00EckoSI

i have a 2000 si and i recently put a hytech big tube header a test pipe and a tsuedo n1 exhaust on my car...now the car idles funny..it only does this when the motor gets to running temp...i have a p0420 code stating that the catalyst is below threshold...i had that before i replace the exhaust but it was idling funny like it is...do i need to put a high flow cat on the car to create back pressure for it to stop doing this? or should i replace the downstream o2 sen. sinice i alreadt replaced the upstream one...i cleaned the iacv..even bought a new iacv and installed it same thing so i returned it...any suggestions?...the car idles from 1000 up to 2000 then back to 1000 constantly while siting at an idle then every once in a while it will go from like 1500 to 1800 very rapidly

delsolproblems

The engine code is a separate issue from your idle problem. The P0420 code is to let you know when your cat is toast. Check the MAP sensor output voltage at idle.

00EckoSI

what am i looking for voltage wise?

delsolproblems

.4-.5v

00EckoSI

and if its not that its a bad map sensor?

delsolproblems

More likely a vacuum leak, one common cause of bouncing idle.

delsolproblems

The MAP sensor is a little vacuum gauge. If it's working correctly, it will show you how much vacuum is inside the IM. If the voltage is off then you start checking vacuum lines and closing off vacuum ports on the IM until you either find the leak or check them all. If no vacuum is leaking and the MAP sensor is off, replace the sensor.

00EckoSI

bump

uhhhh4doors

do you have a o2 spacer on the test pipe to get a different reading the second sensor

00EckoSI

no

MonkeyMagic

so from this i gather that you don't have a cat on the car at all?

newtron63h

just want to clear something up. there is nothing on your car or any car that needs backpressure. what they need is an exhaust system that is tuned to your engine so that you are getting good velocity down low(smaller diameter creates more velocity), AND is big enough to flow enough air so you arent choking it up high. for instance, a 3" system on a d16 or even a stock B16 or B18 is way overkill. it improves top end but kills low end torque, BUT a 3" system is still overkill on the top end too. so something like a 2.5" system should still give you just as much top end gains while keeping the velocity up down low to keep your torque up. NOW all of this applies to daily drivers. most forms of racing dont care one bit about low rpms.

00EckoSI

i replaced the cat with a test pipe and an o2 sensor in the test pipe like i stated on the original post...but to newtron i didn tknow that...the honda guy at the shop said it needs back pressure...im just slow ruling things out to why my car idles like that at warm temps...im starting think its a vacume leak

00EckoSI

but it only started doing this after i put the exhaust on thats why ia sked about the back pressure

THC07

most people relate back pressure to exhaust gas scavenging. which we like

newtron63h

yet scavenging and backpressure are exact opposites.

THC07

scavenging being the evacuation of the air, we on the same page?

newtron63h

yes scavenging is mostly found in headers where the exhaust charge of one cylinder passes the collector at the same time the next exhaust charge leaves the cylinder, this pulls the exhaust out of the cylinder and then the cycle keeps repeating.

ReVeNgEd-SoN

You have no o2 sensor therefore your car cannot adjust it's fuel/air ratio correctly leaving you at a bad/rough idle. It's exactly how my car is, it idles fine when warmed up but wants to cut out when fresh started.

00EckoSI

do people not read what is posted? i see this all the time in posts it drives me nuts....like i stated above i have 2 o2 sensors one on the header wich is brand new and one on the test pipe after the header which replaced the cat

ReVeNgEd-SoN

Just because the sensor is new doesn't mean it works properly lol..

00EckoSI

i didnt say that it would, and the chances of buying a new on and it not working are slim..i know it happens but its slim... u made the comment about not having any..if u would open ur eyes when u read then there wouldnt have been any confusion on your part...

96_cvc_b16

if he bought the sensor brand new, then chances are that the sensor is good. i suggest, as previously stated, you check the map sensor/ vaccum lines. sounds like a vaccum leak to me

newtron63h

put a vacuum gauge on it......should be 17-22 "Hg. and should be pretty stable.