Today while I was stopped my idle dropped for a couple seconds. I put it in park and it moved back up. My idle sits at the halfway notch between 0 and 1000. I dont know if that notch is 500 or what but the needle dropped just below the first notch (250?). I have had this surging idle issue for a while where it sits just below the middle (500?) and moves just a little up and down. I do not have a CEL on right now so I dont know if any codes are being thrown but I assume no. I have a new IAC, TPS, Alternator, temp sensor and oil pressure sending unit. It seems like sensors are going out one at time. I read that a failing O2 sensor would cause high idle and a failing MAP would cause low idle. I know I need to get the compression tested and fuel pressure tested but I was hoping someone would have had this experience and give me some ideas until I can get it in a shop or get a pressure kit and test it myself.

 

Did you thoroughly clean your throttle body yet? I would do so as that itself can create some strange idle symptoms.

I would also "freshen" all of your engine grounds. They can be responsible for many gremlins and grounds are so very often overlooked.

I'd start with those two things and then see where you are at............

 

Pulled the TB earlier this year when I installed the new IAC and TPS. Cleaned it up by hand. I have not taken it apart in a few months so I have no idea but It should not be bad after only a few months. I plan on doing a fuel pressure test in the next couple of days if I last that long. If the fuel pressure is fine then I would suspect either the MAP or O2. I hoped someone would have had similar issues and posted their results. I tried to search but there are so many posts that people do not follow up on and post their solutions for results..... very frustrating when you find a post where someone seemed to have the exact same problem but never posted the rusults.