"popping" sound in inlet.

[robprice]

I was just hoping that maybe someone else might have had this. It used to happen with my factory engine a little but with the new one it happens everytime i back off the throttle. (even after light tapping) Im pretty sure its just the trottle body snapping shut and sounding through the inlet due to my modified (read halfa) airbox, but it seems to be happening heaps the last few days, and very loud. at idle it can often,( normally when cold idleing) just sit there with the rpm fluctuating between 700 and about 1200 rpm and popping heaps. sounds like its not going to idle and the computer is blipping the throttle to keep it going. It idles fine most of the time. the throttle body was snapping shut ans sometimes getting stuck there but i ajusted the back stop screw and fixed that. If i ajust it any more it idles high. Anyone have a clue? I can live with it but its annoying me now, and getting a few looks at traffic lights!

[Cosmo Dude]

A quick reminder of which Astina/engine you have and what alterations have you made to the induction.

Thanx

[robprice]

ba, 1.8lt (from the land of the rising sun) airbox has had the bottom removed. when i run a pod filter (rarely, due to not being best friends with highway patrol and their defect book) the problem is the same. afm is factory. poping is almost definatly coming from the inlet track (99% sure throttle body).

[Cosmo Dude]

Sounds a little like a deceleration valve not workin'

There are two odd looking devices on the non-throttlebody end of the intake manifold, one is the VICS device and from memory the other controls deceleration (or the final 10-15% of it). Check the plugs and plumbing around there.

Else check the IAC valve; turn the A/C on at idle and check if the revs rise or fall.

[robprice]

thanks heaps, im on it. just out of curiosity are you a mechanic or sumfn???

[Cosmo Dude]

Technicaly minded, I enjoy tinkering too much to do it proffesionaly


I'm a telephone (PABX) tech by trade, enjoy the product but hate the way people use it.

[robprice]

cool. sound like a very knowlageable person thats all. impressed me anyway! Thats why i stopped installing in-car av for a job. its only fun till you get paid!! Now just a request for a head unit install gives me a headache, and the buisness cards live on top of the fridge. I blame VN commodores!

[Toyboy]

Mines been making the same noise for 4 years now mate,it started occuring when i fitted the pod filter,you said you had the bottom removed from your airbox? well try sealing it all up again and the noise should be gone.
From what ive gathered its caused by the revs kicking up especially when when steering,(if you have p/s)and this causes it to pop through the intake.
Its prolly done it all along but when the full standard airbox was fitted you couldnt hear it cause it was fully enclosed!
Ive learned to live with it,done panic your not alone.

[robprice]

thanks mate. Im not really worried about the popping, more annoyed by the fact it wont idle smoothly most of the time its cold. Nice to know im not alone but. Also i checked the wires and hoses running to all devices on intake manifold cosmo and it seems fine. Also when i put the aircon on at idle it used to rev a little higher, now the revs drop ever so slightly when i turn it on, if that helps.

[Cosmo Dude]

Under the big duct that runs to the throttlebody is a smaller 3/4" or so black pipe. It runs to the IAC (idle air control) valve.
The IAC will lift the idle if the engine is cold or you use the power steering, A/C, rear demist etc... and I'm thinking it may partly control the deceleration.
Take the pipe to the IAC off and spray some lubricant (WD40 kinda stuff) to make sure it's moving freely. May not fix the popping but from what you said it could help other bits. You could also try Subaru upper engine cleaner it's about $18 a can, just follow the instructions and don't worry about the smoke when using it.

[robprice]

legend, thanks once again mate.

[robprice]

i was just playing with a spare throttle body i have, and if you open it up and let it snap shut, guess what noise it makes??? Thats what it is toyboy, youd definatly hear it without all the baffles and **** of the factory airbox. just why does it do it so much now? maybe we'll never know, but im playing with the valve thing cosmo suggested as we speak. any luck and ill tell ya mate.

[platypus]

me too, only been doing it since i sealed up the exhaust properly, but the noise comes from the intake side... got me puzzled, so i'm jsut making all these extra noises now

[robprice]

the noise is DEFINATLY the throttle snapping shut. i have one in my hand right now making the noise (small things amuse small minds) however, as old mate off the curiosity show (for those old enough to remember, at least i think it was off that show, well some sicence show anyway!) why is it so???? vacuum snapping it shut????? this is going to be fun.

[platypus]

umm they have a big spring on the cable actuator... don't they?

where are you again? i'm coming round

[robprice]

yep, its quite big. im thinking, but its just hurting. Whats the spring got to do with it?? oh you think thats snapping it shut? maybe, just maybe, its done it on all our cars from new and we're just idiots??? souldnt the vacuum actualy be draggiung in air, thus stopping it from snapping shut. i reckon theres something in that im missing. If you want to play with my throttle body ill drive round and throw it at your house if you want

[platypus]

hmm just thinking about it... meybe zero vacumm condition would do it.. its on downshifts and backing off the power on mine.. esp in the higher rev ranges

throw it at the hosue if ya like, just don't break anything!!!

[robprice]

i just pm'd you. glad you took that right! i noticed today that when i go down hill, in say 4th at about sixty, it pops heaps even with no throttle. also if you lean on the throttle in most gears, say 5% throttle, the back off it does it. Ive got two mates who are machenics and they have nfi! now idles smooth with no popping thanks to cosmo dudes great advice.

[platypus]

rightio, central coast crusie to kariong... and back last one to maccas is a rotton egg... have to pop down the hill together... some one said i had sparks come out the back down tapley rd... then i realised it was because it was tapley, and i bottomed out!!!

[robprice]

mmmm luv those central coast roads. you wanna come through copa!!! i once parked for the night in a pothole!
luv kariong hill but, chewed a clown in a vs (monaro lights dont make your pos commodore handle any better fool!) up there a couple of weeks ago. also cained a vy ss in da rx8 (dad driving like a pussy on the straights, but hooking through the bends. anytime you wanna run that hill im up. oh and maccas at the bottoms good motivation too. also macmasters to killcare is a good run. but deadly at night if you dont know it well.