Variable Idle

[00 Agent]

I did a search and couldn't find an answer.

Sometimes my car idles perfect, and sometimes it idles at 1500-2000rpms. It doesn't surge or dip or anything. What could cause this?

 

[Amodeo]

Check your throttle position sensor. I had the same problem and that's what it turned out to be.

 

[00 Agent]

According to my SAFC the TPS is good - 0v at closed throttle 5v at WOT.

 

[00 Agent]

btt

 

[00 Agent]

Ok, I have checked the TPS, throttle cables & plate, removed and cleaned ISC and tested it with a multimeter, checked the BISS and cleaned the TB. What's next?

 

[Amodeo]

Are you sure you don't have any vacuum leaks?

The tool described under "How to build an Intercooler Pipe Pressure Leak Tester" can be used to find vacuum leaks as well by pessurizing the intake system. Find it at

http://www.vfaq.com/index-main.html

 

[00 Agent]

Ok, I've checked and don't have any vacuum leaks. I've also done the vacuum reroute according to the info at taboo speed shop. Any other ideas on what it could be? I'm running out of possibilities here...

 

[laserblue]

You say 'sometimes'. When is 'sometimes'? Does it follow any pattern... like in the middle of a hot day, or after the car has been running for a while, or ????
This may sound dumb, but it happened to me: My idle would get fast [without surge] on a very hot day. It turns out that the throttle cable became too tight [no play] ONLY when the outside temp was very hot. The fix was to adjust the cable when the car was very hot.
If you can push the throttle plate lever closed with your fingers and make the idle drop, then you may have the same problem that I had.
It doesn't make sense that it's an air leak because the ECU would try to drop the idle and you'd get that annoying idle surge that we all have experienced at one time or another. Surge will only happen when the throttle lever is resting on that switch thingy. If the lever is not returning all the way, then the switch will not activate, and the idle will stay high without the ECU trying to knock it down.
Let us know what you find!!!!!!!!!

 

[00 Agent]

I can't find a pattern to it at all; it doesn't matter if it's hot or cold or how long it's been running or anything consistenst. I've checked the throttle cables and butterfly valve position and it does always close all the way. This is driving me nuts...

 

[00 Agent]

The car's still acting up. Here's a list of everything I've done/checked:

TPS - good
Throttle plate and cables - good (and clean)
EGR - blocked off
FIAV - blocked off
vacuum line reroute (taboo speed shop)
Tested (and cleaned) ISC with multimeter - good

What the hell else could it be?

 

[BitAddict]

have u checked your air sensor?(prolly not it but worth a shot) also the O2 sensor to make sure its working and grounded securely? good luck!

 

[00 Agent]

By air sensor I assume you mean the MAS? I can swap it out with my brother's to see if that's the problem. O2 sensor and gnd are good.