Idle Hang Revisited

[kowalski vanishing point]

Hey, I'm back with the same problem.
'97 GTS that has "Idle Hang" the condition wherein the car spontaneously
makes up its mind to idle at 1500 RPM for a while
defying all attempts to bring the idle down
then after 5-20 minutes it spontaneously drops back down to a normal idle of
around 660 RPM.

This weekend I finally got around to hooking up my "EASE Diagnostics" software
to the car using a laptop and a connection to the OBD II port.
This is an excellent program and I've used it successfully to sleuth out problems on a few different cars.
What I found was, at least to me, very surprising.
Hopefully a knowledgable member here will have some answers.

1. When my Viper idles at normal (660) RPM it is constantly running lean.
The primary O2 sensors almost never go above .20 volts. They just stay flat.
No cycling whatsoever. No MIL lights go on. No DTC codes set.
I assume the computer sees this as a normal state of affairs.

2. Before "Idle Hang" occurs it is heralded by a few bumps of the O2 sensor voltage to about .40 volts (both sides). From experience I can tell by the way
the RPM blips a little that the car is about to go into "Idle Hang".

3. When the car goes into "Idle Hang" the O2 sensors are cycling normally
between about .10 volts and .90 volts. THe temperature usually drops by 5 to 10 degrees. As long as the O2 sensors cycle the car stays in "Idle Hang".

4. Long term fuel trim side 1 = around 7.
Long term fuel trim side 2 = around one.

5. At 660 Rpm idle the spark is advanced 2 degrees. Manifold pressure 12 mmhg.
At 1500 rpm idle the spark is advanced around 20 degrees and the
manifold pressure is around 25mmhg.

6. In around the town driving, RPM greater than 1500, the O2 sensors Cycle quite normally and the coolant temperature drops.

7. It is in "closed loop" mode the whole time this is happening.

Questions.

1. Is it normal for the Viper to idle in a lean state?
If not then why are no DTC codes set? No MIL lights lit?

2. Could a vacuum leak force the computer to run the engine lean
in order to meet a specified idle speed? If that is the case shouldn't the
computer recognize that the O2 sensors aren't cycling and set a DTC code?
I have searched high and low for a vacuum leak without success.
Replaced the intake manifold gaskets.
No leaks found, no success enjoyed.

3. If Vipers do run a lean idle, then what could be causing the the car to
come out of that mode and why again would no DTC codes be set?

4. Someone here once suggested having a Viper Tech reflash the PCM.
Does this sound like a PCM that simply does not know what it is doing anymore
and might benefit from getting reflashed?
I live over 100 miles from a Viper ready dealership and can't get off work easy.
Is there anyone I can mail my PCM to to have it reflashed?

5. Shouldn't a "closed loop" mode force the computer to vary the fuel injector
delivery so as to cycle the O2 sensor voltage?

Thanks for any help.
I can always hook up the computer again this weekend and get more info
if more info is needed.

 

[TOOOFST]

Had a 97,the dealer replaced the idle speed device.You should call the problem in and have them order the part in advance.Miss that 97cam.

 

[Bob D]

I had that problem last year and it was the throttle position sensor. It was causing the idle air control motor to freak out.

 

[RockyTop]

I have had this symptom for more than 3 years. It is intermittent and not a huge issue, but it is a pain and cannot be the way the car is designed to operate.

 

[RockyTop]

We reflashed the PCM to no avail. My tech and I think it's the IAC motor. My TPS may also be contributing. I hadn't thought of that.

 

[Toby]

my 96 GTS has done it a few times in the 300 miles I have owned the car. Doesn't bother me other than it brings my attention to it when it happens. Usually only lasts a few seconds then goes back to +-600 rpm. A burp of the throttle usually brings it down.

 

[kowalski vanishing point]

I've replaced the TPS and the IAC motor
to no avail.

Seems like if it was the IAC motor then that should have
set off a DTC code i.e. the computer should note that
the O2 sensors aren't cycling appropriately.

The TPS: what are the odds I replaced a bad one with another bad one?
The computer might not set off a DTC code if in its opinion
the lean condition was being caused (in its mind)
by the driver screwing around with the throttle
so that would make sense.
Still, why would it try to set idle speed
if it thought the driver did not want idle speed?

I'll have to hook up the computer again this weekend
as I remember the Throttle Position reading 16% at idle
but I din't remember if that was in range.

Thanks for all the answers so far.

 

[ViperGTS]

This happens to me too. With A/C ON. Switching A/C to OFF brings the idle back to normal!

