weird high idle sometimes

[starr]

ok my 98gst has the 3" LS1 maf, the maft with the rpm wire tapped, and set up for blow thru. most times my car starts and idles fine at around 700-1000rpm. then, every once in a while i'll start it, and it will not want to run, it just chugs, chugs, and looking under the hood the engine is pulsating crazily and looks like the whole thing is going to hop right out of the engine bay. usually i will give it a lot of gas and it will straighten itself out, or i'll kill the car and restart it and that will fix it. thats one problem. the second problem is that sometimes i'll start the car, it starts fine, idles fine, i'll go down the road and come to a stop and i'm idleing at like 2k. then the next stop i'll be idleing at 25k. then the next stop i'm idleing at 3k. i can shut the car off, leave it off for an hour, unhook the neg. cable to reset the ecu, none of that seems to work the only thing that seems to work is just let the car set overnight, and it MIGHT be fine the next morning.

 

[starr]

anybody?

 

[starr]

BUMP

 

[starr]

okay, i refuse to believe that there's no one out there that has had a similar problem, or knows what this could be.

 

[ivanr4g63]

it don't seems like your maft setup its causing this... sounds more like you may need to clean your throtle body... have you tried this? Mopar Combustion Chamber Cleaner (MCCC) seems to work great but any other Carburator cleaner will do the job
also check your accelerator cable that its not sticking, spray some WD-40 around the throtle body where the throtle body plate bracket meets the cable, all over the outside area where the spring is...

any improvements?

 

[starr]

okay after a couple weeks of this, and paying close attention this is what i have noticed. the high idle is directly connected with stop and go/city driving. if i have a high idle, and go out on the highway and drive a few miles at 70 or 80, when i come to my next stop my idle will be lower. (1-2k). if i have to go through a town, and go through a lot of stop signs, or lights, my rpm's will climb untill they'll get about to the 3k to 4k range. shutting the car off will not help. i shut it off, and when i restart it, it is high again immediatley, unless i go and run the car for 5 to 10 miles at 70 or 80mph. i noticed this because the other day i drove my car to work, highway all the way there and it was great. i'd come to a stop and be idleing nicely. then that night i went to the track and had to drive through a town to get to the track and my idle was at like 3500rpms. then of course as i was stageing, (lots of starting the car, driving 100 ft, then stopping, shutting the car off, then doing it all over again,) the rpms stayed at 3500 ALL NIGHT LONG!! of course untill i left the track and drove home on the highway. THIS SUCKS!! ever tried to launch a fwd car when you idle at 35k? it's hard! my times sucked. anybody got any idea on this? any help please? now that i know a little more about the problem, and have it pinpointed a little more i'm hoping someone will have an idea. thanks in advance.

 

[starr]

yep.

 

[starr]

anybody

 

[rabidfox]

just to throw something at you, I had a similar problem, although not as high an idle. I let the car warm up out of the closed loop(3-5 mins after temp gauge was full, it was winter) thn I just adjusted the BISS. That seemed to be it, I geuss motor mount inserts and a 3" exhaust rattled it loose, hope thats the problem...might not be but it may help

 

[gs-tclipse]

dude i have the exact same problme and cant fix it does your car ever do the opposite too like real low idle like wanting to stall or sounds like its running on 3 cylinders and its not my plugs or wires both brand new

 

[abakja1]

Possibly a IAC/ISC problem? Im going thru the same thing and there is a checklist to go thru if you may think your car fits this problem/description.

Check the VFAQ on "idle surge" or here at DSMTuners,..you may find some similiarities with your problems,..

Kevin

 

[iwon]

Damn, bumpin' this thread like coke.

Anyway, have you had your car tested for a vacuum leak?
It seems like it's either a fuel, vacuum or a throttle body problem since periods of time when the engine is constantly under acceleration it seems to go back to normal. Clean the throttle body and TPS, play with the BISS and get back to us.

 

[starr]

yeah i dont think its vacuum related because i got hella good vacuum. when i 'm driving down the road and let off the gas i got 25 vacuum. at idle i have 20. so i think thats really good. but i'm leaning more towards the throttle body being diryty, stuck, whatever, so i'll remove it and clean it this weekend and let you know. thanks.

 

[starr]

okay. it's fixed. not sure what fixed it but i took the t.b. off, cleaned it, re adjusted the t.p.s., and gave myself a little more slack on the throttle cable, and tightend the biss all the way in. now it still fluctuates with the idle from 750 to 1000 rpms, but i can live with that, sure beats 3500rpm!!!! thanks for all your suggestions. hope this post helps someone else.

 

[abakja1]

Happy that you got your car running again with something that you can live with,..

Sounds like you fixed the idle problem "enough" to live with, but not really "solved" the problem of idle surge,...I hope that it wont come back to such a high idle like at 3500rpms,.

My problem is the same as your sort of and I can "lower" the idle fluctuation point by adjusting the BISS screw all the way in (to 1000rpms), but my cold startup idle would hardly get the car going (would die cause of BISS all the way in and idle at less thatn 700 rpms),..But once its is warmed up and the idle surges begins, it would idle between 1000 to 1200rpms,...better than at 2000-2300 rpms when BISS is adjusted correctly (cold start idle at 800rpms).

The adjustment of the throttle cable would solve the idle surge, if that was the cause, as well as a mis-adjusted or dirty TPS and TB,...

I just hope that your car will "behave" from now on for you and not idle surge badly anymore,..

As for me, I tried all the above, but would rather get my car running "correctly". Im waiting on another TB with TPS and ISC and hopefully that will cure my problems (gone thru 2 TBs and 3 ISCs already with no seal leaks on TB,..possible it is the TPS as I switched from a early 90 TB to later May 90 TB thus had to solder in different TPS cable,..)

good luck
Kevin