6 bolt swap weird idle

[dsmike1]

this is my first post, so please excuse me if i am posting in the wrong section. im still getting used to this forum setup. Here's my question' my buddy just bought a 98 gst spyder with a 6 bolt already swapped in. It has 272 cams oversized valves, and its ported and polished. It has a big 16g and a stock bottom end, with no fuel upgrades. The problem is it surges at idle once in a while, other times it idles fine. also every time the engine is free reved, it studders and idles very low when the throttle is snapped shut, then it surges a few times and quickly idles good again. I ruled out the iac, and any vacuum leaks. i did not do the swap myself but the wiring harness looks like it was modified perfectly and all the connections are soldered and shrink wrapped. has anyone else had this problem? any help would be greatly apreciated. thank you.

 

[khartley]

Once it evens out, what rpms does it idle at?

 

[dsmike1]

I've been messing around with the idle speed for a while and I have it at about 800 rpm. When it evens out it stays there most of the time. And sometimes a little higher around 1100 rpm.

 

[khartley]

The symptoms it has when revved sound similar to a bov being vented to the atmosphere, so check to see if that could cause problems. From what I have heard, the 272 cams should cause a very light lope in the idle. The cam sensor may need adjusted, that could easily cause a funky idle if it is set too advanced or retarded. I would get a timing light and check base timing.

 

[dsmike1]

The bov is recirculated. The 272 cams do have a slight lope when it is idleing correcctly at 800 rpm, the problem is more of a surging up and down as a vacuum leak or a faulty iac would cause. I have heard about the cas being out of time and cause poor idle so I adjusted it forward then backward and saw no change so i put it back in the midle where it was. I will bring a timing light home from work tomorrow, do you know what the base timing should be set at? or would be good for the cams if it makes any difference. ill check the chiltons manual for stock base. Thanks

 

[khartley]

Stock base is 5 degrees. Another thing I've heard of is the BISS o ring leaking, an easy way to tell would be to put soapy water (or spit) in the hole and look for bubbles. While your at it look for other leaks, could be a boost leak but I doubt it.

 

[iminadaze]

It has 272 cams oversized valves, and its ported and polished. It has a big 16g and a stock bottom end, with no fuel upgrades.

Well theres your Problem...get a bigger FP, bigger injectors, AFPR, and then have it tuned...

 

[khartley]

That has nothing to do with his idle.

 

[dsmike1]

yeah i doubt it is a boost leak because it is an idle problem. and the fuel is fine for now at stock boost settings and a giant front mount. stays rich all the way up to 11 psi.

 

[TurboFritz]

yeah i doubt it is a boost leak because it is an idle problem. and the fuel is fine for now at stock boost settings and a giant front mount. stays rich all the way up to 11 psi.

i wouldnt rule out a boost leak, if its stock maf it is a good possibility, i know mine was stubborn when i first bought it though if it drives good but just wont idle then i guess that could be ruled out. could be trottle position sensor, if its gettin worn it might not be reading fast enough to catch and idle.

 

[dsmike1]

Good idea on the tps, I'm gonna bring my bosses modis home thursday after work and check out everything. Thats when I will check/ adjust the ignition timing too. I'll post results after.

 

[dsmike1]

So after some time using the snap on modis, I found that the long term fuel trin is +12 and the short term is +4. The 02 is reading .06 volts, so it is a litlle rich at idle. and obviosly its constantly trying to richen itself up. The strangest thing I came across tonight is that the ignition timing. While whatching the timing advance on the scan tool, I adjusted the cas back and forth, with no result. It just stays between 11 and 14 degrees btdc. Im stumped, What would be keeping it advanced so much?

 

[BLINKY619]

So after some time using the snap on modis, I found that the long term fuel trin is +12 and the short term is +4. The 02 is reading .06 volts, so it is a litlle rich at idle. and obviosly its constantly trying to richen itself up. The strangest thing I came across tonight is that the ignition timing. While whatching the timing advance on the scan tool, I adjusted the cas back and forth, with no result. It just stays between 11 and 14 degrees btdc. Im stumped, What would be keeping it advanced so much?

could it be that its not hooked up...??

 

[dsmike1]

I think it is all hooked up correctly because a few times when I turned the cas counter clockwise, which im pretty sure is advancing, it would just stall out. Which makes sence. To much timing and an engine won't start or run

 

[dsmike1]

ive been away from this site for a while and noticed this old thread so i figured i would update. turns out my buddy wanted to buy my evo 8 injectors and wally 255 so i sold them to him and we installed them. car idled mint. i have no idea what the actual solution was but it was resolved.

 

[Cornfed4G64]

was all your fiav hooked up?