Trooper Idle Problem

Lenny · October 8, 2009

If you remember, some of the Trooper owners out there have had a problem with the engine not wanting to idle down. Some time back I posted about cleaning the Idle air control valve which is mounted to the throttle body. I cleaned mine and it worked good afterwords. However it started to act up again, wouldn't idle. It's not getting any dirt into it anymore so I figured I would pull it off and check it. Found that dirt had gotten into the interior from before where where it can't get cleaned out and it was making the valve stick. The inside of the air control valve has a little motor that turns an armature with a threaded hole through it. The pin that sticks out has a threaded shaft on its hidden end which screws into the armature to move the pin in or out thus giving the engine more or less air for idling. Well, I got sick of fooling with it so I tried eliminating it by putting a plate over the spot where it bolts on to the throttle body, effectively blocking the port holes. I felt that if cars for years could sucessfully use an idle screw on the throttle butterfly shaft, I could do the same if the computer didn't care. It works. Just plate it over and pull the plug off the idle air valve and pitch it. No more idle problems nor the thought of having to buy a new throttle body just to replace the valve.

Lenny

ERV JR · October 8, 2009

If you remember, some of the Trooper owners out there have had a problem with the engine not wanting to idle down. Some time back I posted about cleaning the Idle air control valve which is mounted to the throttle body. I cleaned mine and it worked good afterwords. However it started to act up again, wouldn't idle. It's not getting any dirt into it anymore so I figured I would pull it off and check it. Found that dirt had gotten into the interior from before where where it can't get cleaned out and it was making the valve stick. The inside of the air control valve has a little motor that turns an armature with a threaded hole through it. The pin that sticks out has a threaded shaft on its hidden end which screws into the armature to move the pin in or out thus giving the engine more or less air for idling. Well, I got sick of fooling with it so I tried eliminating it by putting a plate over the spot where it bolts on to the throttle body, effectively blocking the port holes. I felt that if cars for years could sucessfully use an idle screw on the throttle butterfly shaft, I could do the same if the computer didn't care. It works. Just plate it over and pull the plug off the idle air valve and pitch it. No more idle problems nor the thought of having to buy a new throttle body just to replace the valve.
Lenny

Cars have also sucessfully used IAC's for years. All these things on these troopers have been used in cars for years and most have gone 200k. I think its part of the issue with QC and parts slection when these things were built. Have you even thought that all the sensors were on the engine for a reason ?

Lenny · October 8, 2009

Cars have also sucessfully used IAC's for years. All these things on these troopers have been used in cars for years and most have gone 200k. I think its part of the issue with QC and parts slection when these things were built. Have you even thought that all the sensors were on the engine for a reason ?

The IAC is Semens and should be a good quality. But, once dirt gets into it it creates a problem. I beleive the only function of the IAC is so the computer which moniters RPMs can maintain constant Idle RPM.

Lenny

Lenny · October 8, 2009

OOPS, I gave you a bit of misinformation. I said you could put a plate over where the IAC is removed. On mine, that's all I have to do because I'm using a different throttle body. On the stock throttle body, you have to put something into the hole where the pin reaches into to block the port. This could be something as simple as a marble with a wadded up peice of cloth behind it to hold it tight against the port hole. When the plate is put on over this, be sure it has to force the cloth tight against the marble. I know, pretty redneck but it's such an easy solution.

Lenny

Anylizer · October 8, 2009

If you remember, some of the Trooper owners out there have had a problem with the engine not wanting to idle down. Some time back I posted about cleaning the Idle air control valve which is mounted to the throttle body. I cleaned mine and it worked good afterwords. However it started to act up again, wouldn't idle. It's not getting any dirt into it anymore so I figured I would pull it off and check it. Found that dirt had gotten into the interior from before where where it can't get cleaned out and it was making the valve stick. The inside of the air control valve has a little motor that turns an armature with a threaded hole through it. The pin that sticks out has a threaded shaft on its hidden end which screws into the armature to move the pin in or out thus giving the engine more or less air for idling. Well, I got sick of fooling with it so I tried eliminating it by putting a plate over the spot where it bolts on to the throttle body, effectively blocking the port holes. I felt that if cars for years could sucessfully use an idle screw on the throttle butterfly shaft, I could do the same if the computer didn't care. It works. Just plate it over and pull the plug off the idle air valve and pitch it. No more idle problems nor the thought of having to buy a new throttle body just to replace the valve.
Lenny

As Erv stated there are reasons for these and other sensors. One major input is the TPS (throttle position sensor).

