fluctuating idle only when warmed up
#1
Instructor
Thread Starter
Join Date: Nov 2003
Location: S.F Bay area
Posts: 137
Likes: 0
Received 0 Likes
on
0 Posts
fluctuating idle only when warmed up
I have done a seach on this but I only found problems of fluctuating idle when cold/start-up.
My car starts fine and when the engine temp hits a certain level (not sure exactly, but around 170-180) the idle starts to fluctuate. It slowly rises to about 1500 rpm then drops back down to a normal idle. Then slowly it rises back up to about 1500 rpm or so then drops back down to a normal idle.
This only happens AFTER the engine warms up.....
Start up and cold idle is fine....
Also, I already checked the TPS sensor, its OK,
I assume the idle stablizer valve is fine since it only happens AFTER the engine is warm.
O2 sensor is fine.
That just leaves the DME temp sensor...
Thanks for the help....
My car starts fine and when the engine temp hits a certain level (not sure exactly, but around 170-180) the idle starts to fluctuate. It slowly rises to about 1500 rpm then drops back down to a normal idle. Then slowly it rises back up to about 1500 rpm or so then drops back down to a normal idle.
This only happens AFTER the engine warms up.....
Start up and cold idle is fine....
Also, I already checked the TPS sensor, its OK,
I assume the idle stablizer valve is fine since it only happens AFTER the engine is warm.
O2 sensor is fine.
That just leaves the DME temp sensor...
Thanks for the help....
#2
Does the same thing happen with the O2 Sensor disconnected? Have you tried changing the idle speed by openning up the idle screw on top of th throttle body to see if that has an effect and keeps it from changing after warming up.? Have you tried blocking off the line from the idle stablizer to the intake to see if the idle is still changing? Those are the things I'd try to at least to find out what effects the idle then you could at least start to figure out what's causing it.
Brent
Brent
#3
Rennlist Member
Originally Posted by Brent951
disconnected? Have you tried changing the idle speed by opening up the idle screw on top of th throttle body to see if that has an effect and keeps it from changing after warming up?
Sounds like opening the idle screw just a tad (counter clockwise) would help.
Of course, this is a "quick fix." The correct way to reset the idle is bypassing the ISV with a jumper wire to the ports in the diagnostic socket. Do a search for the exact ports.
#4
Instructor
Join Date: Mar 2005
Location: Long Island NY
Posts: 135
Likes: 0
Received 0 Likes
on
0 Posts
I have the same fluctuating idle on my 1985 944. but my car idles a little above 1000 rpm which I think is a little high. Would opening up the idle screw speed up the idle rpms? I'll try the troubleshooting tips anyway. Thanx and good luck vetblack
#6
Rennlist Member
Originally Posted by Drifting STi
I have the same fluctuating idle on my 1985 944. but my car idles a little above 1000 rpm which I think is a little high. Would opening up the idle screw speed up the idle rpms? I'll try the troubleshooting tips anyway. Thanx and good luck vetblack
Adjust it in tiny increments until the rpm needle sits right at 900, a notch below the 1 mark.
#7
Instructor
Thread Starter
Join Date: Nov 2003
Location: S.F Bay area
Posts: 137
Likes: 0
Received 0 Likes
on
0 Posts
It was a bad ISV !!!!!!! It was stuck open so when I started the car, it fired right up and maintianed a high idle. Once it warmed up, the DME was adjusting A/F misture to compenstate and it kicked in and out of the idle mode. I disconnected the ISV (plugged both ends) and that solved the problem, I had to turn up the idle screw a little (not the air srcrew on top of the throttle body), then readjust the TPS to match the idle adjustment.....
But now it works just like it should......
But now it works just like it should......
Trending Topics
#8
Instructor
Join Date: Mar 2005
Location: Long Island NY
Posts: 135
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Luis de Prat
In your case, the idle screw may be open a bit too much. I would try closing it slightly (clockwise). It's located on top of the throttle body.
Adjust it in tiny increments until the rpm needle sits right at 900, a notch below the 1 mark.
Adjust it in tiny increments until the rpm needle sits right at 900, a notch below the 1 mark.
#9
Pro
Join Date: Sep 2002
Location: Blacksburg, VA & Northern VA
Posts: 629
Likes: 0
Received 0 Likes
on
0 Posts
how exactly does the ISV function? When doing a delete, do you have to make any adjustments to the ecu to fool it into thinking it's still there or anything?
#11
it's below the intake manifold it's T shaped and has a wire and a connector on the top of it. It's diffcult to see and get to without removing the intake manifold. It should be sitting between runners 2 and 3.
Brent
Brent