Idle, low rpm bogging and studdering.

[irjoshy]

Well i've been away at pittsburgh for the past few months and I've been yearning to drive my car, well I just got it back from getting a rebuilt transmission(which is sweet) so i wanted to play around with it, and it seems to have developed a lumpy idle(like a v8 with radical cams), its fluttering and sputtering in low rpms, after it gets to higher rpms it feels like i hit a nitrous button, and the performance comes back.
this has been going on all week
t25
12lbs peaking to 15
homeade UICP w/ 1gbov
turbo back exhaust w/ catco high flow cat
act 2100

what could this be?
could something have been fubared when the tranny was taken out/replaced?

could it be
-the throttle position sensor?
-boost leak?
-clogged cat?
-fuel injectors?
-does the computer need to learn its fuel curves again?
-bad turbo?

I would GREATLY appreciate some help, I go back home on sunday and I really want to drive my car, because I won't get to see her for another month.


thanks guys
-josh

 

[DSMTalonAWD51]

if it drives fine under high boost eliminate boost leak. If its an ecu issue it should go away within a day of driving. Sounds to me like you should check your timing and make sure everything is lined up. Maybbeee fuel injectors, but probably not.

 

[irjoshy]

thanks, I'll keep that in mind.

my mechanic thinks it might be the throttle position sensor?

 

[skelly]

If the transaxle was just removed and reinstalled, then they had to have jostled the engine around a bit. In doing so they may have inadvertently affected your throttle cable linkage - I believe the same problem has stricken my car as by removing the TB elbow last night I discovered that the TB plate was not closing all the way - seems to be the result of the cable linkage being too tight. I might have discovered this by simply disconnecting the cable and moving the place by hand, but one the elbow was off, the two TB gaskets were destroyed, so I had to make new ones. Tonight I should be able to verify one way or another. You might be able to discover this on yours without removing the TB elbow - just try disconnecting the throttle cable from the TB armature, and see if the idle improves. If not, then the TB plate is probably okay with the cable attached as it was.

- SK

 

[irjoshy]

thanks,

I'll check that out tonight. If i ever solve the problem I'll post the solution.

 

[skelly]

Though it was "a" problem, that throttle cable ended up not being "the" problem as I've found tonight. I had so hoped In the case of mine it seems like a vacuum leak because the boost/vac gauge on the dash bobbles around when it is stuttering - does yours do that?

I can't find a vac leak for the life of me. I have a couple exhaust leaks that I'll be taking care of in the next week or two here and if that doesn't correct the problem, then I think my next step will be to remove the intake manifold and clean everything up and get a good look at all the components and make sure there are no split/broken/craked vac lines, etc.

I just got my car used and it looks like somebody may have ran it without the oild cap on at some point because pretty much the whole engine bay is coated in nasty, dirty-caked oil, so it's difficult-to-impossible to get a detailed view of things without removing and cleaning them off first. I think I'll hook up an external vac gauge before I go to all that trouble to verify that the vacuum is indeed unsteady and that the dash gauge isn't lying to me.

- SK

 

[irjoshy]

well, i'm holding boost at 14lbs constant, not even a boost spike. but i have no vac guage to tell you how that is.

I was going to try the throttle thing that you mentioned, but i havent had time.

Something that I just noticed is the fact that if I let the car warm up after about 10 minutes, the engine idles up and the lumpy noise is gone, and when i drive it, it is fine.

However, when i do NOT let it warm up it runs the same way it did when i first posted.

Don't know if this helps or not, I've given up on fixing the problem before i go back to school tomorrow


-josh

 

[beat90tsi]

Could be the FIAV, which is supposed to riase idle during warmup, but I doubt you'd need that to function correctly at this time of the year in Ohio.

 

[ColdAudio]

first of all, do not ever rely on the stock gauge, ever

aditionally, i had crappy idle with jumpy vacuum due to my car running waaaayyyy too lean, solved with afc, not saying that it will be your solution but it may be something to consider