98 monte 3.1 starts and idles fine, but after driving for awhile the idle will go up then down to almost stalling. Don't notice when sitting in drive, only when in park - maybe a little when in drive. Also, doesn't do it all the time, but it is getting more frequent?

If I give it a little gas it will usually return to normal.

I was going to start with the fuel and air filters - what do you think?

Thank you for any help!

 

By chance is it throwing any check engine codes?

I'm thinking start with checking for vacuum leaks.
May also want to pull the IAC off and clean it of any carbon-ish gunk. Might also be a good time to pop the throttle body off and also clean it up.

Next, I'm curious, how many miles are on the spark plugs?

If regular maintenance has not been done, the link below might be a good read:
https://montecarloforum.com/forum/ge...0-miles-46078/

 

Definitely clean the tb and the maf / iac for right now

 

Thanks for the help guys. I will get started on the cleaning and let you know how it goes. I bought the car used about a year ago and haven't had any real issues with it. It has about 120,000 on it now.

I just found the gas filter to be connected with a rubber hose and it was loose, so I tighten and haven't noticed the problem return, but that doesn't mean it won't - it comes and goes.

Thanks again.

 

Hi BillyBob, to MCF!
Just to add to what Mike and Jason said, if you haven't done a tune up in a while I Also recommend changing your PCV valve. It is part of regular maintainance and could Also cause your problem because one end of it is connected to a vacuum line.

 

Good find, it might have been sucking air in with the fuel.

Regardless, go through the link I provided of services to check at 100,000 miles. Sure, you are 20K over that mile stone, but it's NOT too late to still do some good maintenance so she'll last long and hopefully problem free.