This tells the ECU what the throttle opening is, so proper fuel amounts, among other things can be provided. Eliminating the IAC could cause problems down the road. A proper setting of TPS voltage needs to be done by a qualified tech w/ the proper equiptment.

Also, the newest IAC units have been changed from "siemens" to "continental". I'm not sure if these are better or not. What I can tell you is that after replaceing the IAC on a given unit, the problem has not re-occured.

Lenny · October 8, 2009

As Erv stated there are reasons for these and other sensors. One major input is the TPS (throttle position sensor).
This tells the ECU what the throttle opening is, so proper fuel amounts, among other things can be provided. Eliminating the IAC could cause problems down the road. A proper setting of TPS voltage needs to be done by a qualified tech w/ the proper equiptment.

Also, the newest IAC units have been changed from "siemens" to "continental". I'm not sure if these are better or not. What I can tell you is that after replaceing the IAC on a given unit, the problem has not re-occured.

I didn't say to eliminate the throttle position sensor. There are two seperate devices on the Throttle body, one is a sensor and the other is an actuator. One provides information to the computer and the other receives information from the computer in the form of a positive or negative current. It's not the quality of the IAC in my case, it's the dirt. The pin should move in and out smoothly. You can actually do this by pushing and pulling on it. Mine would be smooth for part of the stroke and then hit a rough spot then get smooth again. I tried to work and wash it out but could never get it all out and finally got sick of it. It would work for a while then the dirt would find it's way back into the threads again. The computer uses the input from the throttle position sensor to change spark timing and the fuel mixture as engine load changes. For example if the throttle is opened rapidly, the computer will leave the injectors on a little longer sort of like the accelerator pump of carburetor systems. On the other hand, the IAC doesn't send any information back to the computer. It's the end of the line for a specific function. If the computer detects the idle RPMs is droping below a minimun value, it opens the IAC more until the RPM is correct. I see no reason that eliminating it will cause any problems. If you were to eliminate the TPS then there would be problems. IMHO If i'm missing something, let me know the specifics. When you say it's going to cause problems, just what is the problem and how does the IAC cause it. After all, I use this forum to learn where I'm wrong and to learn new stuff. Everybodys input is always valuable.

Lenny

Anylizer · October 8, 2009

No Lenny, you got me all wrong.

All I was trying to say was that there are reasons or purposes for all of the existing components.

Just yesterday, an idle issue was resolved using proper calibration of the TPS. Changing or cleaning the IAC had no effect.

Also the pushing & pulling of the IAC..... WILL CAUSE DAMAGE!!!! The threaded shaft is only plastic, and can be damaged very very easily. Yes this is experience talking.

You are correct that the IAC has no input, but controlling idle by throttle plate opening/position, changes the TPS input. This is not the correct way to control idle on Multi-port Fuel injection systems. Not saying it doesn't work, but may cause other drivability issues becuase of wrong TPS inputs. =) A.

