Allpar Forums banner
1 - 20 of 21 Posts

·
Registered
Joined
·
78 Posts
Discussion Starter · #1 ·
I have a 96 New Yorker with the 3.5 and 92k miles. The car would always idle around 1000 rpm if i drove it for 2 minutes or 2 days. Now when i start it cold it'll idle at 1000 rpm but after it warms up it's around 1500 and won't drop back down. If i let it sit a few hours it's back at 1000 but back up to around 1500 when warm and it used to always drop back to 1000 no matter how long it ran.

I changed the PVC and hose that looked rough but no difference. I took out the iac motor to clean it but that and the housing were very clean and one of the torx bolts was a hex so I'm thinking this was replaced by the previous owner or someone. It's kind of annoying at a stop because it feels like it wants to go with the brake on because of the higher idle when warm.

No check engine light or dash codes. Any ideas or suggestions are much appreciated.
 

·
Super Moderator
Joined
·
32,516 Posts
This is typically either a bad AIS, a vacuum leak, or someone has misadjusted the mass air flow screw that looks like, but is NOT, an idle screw on the throttle body. Since it changed during your ownership, it's probably not the latter.
 

·
Super Moderator
1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
Joined
·
22,020 Posts
This car has the dual throttle bodies?
If someone has tampered with the minimum air screws, it may need a dealer to set them correctly.
A non-OEM PCV may have too much air flow (like a vacuum leak), which would raise idle speed.
Did this fast idle happen out of the blue, or is there a history?
 

·
Registered
Joined
·
78 Posts
Discussion Starter · #4 ·
I appreciate the information. I can say with complete certainty the screws have not been touched or adjusted. When this started a few weeks ago i looked at every line, hose, fitting and connection i could see and trace. The PVC hose was collapsed almost flat so i changed that and the PVC. No difference. The motor itself was very clean and not gummed up but from the 2 different screws someone had it out before and not since I've had it. I'm the second owner.

There is a pattern to this since it started a few weeks ago. When i start out cold and come to a stop the idle drops back down. After it warms up the idle stays high. If i stop somewhere for a few minutes or so the idle will be high. If it has a chance to cool down for a few hours the idle works correctly but after it warms the idle stays high. Up until this started a few weeks ago i could drive it for hours and come to a stop and idle would drop back to normal. Now after the engine gets warm the idle stays high.
 

·
Registered
Joined
·
4,922 Posts
. . . There is a pattern to this since it started a few weeks ago. When i start out cold and come to a stop the idle drops back down. After it warms up the idle stays high. If i stop somewhere for a few minutes or so the idle will be high. If it has a chance to cool down for a few hours the idle works correctly but after it warms the idle stays high. Up until this started a few weeks ago i could drive it for hours and come to a stop and idle would drop back to normal. Now after the engine gets warm the idle stays high. . . .
When the engine is cold the engine fuel management system runs in OPEN loop mode. The PCM (powertrain control module) does NOT use the signal from the oxygen sensors. I believe it has 2 upstream and 2 downstream oxygen sensors. When the engine warms sufficiently the PCM goes into CLOSED loop mode and reads the signal from the oxygen sensors. I would suggest using a scan tool and compare the short term and long term fuel trim values between bank 1 and bank 2. If there is significant differences then look at the bank with the skewed value for an intake leak.

I believe the intake plenum on that engine is plastic and when the engine is cold there is no leak. But as the intake warms ups, a small leak develops and the extra air leak is leaning the air - fuel mixture on that bank. The engine controller compensates and adds additional fuel on that bank to bring the air fuel mixture to stoichiometric balance and that raises the idle.
 

·
Registered
Joined
·
3,075 Posts
you either have an air leak or a bad ais.
 
