07 Taurus 3.0l Vul Thermistor
spark802
12-05-2009, 02:51 PM
I had some welding done on my car. The battery was dis-connected, but the fuse to the ECU wasnt removed. I now have idle problems showing up because of the colder weather. I have a rough, coughfy sort of start and then the idle goes from 1100 rpm to 1800 rpm and then settles down. I am told my thermistor is shot. What are long term effects if i dont change it out right away?
shorod
12-05-2009, 10:51 PM
Welcome to the forum!
Who is telling you the varistor is shot, and which one are they talking about? How long does the idle stay at 1800 rpms, and when it settles down what does it settle to? Based on what you've typed above I don't necessarily know that you have a concern. If the idle speed settles within several seconds of starting it, or as soon as you shift out of park, that doesn't see all that abnormal.
Was the person who told you the varistor is shot referring to the Intake Air Temp (IAT) sensor, the Coolant Temperature Sensor (CTS), Mass Air Flow (MAF) sensor, or other?
I doubt that the welding had anything to do with the issue, unless the welding was very recently and the computer has not yet completed its drive cycle due to the battery being disconnected.
-Rod
Who is telling you the varistor is shot, and which one are they talking about? How long does the idle stay at 1800 rpms, and when it settles down what does it settle to? Based on what you've typed above I don't necessarily know that you have a concern. If the idle speed settles within several seconds of starting it, or as soon as you shift out of park, that doesn't see all that abnormal.
Was the person who told you the varistor is shot referring to the Intake Air Temp (IAT) sensor, the Coolant Temperature Sensor (CTS), Mass Air Flow (MAF) sensor, or other?
I doubt that the welding had anything to do with the issue, unless the welding was very recently and the computer has not yet completed its drive cycle due to the battery being disconnected.
-Rod
spark802
12-06-2009, 12:02 AM
Hello Rod,
Thank you for replying. The person that gave me this info is currently my instructor, i am in my secound level as a highway trailer tech. He has been in the automotive/truck and transport/ heavy duty a long time. Other than that i am in a colder part of the continent here. Winnipeg Canada to be precise. As far as the welding goes i had a welding shop install a hitch for a bicycle rack so i'm not even a 100 percent sure they did any welding. The starting air temps now are around 20F. I havent had the rough starting until the cold air temps began. It should start better. When it first fires in the cold weather it stuggles to catch to a normal idle. It then creeps up to 1100 rpm and spikes to 1800 rpm for about 30 secs. Then it settles back down. When ive been driving around for a while it starts up good and idles ok. He didnt tell me anything about varistors. He called it a thermistor. So i cant readily answer your question about type of varistor. From what you've said about different sensors involved i would say it would be the CTS. I know something about ECUs and sensors from the trade i am in but these other things are new to me. My actual concern is the way it struggles to start when cold. My owners manual has a reset procedure which i follwed and that didnt change anything. Anyway hope i didnt ramble on too much.......Dave
Thank you for replying. The person that gave me this info is currently my instructor, i am in my secound level as a highway trailer tech. He has been in the automotive/truck and transport/ heavy duty a long time. Other than that i am in a colder part of the continent here. Winnipeg Canada to be precise. As far as the welding goes i had a welding shop install a hitch for a bicycle rack so i'm not even a 100 percent sure they did any welding. The starting air temps now are around 20F. I havent had the rough starting until the cold air temps began. It should start better. When it first fires in the cold weather it stuggles to catch to a normal idle. It then creeps up to 1100 rpm and spikes to 1800 rpm for about 30 secs. Then it settles back down. When ive been driving around for a while it starts up good and idles ok. He didnt tell me anything about varistors. He called it a thermistor. So i cant readily answer your question about type of varistor. From what you've said about different sensors involved i would say it would be the CTS. I know something about ECUs and sensors from the trade i am in but these other things are new to me. My actual concern is the way it struggles to start when cold. My owners manual has a reset procedure which i follwed and that didnt change anything. Anyway hope i didnt ramble on too much.......Dave
spark802
12-06-2009, 12:07 AM
And by the way when the idle does settle down it sits around 800-900 rpm. Which sounds and feels normal. I am thinking thats what it should be at start up as opposed to the roughness.
shorod
12-06-2009, 09:38 AM
Oops, I typed "varistor" but was thinking "thermistor" per what you had typed.
I don't really think the cold start scenario you describe is abnormal. Typical cold starts to involve a higher idle, and as long as the idle drops when you shift out of park I think it's probably functioning about as designed. If the IAC was not operating you would not have a high idle and you would probably have a lot of difficulty even getting the car to start and stay running when cold, or when using the A/C, heavy electrical load, or have the steering wheel turned to one of the full lock positions. If the fuel economy is about what you would expect then I doubt the IAC is faulty, and probably the CTS is not too far off, if at all. When the car is idling, either high or normal, is it smooth or is there roughness to it? Have you completely checked the vacuum lines, spark plugs and plug wires or performed a tune up recently?
The CTS are known to have issues and, somewhat like the Oxygen sensors, are not really bad to change out regularly. A properly working new CTS (like oxygen sensors) will certainly not hurt the fuel economy and likely make a slight improvement. There have been posts on this forum suggesting you should get the all brass CTS, some of the less expensive ones don't seem to last.
I'd also suggest that you spray out the throttle body, check the air filter, and if you're feeling adventurous, remove the IAC and spray it out along with the passages. Just be careful not to lose the gasket when removing the two bolts holding the IAC to the throttle body. If a tune up hasn't been performed recently, consider that as well.
As for installing the trailer hitch, it's doubtful any welding was performed. Most nowadays do not require any welding. They may require some drilling, but not welding.
Also, don't reset the PCM unless you are trying to remedy diagnostic code issues. The PCM has to go through a drive cycle everytime it's reset. The car may run oddly while the PCM is completing the drive cycle, so if you're trying to solve an idle speed concern, continually resetting the PCM will only make that more difficult.
-Rod
I don't really think the cold start scenario you describe is abnormal. Typical cold starts to involve a higher idle, and as long as the idle drops when you shift out of park I think it's probably functioning about as designed. If the IAC was not operating you would not have a high idle and you would probably have a lot of difficulty even getting the car to start and stay running when cold, or when using the A/C, heavy electrical load, or have the steering wheel turned to one of the full lock positions. If the fuel economy is about what you would expect then I doubt the IAC is faulty, and probably the CTS is not too far off, if at all. When the car is idling, either high or normal, is it smooth or is there roughness to it? Have you completely checked the vacuum lines, spark plugs and plug wires or performed a tune up recently?
The CTS are known to have issues and, somewhat like the Oxygen sensors, are not really bad to change out regularly. A properly working new CTS (like oxygen sensors) will certainly not hurt the fuel economy and likely make a slight improvement. There have been posts on this forum suggesting you should get the all brass CTS, some of the less expensive ones don't seem to last.
I'd also suggest that you spray out the throttle body, check the air filter, and if you're feeling adventurous, remove the IAC and spray it out along with the passages. Just be careful not to lose the gasket when removing the two bolts holding the IAC to the throttle body. If a tune up hasn't been performed recently, consider that as well.
As for installing the trailer hitch, it's doubtful any welding was performed. Most nowadays do not require any welding. They may require some drilling, but not welding.
Also, don't reset the PCM unless you are trying to remedy diagnostic code issues. The PCM has to go through a drive cycle everytime it's reset. The car may run oddly while the PCM is completing the drive cycle, so if you're trying to solve an idle speed concern, continually resetting the PCM will only make that more difficult.
-Rod
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