac and tps yet,I was simply amazed at how it could go from smooth to nothing in one day. As I said before,the idle was high the day before on my way home and wouln't settle even at traffic lights.I'll try bumping the distributor first.Correct me if I'm wrong the est wire is the single tan/black wire on the passenger side right?

Would a mass air sensor set off a code?Also could the mass air cause this much trouble at once?

Thanks everyone-I'll post results...

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*1989 IROC Z(White)
>305 TPI/700R4
>Flowmaster 3" Catback
>K&N Filters
>50k miles

 

Forgive my ignorance here...for the computer to learn the new values is it necessary to do both iac and tps at once?The iac is easy enough to set,but the tps needs to be set precisely and I don't have access to a meter.Can this be set "by ear".