Trying to help my sister out with her car. Its a 97 hatch. D16y7.

She has been having a crazy idle surge for about a year now. It revs between 1k and 2k constantly. Sometimes she will even get a surge while driving??

I tried to flash codes. Couldn't get anything. Turns out the previous owner had put the wrong ecu in (auto instead of manual) and pulled the cel bulb. So i fixed that, threw in an ecu I had layin around. And then I had a CEL for IACV. So i figured I would change that, and all would be good. I found a used one, swapped it, no more code. But still has the crazy surge?? After messing around a bit I figured out that if I unplug the MAP sensor the surge goes away and it idles nice, but high (1200ish). Just playing around I unplugged TPS as well and it idles beautiful. So she is just driving it as is for now. I tried swapping the IACV, MAP, and the whole TB. And its still there.

If i unplug vacuum hose to brake booster, It revs way up, and it seems there is lots of vacuum. Plug it with my finger and it just surges again.

Im at a loss??? Someone make a suggestion. I would imagine its something easy that I am overlooking. But im frustrated and dont know what to do.

 

no ideas?

 

Vacuum leak.

 

agreed^^. Look for dry rotted vacuum lines and listen for hissing... Or hook up a vacuum guage and look for fluctuations.

 

Thats what im leaning towards. Looking @ everything, I cant see or hear any issue.

I need to put a set of rings in it, cause its using oil pretty bad. So i think Ill do that and while the motors out I will investigate all the hoses etc. further.

 

You could check for vacuum leaks by attaching a rubber hose to a propane tank and spraying it around possible leak areas and listen for a change in idle. Possibly hoses...check brake booster lines...check tb and I.M gaskets.

But don't overlook the possibility of a stuck fast idle thermal valve. I had a civic that would surge ONLY AFTER the engine started to warm up and this ended up being the culprit because it too can be the source of a vacuum leak if you can't find anything obvious with the hoses.

1)Start the car and disconnect the intake or whatevers connected to the throttle body. Look inside and there should be two holes along the left side. The upper hole leads to the IACV and the lower port leads to the fitv.

2) Now the fitv has a wax plunger inside that as it heats up SHOULD slowly begin to close which transitions your cars idle from higher (more fuel, when starting) to lower (when warming up). Now sometimes these can go bad (thermostat generally goes bad from poor servicing of coolant) and what happens is they don't close off completely which means it will continue to draw in excess air on top of what is being drawn in by the iacv which will cause your idle to jump up to whatever, ecu hits fuel cut, jumps to whatever, ecu hits fuel cut, etc.

3) Once the idle surge begins put your thumb over the lower port in the t.b. There should be no suction at all from the lower port once the engine is warmed up. If there is, you know you have found your vacuum leak. Also, check the cover plate on the back side of the fitv. The guy who owned the car before me didn't bolt it down but hand tight and the cover plate came off drawing in air.

You can generally fix these by removing it and screwing in the beeswax plunger back and than backing it out about a turn. But I ended up getting a skunk2 tb which doesn't have a spot for the fitv to solve my problem.

Sorry for being long but these idle problems can be a real bitch.