I have a 91 civic std that currently has the stock dpfi d15 in it. When I first start it up, it idles fine, but a minute or so later once it warms up it starts idling very irratically. Just up and down, now its not an extreme high rev, and i dont have a tach to tell exactly how far its going, but by my guess from how it sounds, id say its just jumping from idle, up about 750 rpm and back just over and over again. When in gear, its good and steady, but in neutral it idles all over the place as said above. I've cleaned out the iacv, cause i heard thats a common issue, but that did nothing for me. Ive tried the idle adjust screw and it does absolutely NOTHING. My first thought is maybe its the TPS but I havent had a chance to work on it yet. Anybody else got any ideas? Im a complete newb to these motors, so ill take any and all advice ya got lol.

 

You do realize that sensor operates off of coolant right?

Have you bled the cooling system / Have you checked your coolant level?

Checking it is more involved than just looking at the resivoir...

 

Nope, havent looked into that really. Are you talking about the iacv when you say it works on coolant?

 

Yes the Idle Air Control Valve has coolant lines going to it - are you sure you cleaned the IACV?

 

Yea thats what i cleaned im sure of that lol, i was just confused cause you said that sensor is coolant controlled and i asked about the TPS possibly being the issue so i was a lil confused till i remembered i mentioned cleaning the iacv. But yea, i cleaned that out bout a month ago, all fluids were good when i did that. All fairly new and clean still and the levels were good.

I do not currently have a check engine light, but a day or two after cleaning the iacv, i had a CEL throwing a code 7 which is TPS if i remember, but my battery crapped out on me so i replaced it and the code cleared and hasnt came back.

 

Well then get a multi-meter and see what your voltages are - then go through the range and look for dead spots.