idle issues jumping up and down
 

I'm having a problem on a 93 civic d16z6. when first fired up cold or warm the car idles fine but after a few minutes or seconds (it varies) it starts to jump idle. I check all vacuum lines and everything is fine. check engine light is not on. when we unplug the iacv the idle quits jumping so we put a new iacv on it and it didn't change anything. Took the intake off and put my hand over the throttle body and the car wants to die which is good but when i do that you cannot hear any leaks or anything trying to suck in air anywhere else. just trying to troubleshoot what this can be. lets hear your opinions.

Re: idle issues jumping up and down
 

Check the MAP sensor signal voltage at as close to normal idle as you can.

Re: idle issues jumping up and down
 

could be your FITV that needs to be tightened

Re: idle issues jumping up and down
 

ok I will check both of those. I work on these things all the time but this one is just being a pain i've been over numerous things numberous times and still nothing.

Re: idle issues jumping up and down
 

Checking the MAP sensor voltage will show a problem with the FITV so you don't have to run two tests. Warm the car up to normal operating temperature before checking the MAP sensor.

Re: idle issues jumping up and down
 

Please enlighten me on this. I didn't know map voltage would show fitv problems. What does the voltage look like between a good and bad fitv?

Re: idle issues jumping up and down
 

The vacuum inside the IM decreases when the FITV lets extra air in the same way the vacuum decreases when the throttle lets more air in. If the FITV doesn't close all the way when the engine warms up, the vacuum inside the IM will be lower than normal and the MAP sensor signal will read higher than normal. Different types of motors often have different vacuum levels. Most motors discussed around here should have the MAP sensor signal read about .4-.7v at warm idle. Checking the MAP wouldn't pinpoint the problem to the FITV, but it would show a higher signal voltage if the FITV is currently causing any problems when the motor is warm. How much higher depends on how much extra air is getting into the manifold around the TB.

Re: idle issues jumping up and down
 

That's good info.

but my 2 cents... My car wasn't runnin weird or anything and I pulled of my FITV and it was loose anyway. You might just wanna pop it off real quick and tighten it for the hell of it. MIGHT fix your problem, might not. but at least you'll avoid having to do it later. lol

Re: idle issues jumping up and down
 

Thanks delsolproblems, good info.