Well, I've been messing with my 91 Accord since December last year upgrading various components. It all took a lot of work and ended up going well except there's one last issue that has been keeping me from driving the thing any further than my neighbor's driveway. In fact, it’s been taking me so long to figure this idle problem that I ended up buying another used car (2011 Outback with 133k). I still want to fix this idle issue with the 91 Accord so that I can sell it for a descent price. The idle issue is a surging high idle that takes place once engine has warmed up to operating temperature. I've asked and done all sorts of things to try to remedy the urging idle to no avail. Last night I tested the TPS to see if that might be an issue and this is what came of it: 0.46V idle and 4.51V at wide open throttle. I then proceeded to turn the engine and let it warm. Now, to initiate and sustain the surging idle I have to give it a bit of throttle action and that’s it. During the surging idle which goes on indefinitely, the TPS signal remained at idle value of 0.46V (yes I know it should be 0.50V, but that's close enough I think). By the way, the TPS ground is good and the supplied voltage is a perfect 5.0 so this rules out the TPS, right? Having said that, there was a brief blip of voltage loss from the TPS when opening butterfly at 4.0V and then again when closing the butterfly at 3.6V, but I do not see that as a problem since it takes a lot of butterfly opening to get to this “high voltage” readings and the butterfly should ever open that much anyways per my driving habits 😊

I checked PCV valve that I replaced from original about 4 years ago with a generic brand one, but it seems to work fine and has been for all those years. The PCV has a lot of suction at idle and my goodness there is so much high pulse air blowing out the PCV opening from the valve cover; I was surprised but perhaps that’s normal?

One interesting side note: When the car headlights are on you can count on the surging idle issue, otherwise the surging idle rarely happens (without the headlights on). So during daytime driving it's fine except that each time the throttle is released and allowed to go to idle it does so high at first theb settles to good idle rpm eventually.

This idle conumdrum is a real kick in the nuts.

Dave