Lenny · October 9, 2009

I agree, it wouldn't be hard to damage one. The throttle butterfly is just bearly cracked open when at idle. In fact I didn't even have to set the idle screw as it idled about right, right from the get. The difference in the throttle position at idle is probably not but 1 or 2 degrees from fully closed. Beyond that, it is at the same position it would be anyway and the IAC wouldn't be doing anything off idle. I can see how a mis-calibrated TPS could effect idle. If the computer thinks the engine is running to fast because of this calibration error, when it really isn't running to fast, it will cut the air flow possibly shutting the engine down. Or, vise versa. I'm not a car guy nor do I have lots of expierence with this stuff. However, I'm pretty sure that if the computer was looking for data from the IAC that it wouldn't run at all without it. I'm not detecting any difference in its drivability with the IAC out of the circuit. That said, your probably right as i'm out of my area of expertise with engines. I am stubborn so I can't change easily. If you tell me I can't do something, well, I figure that is exactly what I should do. Isn't that called going against the wind. I've made a lot of money in my lifetime designing products to preform in a particular way when the industry was telling me that it couldn't be done. To bad I didn't manage to hang onto more of it then I did.

Lenny

ERV JR · October 10, 2009

I guess I look at this stuff dufferently coming from a automotive backround. I have worked at dealer and have been to alot of school where I take advantage of what they are teaching and listen and read alot more than what others do. I also have been involved in alot of fab work and drag racing. I have done stuff for Sema project cars and trucks. So I understand what you are saying about building your own parts and doing it your own way. But as I said I have seen cars with over 200K on them so alot of these ideas are not new and work.

There is alot that can be applied to these things and am sure there are more ways than one to get the end result. I give things a different look due to the fact that I drag race, build drag motors and chassis setups. I have friends that have desert car shops that do race prep and pre run and pit for race teams. I toss my ideas off them and they do the same . Its the same as all of us here

Lenny · October 12, 2009

Thanks EVR JR and Anylizer for the input. Like my wife says, "it's a good thing that someone keeps you corraled or you would be falling off the deep end all the time". I don't like being corraled, but being hipper, I do get ahead of myself every now and then. Well, this weekend, I went to Dumont Sand Dunes in California. Wanted to try the new power with my big paddle tires I run. (16.5-15 rear and 13.5-15 front) Scoots up the dunes real good. Well the sandrails, raptors and banchies blew me away but when it came to continuing to climb, although slower, I could go up any of it except the really big stuff. Here I still ran out of power. I did have a problem though and my first thought was, "Dam, I don't want to admit that you guys might be right". I'll never really do that but I'll conceed, there is a minutely small chance you could be. Dam again. As long as I was into the throttle it ran fine but when I let up to just cruse, it would cut out and then kick in again and out again and, well you get the idea. Once it settled down to an idle, it was fine again. I noticed that the fuel regulator would drop to 0 psi and immediately go back up to it's normal value when it cut out. It's so consistant that it doesn't act like a short. I suspose it could be the fuel pump or possibly fuse. That's my next project, to find what is wrong. God forbid, I sure don't want you guys to be right about the IAC. I thought my defense was halfway reasonable.

Lenny

Lenny · October 13, 2009

Found this on the internet and thought I would share it. Pretty much comfirms what we have been suspection all along about contamination in the IAC.

Failure of an idle air control valve in a gasoline-fuelled automobile

References and further reading may be available for this article. To view references and further reading you must purchase this article.

D. S. Rao and S. Srikanth,

National Metallurgical Laboratory Madras Centre, CSIR Madras Complex, Taramani, Chennai-600 113, India

Received 8 August 2003; accepted 12 August 2003. Available online 23 October 2003.

Abstract

The functional failure of an idle air control valve in a gasoline-fuelled automobile in India has been analyzed. It was found that the failure was related to the formation of deposits inside the idle air control valves. The deposit was found to contain both organic and inorganic constituents. The deposits were characterized using a variety of techniques including chemical analysis, optical microscopy, FTIR spectroscopy, GC–MS, X-ray diffraction and thermal analysis. The possible source of the deposit formation has been analyzed. It is inferred that the cause of deposit formation and the subsequent failure of the idle air control valve is because of the back flow and condensation of fuel vapor combined with contamination through extraneous dirt especially silica from the air intake system.

Author Keywords: Automotive failures; Valve failures; Deposit formation; Spectroscopic analysis; Microstructures; X-ray analysis

Lenny

Lenny · October 13, 2009

Found this on the internet and thought I would share it. Pretty much comfirms what we have been suspection all along about contamination in the IAC.
Failure of an idle air control valve in a gasoline-fuelled automobile

References and further reading may be available for this article. To view references and further reading you must purchase this article.

