high idle

[XfireZ51]

Jarek,

So after you swapped IAC, you say that it idled fine until you drove it? Did you go thru the IAC reset procedure? Any chance you could scan during your drive?

[Jarek5_7]

yes it idles fine until driven. I swapped the iac and tried to reset it as in the book I have. its " corvette fuel injection and electronic management" by charles o. probst. it covers many efi on corvettes also zr1. its written there to press accelerator pedal a little and start the car for 5 sec then turn off the ignition for 10 seconds. I did that and havent notices any change. but now I see that its also written there that the reseting of iac is needed after unpliging the iac while engine is runing. I didnt unplug it on engine runing.
I will do that tommorow and then the reset procedure. Or I should reset it a diffrent way? also I will try to scan the car while driving tommorrow.

I really want to get this car into a good condition and high idle is I think the most annoying issue in it.

So far I changed for new injectors, plenum and tb gaskets, coils, wires, plugs, checked for vacuum leaks, havent found any yet.
( sec vacuum pump is working and sec vacuum system holds vacuum good, also the actuators hold vac and works good, the primary vacuum reservoir hold vac, I check also vac on the other side in the hose going to plenum it also holds vac)

[Jarek5_7]

if after I drive the car the ecm wants to have good idle rpm like 650 but engine idles high, its a vacuum leak for sure right?

maybe some egr valve or something is turn on and it leaks vacuum after a drive?

[Nick]

Marc Haibeck makes several adjustments to the linkage and replaces the dag with a spray-on compound. He fixed my high idle TB and its been great for several thousand miles and several years. Once you have sorted out all of the other potential issues (and it sounds like you have), I'd give him a call and see what he says.

[WydGlydJim]

Just a note. The 90s are notorious for having a slow return to idle. I've read it can take up to 30 seconds. This is an eternity, if you have ever clocked it. Plus the idle will not come all the way down while the car is rolling, even if the clutch is in and off the gas. Just making sure you are not chasing a problem that is not there. Many people complained about this issued, and a new prom was calibrated. Mine will come down, but sometimes at a light, it will not come down all the way, before the light changes.

[WB9MCW]

Originally Posted by WydGlydJim

Just a note. The 90s are notorious for having a slow return to idle. I've read it can take up to 30 seconds. This is an eternity, if you have ever clocked it. Plus the idle will not come all the way down while the car is rolling, even if the clutch is in and off the gas. Just making sure you are not chasing a problem that is not there. Many people complained about this issued, and a new prom was calibrated. Mine will come down, but sometimes at a light, it will not come down all the way, before the light changes.

Marc Haibeck makes several adjustments to the linkage and replaces the dag with a spray-on compound. He fixed my high idle TB and its been great for several thousand miles and several years. Once you have sorted out all of the other potential issues (and it sounds like you have), I'd give him a call and see what he says.

Now I see why you have the other post ging for where to get a stock prom --- As you will see in my answer to you on that thread ---HAIBECK is the man for the chips!!!

[Jarek5_7]

can anyone post here a vacuum routing schematics?

I found only this one http://www.zr1netregistry.com/gifs/vacuum.jpg

but I cant see for example where secondary map should be conected ?

[tomtom72]

The part labeled Vacuum differential sensor is the part we all call the secondary MAP sensor. The hose feeding it comes out of the left side of the plenum between the front four & rear four runners, if I remember correctly. That MAP is bolted under the bracket that the ECM and cruise control diaphram is mounted on, just on top of the battery.


Tom

[Jarek5_7]

I thought ith was the differential sensor but I got confused because I was looking for a sensor with two inlets. differencial as for measuring difrence in pressures. mine isnt connected to anything :/

[WB9MCW]

Originally Posted by tomtom72

The part labeled Vacuum differential sensor is the part we all call the secondary MAP sensor. The hose feeding it comes out of the left side of the plenum between the front four & rear four runners, if I remember correctly. That MAP is bolted under the bracket that the ECM and cruise control diaphram is mounted on, just on top of the battery.


Tom

And often a backfire will blow that MAP hose loose causing a high idle