[Doom4life]

I'm trying to figure out why my 4.7L in my '02 Dakota seems to randomly race to 2,000 RPM's when its first started. It stays there for about half a second before dropping to 1600 RPM's (When it starts normally, this is where it usually starts at). As an example (I'll try to get a video up next time it does it), it starts so quickly its like someone is revving the engine. It also doesn't seem to matter what the outside temperature is as it has done it when its been around 0 degrees Celcius, 12 degrees celcius, etc.

I have replaced the IAC motor twice (once was a defective SMP part which was replaced with a Mopar part) due to a different starting and idling issue so that can be thrown out.

I know the intake air temperature sensor isn't reading right (sensor showed 18 degrees Celcius when it was 5 degrees Celcius outside), but what could be causing this? Aside from the starting issue, there are no other issues which I would assume would rule out a faulty TPS.

 

[trevor]

I'm not entirely sure, but it may have something to do with a vacuum leak. If I remember right, same think was happening with my grandpa's LHS (3.5l) and it had a cracked vacuum line.

 

[Doom4life]

What a quick reply! No vacuum leaks as I checked over all lines thoroughly while trying to diagnose a seperate issue.

 

[Doom4life]

Should also mention that I thoroughly cleaned the throttlebody last August, so that wouldn't be an issue.

 

[Doom4life]

So I posted some videos on YouTube. Although one was taken at night and the other was taken during the day, the temperature difference is only a few degrees Celcius, so I doubt that would affect anything.

A normal start
Engine racing

With the video taken at night, I specifically lifted the gas pedal to make sure that the cable isn't sticking. However, it still raced when it started. As I mentioned on YouTube, this is one is more of the minor starts, but it will also race up to 2,000 RPMs even quicker than what was shown in the video.

I'm wondering if this could be an issue with the TPS. Is there any other component that would affect starting?

EDIT: For the videos, turn up the sound a bit and observe how the engine sounds different between the two starts.

 

[Guest]

Wife's '02 Jeep GC did exactly the same thing. Replaced the TPS and problem solved.

 

[Doom4life]

Wife's '02 Jeep GC did exactly the same thing. Replaced the TPS and problem solved.

I put in the new intake air temperature sensor yesterday, but I have a feeling it is the TPS as I doubt the sensor would cause starting issues.

I'm going to order one just to be on the safe side, as I have a weekend out of town trip coming up and I dont really want it to get worse.

 

[modain]

When the TPS recently went bad on my Dakota it idled at startup very high, similar to your experience. Replaced it and all was well.

 

[Doom4life]

Thanks for all the posts on replacing the TPS. As I mentioned in my last post, I ordered a TPS from a USA dealership (Canadian dealerships charge anywhere from 150% to 200% more for the same part that I can get driving 20 minutes to an American dealership).

I did change out the IAT sensor, and it so far hasn't raced when started, but it was always so random so I doubt that did anything aside from giving the PCM more accurate temperatures.