new exhaust => low idle

[cpginkpt]

Got a new catalytic and muffler. The cat is a Walker from Rock auto, but my exhaust shop had to fabricate some pipe and said he ended up using a muffler from a Honda Civic.

The muffler pipe is definitely small and I can see the connection from the cat to the muffler is downsized (pic)

When I picked it up I notice it idles much lower - HOWEVER he also has not hooked back up the downstream O2 sensor yet since he got the wring sized flange and had to order..

So I am wondering - is the low idle from the missing O2 (we will put it in next week) OR is it perhaps from the downsized muffler pipe?

Thanks.

'88 4x4 5 sp

[kamesama980]

At what RPM is it idling?

Did the battery get disconnected? Any other work done up front? vacuum leaks?

So you have TWO O2 sensors in 88? cali emissions I take it? downstream should have no effect on the idle, it's only there to verify the cat is working.

It's unlikely the smaller muffler is causing a lower idle, while it may be more restrictive, idle is when it matters the least.

[cpginkpt]

sub 1K on the idle.

I think you answered it for me. No affect due to smaller pipe and the downstream cat will not affect idle, so I will get the exhaust work completed and look into other options after that.

It was decent idle (1100-1200) before the work done except for when I turn the heater on it would dip to 1K, so exhaust work could just be a coincidence I guess.

[originalkwyjibo]

11-1200 rpm at idle is too high. Idle speed should be 750 for A/T and 700 for M/T.

[cpginkpt]

ah, got it. Pretty sure she would stall at that low an idle currently - guessing I'll brush up on the "low idle" and "leaky vacuum hoses" thread ;)

[kamesama980]

ah, got it. Pretty sure she would stall at that low an idle currently - guessing I'll brush up on the "low idle" and "leaky vacuum hoses" thread ;)

lol That was going to be my suggestion: fix what causes it to run poorly at proper idle.