i have an Idle issue, where some times, if I thro the car in neutral and coast, my idle revs a few times from 900-1300,and then settles. during this time my WBO2 swipes from 14.7-17+..and just sweeps with the idle. occasionally it will do this as i roll to a stop, and every now and then it dies, but i am able to start the car back up without an issue. The Fuel pressure doesn't seem to sweep, it stays steady @ ~48psi. It pulls ~ -20 to -22in Hg during this sweep, my idle when normal is around -19inHg. I always let the car warm up (~8-10 min) before i take her out, and this is usually after awhile of driving. I am not boosting right now b/c this is a fresh build with ~700 miles.

Ive checked:
IAT connections
TPS connectons
New CLT
CAS
MAP connection
Upstream O2 is tight (ive had a prob where its been loose in the past)
Jut put in new spark plugs,
I have MSD wires, not to old.

I dont have an egr/evap, every thing is blocked off and removed, so no wires burning on pipes issue.

Engine: 5SPD
built bottom end
walbro 255
Hahn PF setup
MP 60mm (clean from rebuild)

Thanks for the help guys.

Remove your IAC valve, thoroughly clean it with brake cleaner, check the tip seal, and reinstall with a new o ring. Also check your throttle spring and cable play. Make sure it's all adjusted properly and up to snuff.

Since you are running an MP 60mm, I would recommend you also set the throttle spring to the tighter setting. It takes a little getting used to, but it helps keep the throttle plate fully closed during coasting.

Could also be a small vacuum leak..

1999 Eclipse GS
Built motor
Hahn 16G Turbo w/ FMIC
Hahn Stage 5 Portfueler (270's & 500's)
Zeitronix Zt-2 wideband w/ 3.5bar MAP
3" SS Turbo Back
CM Stage 4 Clutch and Fidanza Flywheel
Baer Big Brake Kit

Vacuum leak.

You didnt mention if your speedo works.

speedo works fine, minus its off bout 10mph..possibly due to the 355 trans and quaife?

i just changed the plugs, running ngk bkr7 gaped @ .35..i drove it, now afr sweeps, from like 13 to 17...and then when i come to a stop it just dies.. now its every time i come to a stop it just dies. i can start it back up just fine, but now its dying and doing the rpm/afr sweep every time i throw it in neutral. Im cleaning IAC, looks ok, cleaned it any way, the resistance on pin 1 and 4 is 50 ohm and pins 2 and 3 is like 48 ohm..

TPS also checks out with 5.4K ohm across out sides, and it smoothly sweeps resistance with t-plate..

NOTE: it has also got a mean back fire.. when i let off the gas and compression brake, it grumbles then i get a few loud ass pops...

Could be a vacuum line if you havent checked those. Also might wanna check your coil is there any certain outside temperature it does it at or more frequently like when its cold does it seem to do it more often. Could also be a bad ground I had a bad ground in my little project neon i picked up a couple months ago and it was doing all kind of crazy stuff- gauges would go crazy temp gauge would show all the way up would have erratic idle loss in power heck I even had a fire under the dash.

well, seemed TB was leaking, fine fixed it.. now its not my idle thats wierd.. first time ive said that lol.. I idle fine, its when i shift that the issue come into play... when i shift, i see my wb02 go rich , then lean then back to normal..and if i roll on highway , then go N to a stop light, it goes way rich and works itself down to where it needs to be.. idk WTF? changed o2, map, TPS..

could this be a speed sensor issue? my spedo is high by like 10 mph..

As long as your car idles normally in terms of RPMS's, I wouldnt worry too much about how the AFR evens itself out after coming to a stop. Its pretty normal for the AFR's to bounce back and forth between rich and lean as the computer works to try and maintain a stoich AFR.

As long as you are not staying at an overly rich or overly lean AFR for an extended period of time, or while cruising, I wouldnt really worry about it.

Just my 2 cents..

yea, my only issues is its never acted like that before...when i shift its always gone lean then right to 14's...now some times it does that, sometimes it gores rich like 12.5-13 then sweeps lean, and back to the 14s..idk if its a speed sensor, cas or maybe a sticky injector...