 

[jcaspar1]

Had something similar happen with my 97. At startup would idle at 1500-2000. Could not bring it down. Took it to dealer and it had tripped nearly 20 codes. After some work they found out it was the battery. Replaced that and no problems since. Judging by my VEC 1, it is normal to be lean at idle.
Change the battery if it is the original.

 

[SneakyPete]

I've replaced the TPS and the IAC motor
to no avail.

Seems like if it was the IAC motor then that should have
set off a DTC code i.e. the computer should note that
the O2 sensors aren't cycling appropriately.

The TPS: what are the odds I replaced a bad one with another bad one?
The computer might not set off a DTC code if in its opinion
the lean condition was being caused (in its mind)
by the driver screwing around with the throttle
so that would make sense.
Still, why would it try to set idle speed
if it thought the driver did not want idle speed?

I'll have to hook up the computer again this weekend
as I remember the Throttle Position reading 16% at idle
but I din't remember if that was in range.

Thanks for all the answers so far.

I am having the same problem also. check TPC, IAM, TB settings. Sean Roe and I have gone through the car 3 times everything was working except the pcm. The only way we found the problem was swapping out the PCM. We put the PCM from Sean's car into mine and the idle hanging problem went away. When Sean put my PCM into his car it imediately set a code-Idle air sensor internal error. Why it sets a code in his car and not mine is beyond me.

If you have a friend with simalar year car, switch pcm's and try it out. It fixed my problem. Only problem is dealer order new pcm under warantee, but part is on back order.

 

[ViperGTS]

I switched the PCM - no change...

 

[genXgts]

Mine has a severe hanging idle under heavy throttle "sessions".

I can drive for an hour light footed and swings down to sub 1000 as it should.

Run thru the gears at WOT and it sticks all over the map, a blip brings it back down to normal. After a "cooling off" period things return to normal.

Wonder if it's related to any of the above conditions??

 

[Gerald]

I notice I have SEVERE hanging problems also

IF

1. I'm under heavy acceleration, then let off pedal, sometimes will stick at 1k - 1,500 RPM
2. Dusty road makes it stick everytime also, or a dusty parky lot / stall
3. A quick "bling" of the pedal usuall drops it, but this gets old after 2-3 blings a minute while driving

The hanging idle will get better or worse if I mess with the throttle body synch.
The only positive thing about a hanging idle is I have automatic cruise control

I've changed IAC motors a couple times, I've replaced my Throttle Positions Sensor a couple times, adjusted throttle bodies a hundred times.. etc, NOTHING helps. I wish someone would find a definate solution to this ANNOYING problem...

Dodge are you listening?

 

[GTS-R 001]

I have one of Sean Roe's new pcm's coming to me tomorrow, I'll let you know if it fixes my hanging idle ( same as gerald's, very annoying )

 

[kowalski vanishing point]

Seems like finding the answer to this
would be the "Holy Grail" of '97 Viperdom.

Everyones "Idle Hang" is similar and yet different.

Let's see what happens with EdmuntonGTS' new PCM.
Beware though that for the first 300 miles or so
after the battery has been disconnected
the computer will be in an acquiring mode
and may run fine for a while (I know, I've been fooled by this, thinking I'd come across a cure after some repairs only to have the car act up again after 300 or so miles).

And the problem can be more than an annoyance
my Viper at first didn't pass smog because its idle was out of range
and luckily the car decided right before the guy failed me
to drop back down to 660 RPM and get itself passed.

 

[SneakyPete]

I have one of Sean Roe's new pcm's coming to me tomorrow, I'll let you know if it fixes my hanging idle ( same as gerald's, very annoying )

I have the same symtoms as Gerald also, I am not going to wait for DC to get a PCM, I am going over to Sean Roe's tomorrow to put on in.

 

[ViperGTS]

bump - something new - still

 

[LETHAL GTS]

I'm now having this problem. It just started after a hard weekend at Mid America.

Edmonton GTS,
How's the new PCM from Sean??
Does it solve the problem??

 

[kowalski vanishing point]

I haven't had time to rehook my diagnostics program to the car, reading the one other thread though yielded a value of 20 mmhg for the idle vacuum which I recall mine idling at 12 mmhg. Vacuum leak? Still one would figure that if this was the case a DTC code should be set. Also someone mentioned the a lean idle (O2 sensor voltage ALWAYS 0.20 volts or less) was normal for a Viper. I don't see this in other cars I have tested (GM products). At Idle they cycle the O2 sensor between rich and lean as one would expect. Still waiting to see if the guys who were going to change their computers or have them reflashed got any results. There HAS GOT TO BE AN ANSWER to this widespread plague.

