Why does the idle dip when I come to a stop?

The 2nd Gen Board is for general questions regarding the second generation of Neons (2000 - current.) Rumors, hints, tips-and- tricks, and all general maintenance and repair questions belong in this forum, as well as beginning modification queries.
Post Reply
HottRodd
Neon Enthusiast
Posts: 995
Joined: Thu Feb 25, 2016 7:11 pm
Location: Brossard, Quebec, Canada

Why does the idle dip when I come to a stop?

Post by HottRodd » Sat Jun 09, 2018 5:16 pm

Strange how it dips at a light or stop then I put it into neutral and it goes back up. It's not rough in fact it's really smooth. Seems to have appeared after I changed the size of my wheels , from 175 to 205 . Is this transmission related or sensor, or pcm . I've been told my computer for the trany is in the pcm. So can I test it ? The hole in the throttle body doesn't seem like a fix to me. Everything seems to work ,IAC , TPS , all other sensors too . Maybe my high flow Cat ihas something to do with it? Modern electronics can be so (what the). It goes down to 600 rpm instead of the 730 it's supposed too.
Does anyone have a real experienced explanation for this? Should I take it too trany guy? ....... help....
The 2003 2.0sx guy, 30k original miles :dance:
30k is that possible, Yeah :good: :

occasional demons
Master Neon Mechanic
Posts: 11367
Joined: Fri Apr 13, 2007 10:34 am
Location: Ashland, Ohio

Re: Why does the idle dip when I come to a stop?

Post by occasional demons » Mon Jun 11, 2018 5:48 am

HottRodd wrote: Sat Jun 09, 2018 5:16 pm Strange how it dips at a light or stop then I put it into neutral and it goes back up.
Normal.

The PCM isn't really going to take any action unless it falls below ~400 rpm. Example: My '01 will shut off the A/C at idle, because the compressor load is more than the power at idle can manage. This is due to engine condition, and nothing else. If it was an ATX car, it would probably stall in gear at a light.
HottRodd wrote: Sat Jun 09, 2018 5:16 pm It's not rough in fact it's really smooth.
For this you should be happy. If it's not "broke" don't fix it.
- Bill

desmodromic wrote:You have to remember what's important here, while they make New humans everyday, they'll never make another Neon.
Skellibert wrote: Fri Oct 13, 2017 3:42 amThis is a daily by the way, not a track car or fun buggy.

HottRodd
Neon Enthusiast
Posts: 995
Joined: Thu Feb 25, 2016 7:11 pm
Location: Brossard, Quebec, Canada

Re: Why does the idle dip when I come to a stop?

Post by HottRodd » Mon Jun 11, 2018 8:46 pm

It's sort of funny ,it's like the IAC doesn't trigger at the lower rpm unless you turn on the ac or slip it into neutral (or 400 rpm you said ) which is the case after it warms up and I put it into drive , it dips to stall the it comes back to life when the IAC opens up. I tested the IAC and it opens when voltage is applied. . Question is , is it not getting voltage when it is supposed too, or is there something else afoot? The whole it want to stall when I engaged it when it's warm is to hard to ignore. Think I will recheck the compression and have a look inside the combustion chamber with my borescope. Would a head gasket leak cause this mmm.
The 2003 2.0sx guy, 30k original miles :dance:
30k is that possible, Yeah :good: :

Aidenbrae84
Neon Enthusiast
Posts: 99
Joined: Mon Aug 21, 2017 8:54 pm

Re: Why does the idle dip when I come to a stop?

Post by Aidenbrae84 » Thu Jun 14, 2018 11:50 pm

I think you're chasing a ghost. This is neon-101 "nature of the beast". I've had 4 neons, all 2nd gen. 01, 03, two 05s, and one 00 as a parts car. All of them, while they ran beautifully, no CEL or codes at all, they ALL did it. The only difference I noticed is that the 01 has a power steering pressure sensor that will lift the idle if you just turn the wheel slightly one way or the other. Also, the 01 only does it with the A\C off, after its up to operating temp. The other 3 did it from day one, and always required either slipping into neutral and back to D, or just a quick blip on the gas pedal, after that they would idle fine until the next stop sign.

HottRodd
Neon Enthusiast
Posts: 995
Joined: Thu Feb 25, 2016 7:11 pm
Location: Brossard, Quebec, Canada

Re: Why does the idle dip when I come to a stop?