D. S. Rao and S. Srikanth,

National Metallurgical Laboratory Madras Centre, CSIR Madras Complex, Taramani, Chennai-600 113, India

Received 8 August 2003; accepted 12 August 2003. Available online 23 October 2003.

Abstract

The functional failure of an idle air control valve in a gasoline-fuelled automobile in India has been analyzed. It was found that the failure was related to the formation of deposits inside the idle air control valves. The deposit was found to contain both organic and inorganic constituents. The deposits were characterized using a variety of techniques including chemical analysis, optical microscopy, FTIR spectroscopy, GC–MS, X-ray diffraction and thermal analysis. The possible source of the deposit formation has been analyzed. It is inferred that the cause of deposit formation and the subsequent failure of the idle air control valve is because of the back flow and condensation of fuel vapor combined with contamination through extraneous dirt especially silica from the air intake system.

Author Keywords: Automotive failures; Valve failures; Deposit formation; Spectroscopic analysis; Microstructures; X-ray analysis

Lenny

I'm adding to the previous post. I did not post the entire article which gets into car make variances.

The following is published by:

WELLS Manufacturing Corp.,

P.O. Box 70, Fond du Lac, WI 54936-0070

T H E E L E C T R O N I C, D I A G N O S T I C A N D D R I V E A B I L I T Y R E S O U R C E.

Volume 4 Issue 1, January 2000

continued on page 3

IDLE-AIR CONTROL-VALVE DIAGNOSIS

A common condition is an idle-air bypass valve

that’s fully extended (closed). This is often a

symptom of an air leak downstream of the

throttle, such as a leaky throttle-body base gasket,

intake manifold gasket, vacuum circuits, injector

O-rings, etc. The computer has closed the bypass

circuit in an attempt to compensate for the

unmetered air leak that is affecting idle speed.

Incorrect idle speed (too high) also can be caused

by a shorted A/C compressor clutch wire or

defective power steering pressure-sensor circuit.

A code 35 on a GM application indicates a

problem in the idle-air control circuit. To

troubleshoot the problem, disconnect the IAC

motor, then start the engine to see if the idle speed

increases considerably. Turn the engine off,

reconnect IAC and start the engine again. This

time the idle speed should return to approximately

the previous RPM. If it does, the problem is not

the IAC circuit or motor. Check for vacuum leaks

or other problems that would affect idle speed.

If the idle speed does not change when the IAC is

unplugged, and/or does not decrease after

reconnecting the unit, use a test light to check the

IAC wiring circuits while the key is on. The test

light should glow when connected between

terminals A and B and terminals C and D if the

PCM and wiring are okay (indicating the

problem is in the IAC motor). If the test light

fails to glow on either circuit, the fault is in the

wiring or PCM.

When installing a new GM IAC or Chrysler AIS

motor, the pintle must not extend more than a certain

distance from the motor housing. The specs vary, so

check the manual. Chrysler says one inch (24.50 mm)

is the limit, while some GM allow up to 28 mm on

some units and 32 mm on others. If the pintle is

overextended, it can be retracted by either pushing it

in (GM) or by connecting it to its wiring harness and

using actuator test #03 to move it in (Chrysler).

Digital Storage Oscilloscope (DSOs) can also be used

to view IAC wave forms. A typical GM is illustrated

above (Figure C).

Hope this information is useful.

Lenny

jamesrulz · October 16, 2009

I agree with the guys mentioning that the IAC can cause idle issues after all it is the idle air controle valve. I just wanted to share an issue i had with my trooper. I chased a hard start issue for a while and after messing around with many checks it turned out to be the computer. The computer isnt sealed what so ever so it is easy to get water into even just with a wash gun. Something to think about if you dont have any luck with your throttle body and IAC could be the brain not telling it what to do properly. GOOD LUCK