High Idle questions

[Jason2215]

Ever since we've had the car (about 25k miles or so) it has idled pretty high. I never really paid much attention but lately I started making mental notes of everything it's doing...

When you start the car (this is cold, warm, hot) it shoots right up to about 2700rpm, then after about 3 seconds, comes down to 1500rpm. It stays in the 1200-1500 range (kind of surging back and forth) for as long as you'll let it idle.

Now, I've checked every single vacuum line and sprayed soapy water around every gasket. Nothing. Is there ANYTHING you guys can think of that I can check?

Oh, no codes.

Thank you in advance! Let me know if I can give more info...it's a 97 420a

 

[link16]

Check and see how tight your throttle cable is, it might be too tight. Clean your throttle body, and check your IAC, but I have never had a problem with my IAC.

 

[Jason2215]

Thank you....I did clean the IAC and the throttle body...have you ever had a problem with the cable being too tight? That seems really odd, but I guess you never know!

 

[roni-wan]

Yeah, clean the TB i had the same problem, cleaning it helped

 

[4UH8ERS]

Don't forget to check the PCV valve and lines. The valve itself and the hose tend to get cracks and are easily overlooked.

 

[92dsmtalon]

Does it even do it when u turn the idle screw down? If it does, then its ###### ## IAC, b/c mine kinda does the same thing, but mine was the opposite, mine was really low, and it just happend all of a sudden. So, ###### change out the IAC and should be good.

 

[Locke]

Does it even do it when u turn the idle screw down? If it does, then its ###### ## IAC, b/c mine kinda does the same thing, but mine was the opposite, mine was really low, and it just happend all of a sudden. So, ###### change out the IAC and should be good.

Remember where you are posting. 2gnt's don't have a BISS.

 

[Jason2215]

Thanks guys...yeah, i checked the PCV, but i went down and got a new pcv anyway, just to make sure, they're cheap. I haven't put it in yet, been at work all day. But I'll see how that works out. I was thinking it could be the Idle speed sensor...the one on the throttle body? Anyway, maybe it's sticking...I'll have to check that.

If you are on a level road, the car will accelerate itself all the way up into 3rd/4th gear depending on how long you let it go. I mean, it's really slow, but still...something's a bit off here...

 

[link16]

try and swap out your TB I have a problem with my TB right now but I am just going to swap it.

 

[VelocitàPaola]

I doubt the TB itself is bad... possibly the TPS. My TPS went bad once; it caused noticeable idle surge.

 

[Jason2215]

Velocita...

When you say it caused idle surge, what exactly, and when did it occur? Mine stays pretty steady, it's just higher. I think i'll give that a shot, it's worth a try.

 

[VelocitàPaola]

I never noticed a clear pattern as to when it appeared; it happened when the car was cold, hot, whatever. When it was surging, the RPMs stayed higher than what idle should be: probably anywhere from 1500-2500RPMs. I changed the TPS so long ago, I don't really remember where exactly it surged to.

 

[Jason2215]

That just sounds like what mine is doing. Idling too high, surges between 1200 and 1700 rpm while in park, etc. Maybe we're on to something!

 

[Shadow98]

Yeah, that sounds like the TPS. When mine went out it would mostly surge when my motor was warm.

 

[VelocitàPaola]

Yeah... I've got a spare TPS sitting around, but unfortunately it's my old one, so it won't do you any good. Look for one on eBay, or from someone who's parting out a car on 2GNT.

 

[eclipsepunx]

I know this is an old thread but it's a common problem and i think i can help if anyone comes across this looking for answers. TPS did fix a lot of my surge and after replacing, my vacuum sat steady at 15. Being a perfectionist I wanted it at 20 where it's supposed to be. Took me forever to figure it out but people should check their torque on their manifold bolts. After tightening mine, and using some thread lock, it took my idle from 2100 to 1100. Now my only beef is after revving the rpms drop really slow....

 

[Carter_95RS]

my throttle is really slow at coming down too, but i have a moddified jeep tb, spring isnt very tight, i usually just put my foot behind the petal and pull it lightly and it drops

 

[VelocitàPaola]

I know this is an old thread but it's a common problem and i think i can help if anyone comes across this looking for answers. TPS did fix a lot of my surge and after replacing, my vacuum sat steady at 15. Being a perfectionist I wanted it at 20 where it's supposed to be. Took me forever to figure it out but people should check their torque on their manifold bolts. After tightening mine, and using some thread lock, it took my idle from 2100 to 1100. Now my only beef is after revving the rpms drop really slow....

It sounds like you still have a vacuum leak somewhere. I wouldn't say 15 inHg of vacuum is bad; generally between 15 and 20 is acceptable. At idle your RPM's should be around 800-900, though.

 

[eclipsepunx]

Right...is the soap technique worth giving a shot or should I spend the few bucks to replace the lines? Pulling up my pedal works as well but it still won't drop to 700..I'll look at it today and post back

 

[Locke]

If pulling up your pedal helps, then your throttle isn't closing completely on it's own.