Post by HottRodd » Fri Jun 15, 2018 9:03 pm

Man , I don't mean to be ......you know but what....... this just started happening . It was fine before. Have you ever heard the expression there is a reason for everything. . Dude ignoring it is dumb . Just because you can't figure out why something happens doesn't make it "normal ". My Car has 48 000 km on it not 200 000 . .
I don't want to sound ungrateful but , fuc man that's not normal. ...... understand. I don't give a peanut about you experience. I don't need anymore to tell me what's normal when it comes to driving a car , trust me I can tell. . There is always a reason. ...... it just how to find it , not ignore it......
The 2003 2.0sx guy, 30k original miles :dance:
30k is that possible, Yeah :good: :

HottRodd
Neon Enthusiast
Posts: 995
Joined: Thu Feb 25, 2016 7:11 pm
Location: Brossard, Quebec, Canada

Re: Why does the idle dip when I come to a stop?

Post by HottRodd » Fri Jun 15, 2018 9:26 pm

Just to add ....... it almost stalling when I put it it drive when it's warm is also not " NORMAL " Especially when my compression is over 180 for each cylinder.
The 2003 2.0sx guy, 30k original miles :dance:
30k is that possible, Yeah :good: :

Aidenbrae84
Neon Enthusiast
Posts: 99
Joined: Mon Aug 21, 2017 8:54 pm

Re: Why does the idle dip when I come to a stop?

Post by Aidenbrae84 » Sat Jun 16, 2018 5:59 pm

Well I believe the hundreds of other posts regarding you're exact problem is just as helpful as your attitude.
You figure it out...

Sent from my Moto G (5S) Plus using Tapatalk


Aidenbrae84
Neon Enthusiast
Posts: 99
Joined: Mon Aug 21, 2017 8:54 pm

Re: Why does the idle dip when I come to a stop?

Post by Aidenbrae84 » Sat Jun 16, 2018 6:16 pm

Also, our experiences may be very different. The idle "dip" is very common, you'll find plenty of info. But mine doesn't come anywhere near stalling or anything, just randomly drops to a lower idle while at a stop. It's not an every time thing and it's not violent or horrendous. I hate it and I wish I could figure it out, but I've tried many different things.
Yours may be a different issue perhaps related to vacuum or intake, there are plenty of options. I wish you luck and hope you can figure it out, bc I agree. There's always a reason for a problem, and I, too, can tell immediately when something is wrong. But in my experience (which you made clear you didn't care about, although that's what a forum is), it has been a very normal behavior. So good luck, I hope you figure it out. But all I was doing is sharing my experience. It's why I'm a member of this forum.

Needless to say, I won't have any more contribution to this thread.

Sent from my Moto G (5S) Plus using Tapatalk



HottRodd
Neon Enthusiast
Posts: 995
Joined: Thu Feb 25, 2016 7:11 pm
Location: Brossard, Quebec, Canada

Re: Why does the idle dip when I come to a stop?

Post by HottRodd » Sun Jun 17, 2018 2:48 pm

I didn't mean to be mean ...... it's just I'm getting to the end of my patience with this car. If I could sell it for a reasonable price I would buy a 200 with the v6 , no more power problems . This car has been somewhat of a nightmare. It has such low mileage it isn't conceivable that it should have any problems. I'm sorry if a stupid inanimate object has caused me to offend you . Maybe I should cut my losses and see about that 200 c . God I hate the payments, but it's surly better than the headaches of a car that seems to develop a problem as soon as you fix one.
The 2003 2.0sx guy, 30k original miles :dance:
30k is that possible, Yeah :good: :

User avatar
NickKo
Global Moderator
Posts: 10156
Joined: Wed Apr 17, 2002 10:53 pm
Location: -1 1/2hr. East of Belvidere,IL.-

Re: Why does the idle dip when I come to a stop?

Post by NickKo » Tue Jun 26, 2018 8:28 am

Here is something that I have found out which helps with the 'low-idle' condition that 2nd Gen Neons are known for:
Be sure that the IAC pintle and passage are *Absolutely* clean.
As in, clean enough to lick with your tongue (not that I recommend actually doing that.) :grin:

There does not have to be much, if any, carbon / grime buildup on the Idle Air Control pintle, and passage, for it to affect idle quality.
You know the black 'grime' and soot buildup that takes place inside the throttle body ?? Be sure to get rid of ALL the 'black grime'.
There should be no 'black grime' or soot - Only clean plastic.

You probably already know not to use any 'harsh' chemicals (like brake cleaner, or even worse, carb cleaner) on the inside of the plastic throttle body.
I would clean both the I.D. bore of the throttle body, as well as the IAC passage / port and the 'pintle' tip, of all the 'black grime'.
You should notice an improvement in the idle quality after cleaning it out.


