: wierd idle

03-03-04, 08:23 PM
i have a slight problem i cant fix, the idle seems to jump around a bit when its in drive and idling and i know there are alot of posts about similar problems and i have read them and it leads me to believe its a vacume leak but i cant find one anywere (trottle body, intake) is there anything im missing my trottle body is clean so it cant be that i just cant figure it out and its realy noticable not just a slight rough idle if there is anything i am missing or anything else it can be your input would be greatly aprieciated thank you

p.s. its a 97 sts if that helps

03-03-04, 08:40 PM
So your saying the idle jumps (or hunts), meaning its not really rough (bumpy)...

This would lead me to believe a vacuum leak. Unless its really small, it would do this.....

THe best thing to do is get a big flash light (brightest possible), and spray WD-40 (or something with a mist), and when you get close to the leak, the engine speed should change... This will help you find where it is.

Use the vaccum line diagram on the underside of the hood to help you determine where it could be..... Spray in all those areas...

Another option is most decent have smoke machines.. What they did (and I did it with mine) is they hook a machine up to the plenum and it pressurizes it with smoke, and the smoke comes out of where the vacuum leak is.....

If its just bumpy but stable it could be other things, but if it hunts like you said Id say its a vacuum leak...

Also, did it just recently start (sudden) or has it gotten worse?

03-03-04, 08:49 PM
wow that was a fast reply thanks to answer the question it just started about a weak ago aa couple of weaks ago but it has just recently become more frequent

03-03-04, 08:53 PM
So do you think it complies with what I said?

My personal advice would be to take it to the shop. Ive tried the WD40 method and its marginal at best..... This takes 5 mins, and may not even charge you if they're not busy!

You mentioned the TB is clean, did you take some stuff apart to clean it???? Has ANYTHING been done recently to the engine??

03-03-04, 09:20 PM
My 98 Deville (109K) also has a rough idle at gear only (D or other), the rpm jumps from 575 to 650. I can feel the car vibrates. When I put it on Park or Neutral, the idle is fine (625-650). There is no code. Thr TB was cleaned. Could it be the transmission?

03-04-04, 08:43 AM
i do agree with you about the vacume leak that was my first thought i just wanted to see if it could be anything else because i cant find one. and the reason i know the trottle body is clean is because i thought that was my problem and it was real dirty but i bought new seals and nothing is leaking i guess my next step is to go to the shop .

thanks for all the fast replies

El Dobro
03-04-04, 07:58 PM
Have you cleaned the idle air control valve located on the side of the throttle body?