Chicken or the egg? Maf live data

[daveinfl33777]

Chasing a rough idle. Shakes especially when I first start it and seems to be worse in park/neutral vs in drive for whatever reason too...

It also surges. Will idle steady at 700 rpms for a while and then all of a sudden will pop up to 750rpms and then come right back down....what I notice is when this RPM goes up the MAF reading foes up from .6lbs/min to .9lbs/min....is the MAF reading incorrectly? Is the IAC opening on its own more and that is actually causing more air flow and that is why the MAF is reading more? I'm trying to see who to point the finger at. It is a case of the chicken and the egg what came first? I don't have data on the IAC. If I could see that the IAC didn't move and the throttle body didn't move (which I know it didn't cause I do have that data) then I can point the finger at the MAF giving a faulty reading and causing the surge....

 

[PSKSAM2]

Just a thought, before you go too deep on the MAF or IAC, but maybe a failing Throttle Position Sensor (TPS) blipping the throttle?

 

[daveinfl33777]

Well I did monitor TPS and it sits at 19.2% at idle and then sometimes goes to 19.6% and then back to 19.2%....I will try to monitor this again and see if the RPMS go up at same time the TPS blips to 19.6%

 

[PSKSAM2]

Good post by wmburns in this thread: Idle problems
He also covers cleaning the MAF and IACs.

He notes that the stability is most important and per the Ford manual a TPS variation of 0.05V is significant. I would think if you are seeing a jump of 0.4% (19.6%-19.2%), it is possible you may be in that range (5V*0.4%=0.02V) depending on how your fast your reader can read/display. Can't say I've ever watched my readings before.