- Nick
-1998 2-dr SOHC MTX= 52mm TB; Maddog STS
-1999 4-dr DOHC ATX= went to car heaven (junkyard)
-2000 Ply.LX with MTX = Maddog STS; CAI; R/T muffler + Header
-2001 Ddg.ES ATX = UDP, Magnum Header; + Syked PCM 'pending'

-1971 Ply.Scamp SL6cyl. ('Horse Traded' away)
-1968 Chry.300 w/440 V8 (sold)
"MoPar or No Car"

HottRodd
Neon Enthusiast
Posts: 995
Joined: Thu Feb 25, 2016 7:11 pm
Location: Brossard, Quebec, Canada

Re: Why does the idle dip when I come to a stop?

Post by HottRodd » Tue Jun 26, 2018 6:09 pm

I did clean it recently. Air cleaner is spotless. I plan to disconnect everthing this weekend check and clean . Strange how I get a down at the light . It's like something isn't working, like in neutral there is something telling it it's in neutral to open the pintle but stopped at a light it doesn't but did before treat like it was in neutral or park . With the ac on it doesn't do it other than the so called parasitic drain, so it has to be the IAC just not getting a signal from the trany computer which is in the pcm.

Is there a switch or sensor in the trany (atx) which relates the rpm of the torque converter to the pcm ? Sort of like a neutral switch. ...
Funny this happened before but when away . Then I had to disconnect the battery, and after reconnection it came back and has yet to go away..

How about , this might sound weird but ..... the pvc opens at the stop light and because my car maybe is producing an abnormal amount of gases ,and nothing to tell the IAC to open up , the gases cause the idle to drop . Only one way to test this , block the pvc line , just long enough to check it out..
I have set aside 2 days this holiday weekend see if I can get this done . I have one abnormally loud lifter I will change. Maybe it's tap tapping is making too much gases. . I have a new inspection camera . Will check each piston from inside also . See come Sunday if I got this figured out.


P.S Does anyone know what the proper psi the ac should be at (high pressure and low pressure ) I will be doing an ac check also on the weekend with a good guage.
The 2003 2.0sx guy, 30k original miles :dance:
30k is that possible, Yeah :good: :

occasional demons
Master Neon Mechanic
Posts: 11367
Joined: Fri Apr 13, 2007 10:34 am
Location: Ashland, Ohio

Re: Why does the idle dip when I come to a stop?

Post by occasional demons » Wed Jun 27, 2018 10:01 am

The PCV valve is not regulated by anything other than manifold vacuum, and the condition of the tubing and valve.

The range sensor on the ATX would send a signal telling the PCM it is in gear or neutral. It may open the IAC slightly to compensate for being in gear, but given the low idle issues with ATX neons, I don't think this accounts for much.

The VSS sensor tells it when it is in motion, and the idle is raised accordingly. It drops when the vehicle comes to a stop.
- Bill

desmodromic wrote:You have to remember what's important here, while they make New humans everyday, they'll never make another Neon.
Skellibert wrote: Fri Oct 13, 2017 3:42 amThis is a daily by the way, not a track car or fun buggy.

G3nmaL0rd
New
Posts: 1
Joined: Tue Jul 24, 2018 6:15 pm

Re: Why does the idle dip when I come to a stop?

Post by G3nmaL0rd » Tue Jul 24, 2018 6:17 pm

The reason for the RPm dip at idle is Chrysler programmed the car to do that for better fuel mileage at idle

occasional demons
Master Neon Mechanic
Posts: 11367
Joined: Fri Apr 13, 2007 10:34 am
Location: Ashland, Ohio

Re: Why does the idle dip when I come to a stop?

Post by occasional demons » Wed Jul 25, 2018 1:18 pm

Severe idle undershoot wasn't a planned design flaw.

It was mostly an issue in the early to mid nineties cars, but it can also be an issue in newer cars, more so in ATX cars.

My '94 41te V6 Shadow would occasionally stall out from idle undershoot when coming to a hard stop. It could be partially from the TC not "releasing" fast enough when stopping quickly, or just the IAC not reacting fast enough, and have nothing to do with the PCM's programming.

Near stalling from going from park or neutral to drive or reverse is something different. Not 100% sure if DCX utilized the range sensor to tell the PCM it is in gear or not. Other makes will raise the idle noticeably when the gear selector moves from park or neutral. It can be annoying, especially on slick surfaces.
- Bill

desmodromic wrote:You have to remember what's important here, while they make New humans everyday, they'll never make another Neon.
Skellibert wrote: Fri Oct 13, 2017 3:42 amThis is a daily by the way, not a track car or fun buggy.

