I have a 87 5.7 TPI Iroc that is giving me some odd issues. So, I have a slightly rough Idle with the check engine light on (no codes stored) but, the car still has most of it's power. Then, the check engine light will go off and, have a completely smooth idle but, is totally gutless. When that happens I also get a very strong Catalytic converter smell. This happens intermittently for as long as a couple minutes and, as short as a few seconds.

Any ideas what may causing this? Been scratching my head all week and, have came up short on a fix.

 

Based on that description,......... my first GUESS is a bad ECM.

 

the ecm is good. the ignition at the on position has the check engine light then shuts off when the car is fired. I think I found it. It would seem that a purge valve wouldn't let the fuel vapor into the charcoal canister. So, it was over pressuring the gas tank. Then once the pressure got to be so great, it would release and, flood the canister which flooded the throttle body, then down to the cat. I loosened the gas cap and, it all went away. so, it's down to a cleaning or replacing of that purge valve. Hopefully that does it. cheap fix right there.