fast idle after warms up

[southrneclipser]

I have a 95 rs with the 420a. Its mostly stock with only intake and exhuast. Stock fuel system. Deleted emissions and vacs.
It has new TPS and idle control valve.

I never had an idle problem until i changed the head gasket. I did not remove the intake manifold when i pulled the head off so i didn't replace the gaskets.

When i crank up the car it idles at 1200 rpm, but when it heats up it'll hang around 2000 rpm. I've sprayed carb cleaner all over the intake manifold and it didn't bring it down. I can't find any vacum leaks or anything like that. I can't figure out what it is. When i put my hand in front of the throttle body and cover it up, it will bring the idle down but the car still runs, so does this mean it's still sucking in air somewhere? Also when i pump the brake it will make the idle fluctuate up and down. So what could it be? Could i have a crack in the intake manifold or something that i haven't found?

 

[Doug99RS]

It could be any number of things but it does sound like a vacuum leak of some sort. I would recomend RE-checking any and all of these areas:
-Injector O-rings, give each injector a little twist while you're spraying with Carb Cleaner
-Intake Gasket, don't forget the underside of the manifold as well
-Cruise Control resevior (If applicable) located under the intake
-EGR Tube (If still attached), make sure you have the metal gasket where the valve meets the head as well as the paper gasket where the tube meets the intake
-Vacuum hoses, either capped off or properly attached. Large vacuum hose to the Brake Booster, small hose for evaporative emissions, cruise control, EGR valve small hose
-Check to make sure you don't have the throttle cable over-tightened. This will hold the throttle plate open.
-Debris at the plate, usually sucked in to the intake but you never know.
-A Bad Idle control motor or one that's not plugged in.

Those would be the things I would check for a high idle concern especially after the work you just mentioned.
Doug

 

[southrneclipser]

i'll have to check all that when i get home on tuesday. My egr is blocked off properly BTW. And i checked the throttle cable.

Some more info though that i don't think i mentioned:
When i'm on the gas and let off it, it will drop to about 900 but then climb back up the 2000. Also when the throttle plate is completely closed and i spray carb cleaner in it, you can see it get sucked past the throttle plate. And when i cover up the little hole where the idle control motor sucks in air, the idle does not change. But it will go down if i cover up the entire throttle opening. So i think a part of the throttle plate might have gotten chipped of or something. Just thought it might help to tell you guys. Thank you for all of the info

 

[Doug99RS]

Actually, that is pretty helpful and good that you noticed the differences in idle with the finger over the Idle bypass port. What this tells me is that the IAC is already shutting off the passage as much as it can but still is not able to affectively drop the RPM back to the target RPM of around 700-800RPM. If that passage was open at all then you would have heard the RPM drop and there would be a pretty serious suction on your finger. Also, slowly closing off the port and then rapidly removing it should cause a serious idle flair IF the vehicle were working perfect.

The Carb cleaner getting sucked in at the throttle plate is perfectly normal. If you were to remove the TB and hold it up to a light you'd still see that there is a small amount of light that gets by the plate. This is normal and frequently, we find cars stalling out that are all gummed up at that plate.

You should have someone help you by shutting off the car for you. With you under the hood, listen for a hissing noise as the engine shuts off. This can help you redirect your spraying technique to the area making the noise the longest after you shut the engine off.

 

[southrneclipser]

thank you so much for this info. I have not been able to find anyone to shed light on this subject. I will definately do these things as soon as i get home.

Is there any way that it could be a fuel problem? I was thinking that maybe it idles lower cold because thats when it's running richer. So when it heats up and leans out, the idle goes up. All the research i'v done has only talked about guys having idle problems when they install bigger fuel pumps. That's why i'm bringing it up, but my fuel system is all stock so i didn't think it would be affecting my idle. I don't know though.

 

[Doug99RS]

Air/Fuel ratio shouldn't have anything to do with this but throttle position sensor could affect idle and driveability issues. When a TPS starts acting up, it varies the voltage to the PCM and the computer can take these wrong readings and cause idle to change on it's own.

I still think your issue may be vacuum leak related. Are you getting a check engine light at all?

 

[southrneclipser]

yes the i forget the code but it said "target idle not reached"

that's the only thing its on for

 

[Doug99RS]

Ok, that's helpful to an extent. It tells us that the computer doesn't see any other problems i.e. no sensors are unplugged and that the computer is trying everything it can to bring the idle back down.

The way the computer works is that there is a set amount of airflow that goes around the throttle plate. The computer registers that airflow by monitoring MAP sensor voltage which it calculates in to a volume of air. If the computer wants more airflow in order to reach "target idle" then the IAC motor plunger is opened up wider thereby letting in more air. If the computer sees that too much air is getting in then it will close the plunger in to restrict extra airflow.

