Hey everyone-
looking for some good tech feedback on this subject. I have a ZZ4/T56 combo in my 89 iroc. I went from a auto4 with factory dual cats to a T56 and gutted cats.

The problem-
At idle now, the ecm hunts alot dipping 500 rpm at times. Thier is no performance loss under power, but the idle is annoying. I have a stage 5 chip from tpis (I know, I need to burn my own)

Does gutting the cats have an effect on the ecm?
No trouble codes are setting.

Also, I can watch the gauges during bad idle and see that they twitch at times as if thier could be interruption to the ecm from a sensor and I see it in the gauge movement and feel it in the idle. Hmmmmn

 

im not an expert on third gen ecm's but heres what i do know, there are no electronic sensors behind the catalytic convertor so therefore the computer has no way to tell if its gutted or not. My SS does have 4 O2 sensors and with my off-road pipe i had to install O2 simulators to trick the comp into thinkign i still do have cats, works fine. i know there is an air pipe going to the catalytic convertor on most if not all 3rd gens, now if that pipe affects some type of flow that gets measured, i dont know. but BOTH my 88 irocs ran fine with that pipe removed and sealed off....thats all the help i can be...maybe its an IAC issue or MAF issue

 

THANKS! I do believe what you say because of the no sensor issue.

 

Your problem lies somewhere else. I gutted my cat and the car is fine.
The car could 'twitch' like you said at idle if a spark plug wire fell off. That's what happened to me. I thought the Tach was going bad because it was twitching so weirdly and I didn't notice much of a performance difference. Check all your wires and plugs

 

when did you problem start? when you swaped form auto to manual or when you put your zz4 motor in?

It kind of souds to me like an air leak promblem and tpi is verry sensative to air leaks.

 

I have an 89 with a zz-4. Cat gutted also. Ran fine with both blocks. I agree, it sounds like an air leak. I would scan the O2 sensor, see where it is voltage wise.

 

gutting your cat don't have any thing to do with anything other then emisions