  • Like
Reactions: KOG

·
Super Moderator
1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
Joined
·
22,020 Posts
Being a 1996, it is OBDII which means that generic OBDII scan tools should be able to communicate with the PCM through the underdash link connector.
You might want to use a capable scan tool to look at 'target idle' and compare it with the actual RPM. If the PCM can't bring idle speed down to target and the IAC (idle air control) motor is almost closed (no or little air flow), then I would suspect an intake manifold vacuum leak or a throttle blade isn't closing properly.
The TPS (throttle position sensor) should be about 0.65 volts give or take at closed throttle. It shouldn't jump around and should have a smooth progression in voltage as the throttle is opened (you can do this with the engine off, ignition on).
The MAP sensor measures intake manifold vacuum (negative atmospheric pressure) and should react inversely with the TPS.
Write down any sensor readings that seem unusual or note any abnormalities. It helps if someone familiar with 'good' readings is present to help out.
 

·
Registered
Joined
·
78 Posts
Discussion Starter · #8 ·
For starters i appreciate all the information. I haven't been able to get any scan tool to read on that car for a while. They work on everything else. That's another problem i need to resolve. The car has 92034 miles. At 62486 miles i replaced the intake manifold and intake plenum gaskets. I know the intake is aluminum, the plenum I'm not sure if its aluminum or plastic. When i get some time next week i got mirrors with extension handles and i thoroughly check every line.

I'm figuring on spraying around the plenum after it warms up and see if the rpm changes and even try re-torquing the bolts since i went out and got an inch-pound torque wrench when i originally did the gaskets. I could probably even change the plenum gasket again. That wasn't hard or expensive. The intake manifold gaskets were another story. After that I'll change the motor and post the results. I most certainly appreciate the information.
 

·
Registered
Joined
·
4,922 Posts
. . . . I haven't been able to get any scan tool to read on that car for a while. They work on everything else. That's another problem i need to resolve. . . . .
When you connect a scan tool through the OBD II diagnostic port, the tool expects there to be 12 volt power on pin #16. Check pin #16 for power. See attached image.

Diagnostic Data Connector OBD II.gif
 

·
Registered
Joined
·
78 Posts
Discussion Starter · #10 ·
I certainly appreciate the information. Hopefully this week i can look at the high idle. (Just not enough days in a year). I was thinking a fuse might be the problem for the data connector but could never find a fuse listed for it for that car, either the inside panel or under the hood.
 

·
Super Moderator
1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
Joined
·
22,020 Posts
The fused 12 volts at the DLC is shared with other components. Does everything else work electrically?
A good DLC ground is just as important to power up the scan tool.
Does a scan tool not power up? Or does it power up and just not communicate with the vehicle?
 

·
Registered
Joined
·
3,075 Posts
You can take a piece of thin hoose and use as a stetoscope, a vacum leak is quite noisy if you manage to put the hoose in its vincinty.
 

·
Registered
Joined
·
78 Posts
Discussion Starter · #13 ·
My original post on the high idle has become a 2 part, the idle and the data link connector. As for the connector i checked pin #16 with 2 different test lights and they both light with the engine off. Didn't try it running. All the accessories work. Used a cheap tool and a better one, won't communicate.
 

Attachments

·
Super Moderator
1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
Joined
·
22,020 Posts
Being an older system, I don't know if either of those scan tools can speak the CCD bus language. Do you have instruction manuals for them and do they mention application limitations?
I remember some scan tools would not talk to a 25 year-old computer, only the DRBIII with the SuperCard did. Nowadays, the dealer uses a DRB 'emulator' software for the WiTech2 to diagnose these old buggies.

