car idles too high
11-28-2006, 12:59 AM
#1
Drifting
Thread Starter
car idles too high
I noticed this the past couple of days. When I start the motor it will idle at around 900 rpm (which is correct) for a few minutes, then it will go up to 1100 or 1200 rpm and stay there for idle.
Now when I drive and I usually go up to 4000-5000 rpm between shifts and when I come to a stop the revs come down pretty slow and sometimes it stays at around 1800 -2000 rpm for a little while or until I start moving the car with the clutch (no gas) and it'll bring the revs back to the 1100-1200 idle.
what is the most likely cause of this? I thought maybe vacuum leak as a removed the airbox and some connection to it when I did my belts/ water pump but I made sure everthing was back on and tight. Also the idle isn't jumping around or anything it's pretty steady at 1100 rpm and the second symptom is sometimes when i higher the idle will come down to 2000 rpm and then very slowly comes back down to 1200.
any ideas? the motor still runs great but when it's idling high it will obviously use more gas and it's pretty loud. My mechanic noted that the car was running rich when I went in to adjust my timing belt.
Now when I drive and I usually go up to 4000-5000 rpm between shifts and when I come to a stop the revs come down pretty slow and sometimes it stays at around 1800 -2000 rpm for a little while or until I start moving the car with the clutch (no gas) and it'll bring the revs back to the 1100-1200 idle.
what is the most likely cause of this? I thought maybe vacuum leak as a removed the airbox and some connection to it when I did my belts/ water pump but I made sure everthing was back on and tight. Also the idle isn't jumping around or anything it's pretty steady at 1100 rpm and the second symptom is sometimes when i higher the idle will come down to 2000 rpm and then very slowly comes back down to 1200.
any ideas? the motor still runs great but when it's idling high it will obviously use more gas and it's pretty loud. My mechanic noted that the car was running rich when I went in to adjust my timing belt.
11-28-2006, 03:07 PM
#4
Rennlist Member
my tach reads 1100 at idle.
When i went in for inspection, the machine read 900. My tach is just off by 200.
Doesnt sound like your case tho.... LOL Does your TPS still click?
OH WAIT!
It could be as simple as... well... Is your throttle return spring still there?
Mine used to do the same thing, then I looked on the throttle body to notice the very apparent lack of a spring. HAHA
When i went in for inspection, the machine read 900. My tach is just off by 200.
Doesnt sound like your case tho.... LOL Does your TPS still click?
OH WAIT!
It could be as simple as... well... Is your throttle return spring still there?
Mine used to do the same thing, then I looked on the throttle body to notice the very apparent lack of a spring. HAHA
11-28-2006, 07:27 PM
#5
Addict
Rennlist Member
Rennlist Member
Defintely check for vacuum leaks!
Physically check all the connections. Those old rubber connectors should be tie-wrapped to make sure they are snug.
Failing anything obvious, to check for leaks, take a spray bottle and mist water around places where vacuum leaks can occur, like intake, vac hoses, air box, J-boot, etc. If you've got a leak, the idle will drop when it draws in the water. Some guys use carb cleaner, in which case the idle goes up, but you've got to be a little careful where you spray it!
If you do the latter, have an extinguisher handy, eh?
Physically check all the connections. Those old rubber connectors should be tie-wrapped to make sure they are snug.
Failing anything obvious, to check for leaks, take a spray bottle and mist water around places where vacuum leaks can occur, like intake, vac hoses, air box, J-boot, etc. If you've got a leak, the idle will drop when it draws in the water. Some guys use carb cleaner, in which case the idle goes up, but you've got to be a little careful where you spray it!
If you do the latter, have an extinguisher handy, eh?
11-29-2006, 09:52 PM
#6
Rennlist Member
I have heard that adjusting the throttle is more in depth than you think....and could possibly be the culprit.
The thing is, wouldn't a leak allow the car to fluctuate at idle? Mine sits steady....and tends to rise even just a bit. Hmmmm.......
The thing is, wouldn't a leak allow the car to fluctuate at idle? Mine sits steady....and tends to rise even just a bit. Hmmmm.......
12-01-2006, 01:03 AM
#7
Three Wheelin'
I had the same problem on my NA and turned out to be a clogged Idle Speed Valve. I heard you can clean them with brake cleaner but dont quote me on it. You do have to remove the manifold to replace or service.
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12-01-2006, 07:34 PM
#9
Nordschleife Master
Will, you are correct. The ISV is under the intake manifold, has a black connector coming out of the top, and two vacuum hoses coming out each side. Its a cylinder shape is cadmium plated i think (has the hard to miss yellowish / gold finish). If you want to get technical about it though.. the bracket is connected to the block 
.
Its a pain in the butt to change because the intake manifold and fuel rail need to come off the top end in order to reach it. If you are having wandering or high idle issues, it may be a good idea to either clean it out or change it. Cleaning it seems to work for everyone, but i personally felt if i was going through the trouble to remove a good portion of the top end of the engine, i was just going to remove any doubt and change the ething.
With the intake off, its a great time to address alot of the small things that cause running issues. You will have easy access to the vacuum hoses and lines, heater control valve, bell housing grounds and can change the two o-rings on the air/oil seperator.
.Its a pain in the butt to change because the intake manifold and fuel rail need to come off the top end in order to reach it. If you are having wandering or high idle issues, it may be a good idea to either clean it out or change it. Cleaning it seems to work for everyone, but i personally felt if i was going through the trouble to remove a good portion of the top end of the engine, i was just going to remove any doubt and change the ething.
With the intake off, its a great time to address alot of the small things that cause running issues. You will have easy access to the vacuum hoses and lines, heater control valve, bell housing grounds and can change the two o-rings on the air/oil seperator.
12-02-2006, 02:50 AM
#14
Addict
Rennlist Member
Rennlist Member
TPS, been there , done that, lol.
There's a signal in and two signal outs. one for idle position and one for WOT. No signal defaults to mid throttle maps. Unplugging it should show no effect on a bad sensor. The idle will rise on a good one. High idle and slow return to idle are normally the syptoms. Also, for cars with O2 monitors or if you'd like to hook a multi meter to the O2, revving it and watching the monitor. when the RPMs are above 1100 for late cars and 800 for early and it is in the idle position it should fall off the lean side or all the way off the map. If the meter is showing dithering on decel above 1100, it is not seeing the idle position. Good luck, HTH
There's a signal in and two signal outs. one for idle position and one for WOT. No signal defaults to mid throttle maps. Unplugging it should show no effect on a bad sensor. The idle will rise on a good one. High idle and slow return to idle are normally the syptoms. Also, for cars with O2 monitors or if you'd like to hook a multi meter to the O2, revving it and watching the monitor. when the RPMs are above 1100 for late cars and 800 for early and it is in the idle position it should fall off the lean side or all the way off the map. If the meter is showing dithering on decel above 1100, it is not seeing the idle position. Good luck, HTH