When the computer sees excessive or insufficient airflow and it has commanded this plunger to move all the way to one extreme and target idle STILL is not met then it turns on the check engine light and throws that fault code.

High idles are caused by throttle plates being stuck open, vacuum leaks or a bad IAC motor. You've verified the throttle is shut and by you putting your finger over the IAC bypass port then we know that that valve is not playing a factor in the idle. That just leaves a vacuum leak somewhere that you need to find.
Doug

 

[southrneclipser]

I think an excesive amount of air is getting past the throttle plate. Because when I cover up the throttle body intake the idle goes down, But when I cover up the IAC port it does not change. But I will look into it and will post my findings. Thanks.

 

[Doug99RS]

If the engine runs at all with the throttle body completely covered up then you've got a vacuum leak. The throttle body should be the ONLY source of air to keep the engine running. At the TB there should only be two means for air to get in, throttle plate gap (some is normal) or IAC passage.

If you're blocking off the TB completely and it still runs AT ALL then you have a vacuum leak.

 

[southrneclipser]

Ah ok, good i just was wondering if it could be a bad sensor or something even though they are all brand knew.

Well i sprayed carb cleaner around the injectors and it did not bring the idle down but i did notice that it was sucking in the carb cleaner around the injectors. So i'll replace the O-rings here soon and let you know how it goes. I don't see how it would be those though, because i never even touched the injectors when i changed the head gasket. And that's when it happened but since that's cheap and easy to do, i'll go ahead and replace them.

 

[Doug99RS]

If you sprayed all around the injectors and it did not change the tone of the idle then I don't think it's going to be your problem, personally, I would have replaced every o-ring, gasket and seal if I were doing the work on my own car but to each their own.

Did you remove the intake manifold from the head during the head repair?

 

[#40Fan]

I have a 95 rs with the 420a. Its mostly stock with only intake and exhuast. Stock fuel system. Deleted emissions and vacs.
It has new TPS and idle control valve.

I never had an idle problem until i changed the head gasket. I did not remove the intake manifold when i pulled the head off so i didn't replace the gaskets.

When i crank up the car it idles at 1200 rpm, but when it heats up it'll hang around 2000 rpm. I've sprayed carb cleaner all over the intake manifold and it didn't bring it down. I can't find any vacum leaks or anything like that. I can't figure out what it is. When i put my hand in front of the throttle body and cover it up, it will bring the idle down but the car still runs, so does this mean it's still sucking in air somewhere? Also when i pump the brake it will make the idle fluctuate up and down. So what could it be? Could i have a crack in the intake manifold or something that i haven't found?

There is a hose that runs from your intake manifold to the power brake booster. At the end of that hose is a plastic 90*. While holding the hose as close to the 90* as possible, wiggle it out of the brake booster. Cover the end of the plastic with your finger and have someone start the car. Or, if you are fast enough, do it while it is running. See if the idle slows.

 

[southrneclipser]

If you sprayed all around the injectors and it did not change the tone of the idle then I don't think it's going to be your problem, personally, I would have replaced every o-ring, gasket and seal if I were doing the work on my own car but to each their own.

Did you remove the intake manifold from the head during the head repair?

I know i should have but i didn't have the money at the time. But anyways no i haven't removed the intake mani from the head at any time since i'v had the car.

I changed the injector o-rings but it still idles high. I also did what #40FAN suggested but it still didn't help.

The only things left now to change are the upper and lower intake manifold gaskets and the intake mani itself. However i still feel like those are not my problems because i have soaked them in carb cleaner before. I really just don't know anymore.

 

[Doug99RS]

Double check to make sure that the EGR tube gasket is in place. Also, when they get removed they can leave residue of the gasket on the intake, the tube flange or both. You can reuse the gasket most of the time if you match the gasket back to the way it came off. If the gasket slips or falls out of place or is installed in a manor different from how it came off then you could suck in air.

Unfortunately, it's hard to diagnose things over the net sometimes. Before you remove the parts, try taking a BUNCH of pictures and posting them up for us to look over it. Before posting, view your pictures to make sure they are clear and show all the suspect areas. Maybe we can see something that you're not catching. It's just a thought and is easier than pulling parts first.
Doug

 

[southrneclipser]

i know its not my egr because i used a new gasket when i deleted the egr tube. Then i welded up the hole it the egr plate on the throttle body, then i covered it in form-a-gasket junk just to make sure no air was getting in.

But anyways i think my engine is about to poop on me so i'm going to get one from a junkyard and rebuild it at which time i will replace EVERY gasket, seal, etc.