so i got a hotcam and sometimes the car will idle smooth (at about 900rpm)for a bit then will break up and idle erratic between about 6and 1100 rpms. could this be due to low vacuum causeing the erratic idle or something else?
where should i start looking, valve adjustment (how much past 0 lash should i adjust for a hotcam) all hoses are on and seem to be in good shape. the intake was put on with plenty of sealant. anywhere i should look around the throttle body? what about the idle adjustment screw, should i mess with that any?

throw some suggestions my way, thanks

 

Have you used a vacuum gauge to see how much vacuum you are getting?

 

checked and it was only about 7-8". would the rings not being seated yet have anything to do with the low vacuum? the motor only has about 500 miles on it so far

 

Should see somewhere around 14-15" at idle with that cam. Try readjusting the rockers with the motor running and go 1/4" past zero lash.. lock em down tight.

Ring should seat almost instantly. If you have 500 miles and are still burning oil then thats a big problem.

 

not burning oil, i just didnt know if they would need more time for a better seal. (im a new engine newb) anyway, ill recheck the lash, i think its at 1/2 past 0, but there isnt anything to "lock down tight". rockers are comp magnum 1.6 roller tips.

 

is vacuum the same regardless of idle quality/speed?

 

pull the dipstick with the motor running and see if you feel any breeze coming out of the crankcase.. that will tell you if the rings hadnt seated. Or do a leak down test.

 

scan showed a lean reading on the left o2 sensor. replaced sensor and erratic idle went away and vacuum is now at 13-14"

 

easy fix, sweet. try readjusting the valve lash, you maybe able to get that reading alittle higher.

 

its about time i had an easy fix. i'll prolly tweak the valves sometime to get a bit more vacuum, but so far so good i think. i am wondering if a little cam surge at idle is normal for a hotcam or not, but overall its improved a lot.