 

[Mike Adams]

Does every one here have stock throttle bodies ?

 

[ViperGTS]

>>>Does every one here have stock throttle bodies ? <<<

YES - my car has stock throttle bodies.

 

[MES]

From what I've experienced idle hang comes from too much air entering into the motor. I've found that the adjusting screw on the TB linkage has a big effect on the idle hang. Just one or two turns and I have major idle hang. Right now it's flush (screw all the way out) and I have no idle hang but just one turn and I get a lot. On each TB there is a stop nut which can be adjusted to allow the TB to close more. Also I recall (never tired it) that you can insert a smaller diameter hose into the idle motor hose to restrict the amount of air on idle down. Just some ideas as it's very annoying.

 

[Daniel Cragin/DC Performance Inc]

I have tackled this problem many times and have been able to fix most all of them. Depending on the tune of the engine the fix varys. Call me and I can steer you in the right direction.

Dan Cragin
DC Performance
310 841 6996

 

[HP]

I've replaced the TPS and the IAC motor
to no avail.

Seems like if it was the IAC motor then that should have
set off a DTC code i.e. the computer should note that
the O2 sensors aren't cycling appropriately.(quote)

The PCM will not throw a code for an open driver circuit to the idle motor
(There is 2 circuits in the motor - 2 contacts(aka drivers) for each circuit.
To test the circuits to the motor - Unplug the idle motor and test each of the 4 pins in the connecter with an ohmmeter connected to a ground - if any of the 4 connectors give a reading of less than 5.0 Ohms- then the wires are shorted to ground* each pin can be tested
against the 3 other pins in the same way to see if they are shorting out between the circuits. The check for a short in between the Idle motor and
the PCM - disconnect the plug from each and check measure the resistance in
each wire if it is less than 5.0 ohm - that wire is shorted to ground.** all
ohm test are done with ignition off.
At idle - each circuit(2 outer wires, or 2 inner wires - will indicate a voltage(intemittent or constant)
if the circuits are good. But since the concern is high idle - it would seem
that the idle motor is supplying more air past the throttle plates than needed-
which would indicate 2 of the circuits that supply power had shorted together or
the PCM is powering the circuits more than needed.
I have a 96 Gen-I motor - at idle my w/b A/F meter is a consistant 14.7
My car hasn't ever had a high idle problem - but I felt sorry for you guys,
so I had to add something. I don't really know what is the cause of all of
your problems - but in some respect it sounds like sticking throttle blades -
caused by grit or uneven thermal expansion between blades and throttle body, or
some other interference. But what do I know - I have a GEN-I and I have never
had high idle - sometime low idle, but never high idle.

 

[kowalski vanishing point]

Thanks for the info.
Will check it out this weekend.

 

[Jerry Dobson]

Dan,

Any idea why it comes and goes? If there was a problem, why would it not stay?

What are most of the fixes?
=Battery
=IAC
=TPS
=PCM


Jerry Dobson

 

[kowalski vanishing point]

I did notice something recently.

A few years ago when I changed the intake manifold gaskets I noticed motor oil in the intake runners. Not much but it was there. No real explanation for it. Recently I noted that the car was not "Idle Hanging" as much. I checked the oil and it was towards low but not quit to the low mark. Got the oil changed and the oil got back up to the high fill mark and now the problem is back. Is the oil getting out of the crankcase and into the intake manifold causing this? I've changed the PCV valve twice.

Maybe next time I'll ask them to put 7 1/2 quarts in and not 8 1/2 to see what happens.

 

[Vip-RT10]

I have stock TB's as well. I down shift all the time, that is my driving style. Driving the car I also noticed that if you are down shifting to stop at a light, keep it in second until it is about to "buck" and then press the clutch in, the idle hang is non existent and idles at the desired 600 range. I have reproduced this many times and it works for me so far, but it still puzzels me as well.

 

[JimDavis MT 97GTS 650R]

My hanging throttle problem seems to rear it's ugly head during very hot weather and hard running. I run larger aftermarket TB's. etc.

 

[Jerry Dobson]

I can down shift and "motor break" but in parking lots that does not work. At times I feel like an idiot driving through a parking lot with the motor reving.

I wish there was a PCM flash that would cure this common problem.

Jerry