HottRodd
Neon Enthusiast
Posts: 995
Joined: Thu Feb 25, 2016 7:11 pm
Location: Brossard, Quebec, Canada

Re: Why does the idle dip when I come to a stop?

Post by HottRodd » Wed Jul 25, 2018 7:34 pm

I'm starting to think my IAC just doesn't open enough, or after changing both O2 sensors the learning of my pcm on long term fuel trim may be causing the pcm to not being able to notice the simularity between being at a stop and being in neutral. . The fact I use 91 octane not 87 on a base setup with a modified exhast oversized wheels (205) might have changed the base enough to say that it is to far from stock for the computer which is not evolved enough to make the necessary changes to retain stock rpm . I haven't touch it in a while . (It rains too much on the weekends ) Kinda lazy too . One heatwave after another does that to me. Check engine came on tonight on the way home . Figure it out tomorrow. Going at it alone can be so boring. Rebuilt my rear brakes . New springs are sure a pain to get on. My old adjusters were seized. Baby is getting old . Just like me . Still wish I had a garage. ....sure would make it easier. Would love to take the head off . Hope it doesn't rain this weekend. ... later...
The 2003 2.0sx guy, 30k original miles :dance:
30k is that possible, Yeah :good: :

occasional demons
Master Neon Mechanic
Posts: 11367
Joined: Fri Apr 13, 2007 10:34 am
Location: Ashland, Ohio

Re: Why does the idle dip when I come to a stop?

Post by occasional demons » Thu Jul 26, 2018 7:45 am

The higher the octane, the slower the fuel burns. The only way higher octane makes more power, is if it has something to work with: Higher compression, and more spark advance.

To exaggerate things a lot, if the octane is high enough, the fuel will still be burning as it goes out the exhaust valve. You would be making less power, and eventually melt your exhaust valves. Too low, and combustion will be complete before the piston and rod has traveled enough to put the right leverage on the crank.

The higher octane would affect higher RPM more than idle, since it has more time to complete combustion at idle.
- Bill

desmodromic wrote:You have to remember what's important here, while they make New humans everyday, they'll never make another Neon.
Skellibert wrote: Fri Oct 13, 2017 3:42 amThis is a daily by the way, not a track car or fun buggy.

HottRodd
Neon Enthusiast
Posts: 995
Joined: Thu Feb 25, 2016 7:11 pm
Location: Brossard, Quebec, Canada

Re: Why does the idle dip when I come to a stop?

Post by HottRodd » Thu Jul 26, 2018 6:07 pm

What I find strange is idle is fine when I start (720 rpm) and is always good when in neutral or park . Only when I come to a stop it goes down to 600. . I'm going to try my spare IAC to see what the difference is . As far as the ambient air temp sensor goes , what would be an average reading with the motor heated up , I mean outside vs inside difference? I'm sure I'm grasping at straws . I can't seem to find anything wrong to cause this . How about the torque converter. Can it become unbalanced. Is it that either it works or it doesn't. ..... is there a middle ground. Does anyone make "THE BETTER TORQUE CONVERTER " IF my crankshaft was say a little unbalanced would there be signs say like my accessory pully would spin with a little wobble. Would it show?
The 2003 2.0sx guy, 30k original miles :dance:
30k is that possible, Yeah :good: :

occasional demons
Master Neon Mechanic
Posts: 11367
Joined: Fri Apr 13, 2007 10:34 am
Location: Ashland, Ohio

Re: Why does the idle dip when I come to a stop?

Post by occasional demons » Thu Jul 26, 2018 6:40 pm

Ambient temp sensor will be very close to the ambient air around the car with the engine running. It will rise if the engine is at operating temps, and the engine is shut off.

The incoming air keeps it pretty close to ambient, due to it's location before the air filter. On the 1st gens, the air intake temperature sensor is in the IM. In this case, the reading would be higher both running, and off. The IM is usually warmer due to the closeness to the engine, and the air passing through the radiator. An aluminum IM would be even warmer, due to better thermal conductivity.

The only thing a TC could do to impact in gear idle, would be if it failed and the stall speed became much lower. You would know something was wrong, because the car would want to move without any throttle input, as in "having to stand on the brakes" move.

If the rotating assy was out of balance, you would have specific vibrations at specific RPM(s). it would be both in gaining and losing rpm at the same point(s).
- Bill

desmodromic wrote:You have to remember what's important here, while they make New humans everyday, they'll never make another Neon.
Skellibert wrote: Fri Oct 13, 2017 3:42 amThis is a daily by the way, not a track car or fun buggy.

Post Reply

Return to “2nd Gen”

Who is online

Users browsing this forum: No registered users and 2 guests