91' std w si tranny and mpfi swap.at idle the motor drops from 2k to 500. just replaced o2 sensor and still get o2 code. also iat code. also had to replace cat so something cuasing me to run rich. help me.

 

ttt

 

does it surge back and forth between the two? If so I'd say vacuum leak maybe.. check your hoses... although 2k does seem a bit high. What's happening is your cylinders are being flooded and it's causing the idle to surge..as a result of no vacuum.

 

yes it surges back and forth. i've checked the hoses but i'll look again. it just started doing it one day after opening up on the freeway. then it was only intermittant but now it does it all the time. it progressively got worse.

 

That happened to me after I switched to a 4 wire O2. I resetted the battery and it did it again. I let it idle for about 5 mins and it went away on its own. Weird, never happened again. HTH

 

Thermostat causes this aswell.... Or low coolant(I know this for sure on the newer Hondas)....

 

okay i fixed it.the idle adjust screw had appearantly backed out on it's own. adjusted it and car idles at 1300 w/ no drop. would this cause the #1 code? i guess i'll go reset the ecu and see.

 

not fixed . drove around the block and idle is surging again.