Vehicle Communication:
The system consists of a combination of modules that communicate over the CCD (Chrysler Collision Detection multiplex system) bus. Through the CCD bus, information about the operation of vehicle components and circuits is relayed to the appropriate module(s).
Each module receives the same information about a component or circuit as the other modules do. This significantly reduces the complexity of the wiring in the vehicle and the size of the wiring harnesses.
The Chrysler Collision Detection multiplex system (CCD bus) consists of a twisted pair of wires. These wires run from one module to another. They receive and deliver coded information between the modules. The information is coded to identify the message as well as the importance of the message.
When there are multiple messages trying to access the CCD bus at one time, the code determines the message that has higher priority, which is then allowed to access the bus first.
The two wires (D1) and (D2) of the twisted pair that make up the CCD multiplex system are called “bus +” (bus plus) and “bus -” (bus minus) respectively. Each wire has a measurable voltage level of roughly 2.5 volts.
In order to maintain the 2.5 volts on each line and provide a means of transportation for the coded messages, there is a “voltage divider network.” This network consists of some modules with bias and some with termination.
Bias is the part of the voltage divider network that places both bus+ and bus- at 2.5 volts. Termination in the circuitry is required to complete the voltage divider network and also to provide some electromagnetic protection for the bus.
NOTE: Communication over the bus is essential to the proper operation of the vehicle’s on-board diagnostic systems and the DRB. Problems with the operation of the bus or DRB must be corrected before proceeding with diagnostic testing. If there is a problem, refer to the Vehicle Communications section in this manual for diagnostic and repair procedures.
 

Attachments

·
Registered
Joined
·
78 Posts
Discussion Starter · #15 ·
I most certainly appreciate the information and will read it. I don't think the problem is the tools talking to the older computer because these exact readers worked previously but this is something i always wanted to try and figure out. I need to get back to the original problem this week, the high idle because that one is annoying.
 

·
Registered
Joined
·
78 Posts
Discussion Starter · #16 ·
Finally got back to the original high idle problem. Checked all the lines and can't find a problem. I re torqued the intake plenum, all bolts still at 250 inch pounds. I sprayed the intake plenum with carb cleaner after it was warm with the red nozzle extension. Just about anywhere i sprayed the idle dropped. I also sprayed around the intake manifold and the idle dropped from spraying just about anywhere.

The car actually pushed some antifreeze out from the fill/overflow reservoir. I've driven it a lot this week and the antifreeze is ok anyway. The intake manifold and plenum gaskets have 27,000 miles on them. I used Napa gaskets when i did it. I'm now wondering if the gaskets are the problem. They've been fine for a few years and this high idle just started a few months ago and all at once. Advice is very appreciated since this wasn't fun to do the last time and wondering if this is the problem once again.
 

·
Super Moderator
1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
Joined
·
22,020 Posts
This recall # 790 is long gone, but I remember fuel rails going bad even after the recall was performed. The right side was the one that cracked and went rich. The fuel pressure regulator is also in the right rail.
https://testing-public.carmd.com/Tsb/Download/31952/080022dc80bc03b3

You don't have to spray carb cleaner. It may less deceptive and dangerous just by squirting the gasket area with plain water. The engine speed will drop when it sucks water in through an opening.

If it pushed out antifreeze after an extended idle while stationary, did the cooling fans kick on?
 

·
Registered
Joined
·
4 Posts
Finally got back to the original high idle problem. Checked all the lines and can't find a problem. I re torqued the intake plenum, all bolts still at 250 inch pounds. I sprayed the intake plenum with carb cleaner after it was warm with the red nozzle extension. Just about anywhere i sprayed the idle dropped. I also sprayed around the intake manifold and the idle dropped from spraying just about anywhere.

The car actually pushed some antifreeze out from the fill/overflow reservoir. I've driven it a lot this week and the antifreeze is ok anyway. The intake manifold and plenum gaskets have 27,000 miles on them. I used Napa gaskets when i did it. I'm now wondering if the gaskets are the problem. They've been fine for a few years and this high idle just started a few months ago and all at once. Advice is very appreciated since this wasn't fun to do the last time and wondering if this is the problem once again.
 

·
Registered
Joined
·
4 Posts
3.5 was known for intake manifold vacumn leaks around the 75,000 mile mark. Our 97 concorde went at 78,000. You mentioned you used Napa gaskets. I don,t know who their vendor for gaskets is right now but i have heard some troubling reports of a noticable quality drop off on some NAPA parts recently. Seems they did some price cutting on their vendors at least thats what i was told. If true too bad because i always thought their stuff was a notch above autozone oreilly etc.
 

·
Super Moderator
Joined
·
32,516 Posts
If you spray carb cleaner and the idle changes, it got inside, and there is a leak.
 
  • Like
Reactions: KOG
1 - 20 of 21 Posts
Top