Intermittent No/Difficult Start

ubertalldude · Post by **ubertalldude** » Mon Dec 02, 2013 9:10 pm

I've been doing some research online, but Google takes me to the same sites over and over again and my issue seems to be a little off from any other descriptions, so I'll ask politely for any advice, knowledge, or tips any users have on this matter.

Background: I changed the camshaft position sensor (BWD #CSS34) one week before the first incident in attempt to fix a low idle. It did not change the engine's behavior. I also parked under a tree overnight before both incidences and may have gotten rained on as well; wet leaves were in/on the cowl below the windshield before the conditions below manifested.

ISSUE: 2003 Dodge Neon 2.0 SE (ATX) w/101k miles has exhibited the following failures on 2 separate occasions now:

1st instance:
-car cranks, but fails to start as quickly as I normally expect
-I let off the ignition before the engine starts expecting for it to have already started (force of habit)
-the car does not crank, then throws DTC p0129 & p0340
-the car will no longer start after several cranks/seconds of cranking
-clearing the codes with an OBDII scanner does not aide the condition

This all occurred the Tuesday after a weekend during which I drove 400 miles total, all interstate. The first time it happened in a parking lot, so I left it to sit overnight. The following day I returned and the car started regularly on the first try. This was 2 weeks ago.

The second time it happened was Sunday evening after driving 140 interstate miles the preceding Saturday night:

2nd instance:
-car cranks, but fails to start as quickly as I normally expect
-I let off the ignition before the engine starts expecting for it to have already started (force of habit)
-the car does not crank, then throws DTC p0129
-the car will no longer start after several cranks/seconds of cranking
-clearing the codes with an OBDII scanner does not aide the condition
-removing the battery and reinstalling after 60 seconds does not aide either
-removing the battery for 20 minutes doesn't help, either
-cranking the car incessantly and mashing the gas DOES get the car to start
-I scan again after the car is running and observe p0340 reappears

After the car started I proceeded to drive it 130 miles home. The car stumbled a few times after returning to idle, but evened out immediately and idled fine. Additionally, when going from 1/2 throttle (maintaining speed) to 1/10th throttle or less (in order to decelerate) the engine would buck wildly and seemed to be jumping between normal power output and engine braking mode. When the throttle was released fully the engine would maintain top gear but engine brake very hard.

p1029 is "barometric pressure out of range"
p0340 is "Camshaft Position Sensor Circuit Malfunction"

After much research and thought, I'm thinking any one of combination of the following might causes:
-letting off the ignition before starting causes the p0129 (known to be a common cause of the code appearing) and the PCM stops sending the 5V bus to the cam sensor and the MAP sensor
-new cam sensor is intermittent/defective and shorts the system after a long drive then sitting for a night, thus bugging the PCM out and shorting that circuit and possibly the common bus with the MAP
-some wiring/connector is dirty/loose/worn/overheating/getting wet and shorting the pair of circuits
-my PCM is overheating on these long trips and doesn't manifest symptoms until the next day
-my PCM is faulty

After the next day and a healthy start the car continues to start/run/drive fine and the codes clear according to the engine's protocol (usually 3 good starts & warm-ups)

I'm not worried about it right now, as the condition is intermittent and appears only to be electrical in nature. Thank you in advance for any and all of your help!

Post by **occasional demons** » Mon Dec 02, 2013 11:41 pm

occasional demons wrote:When you changed the CPS, did you clean the target magnet off? (Gray lines) If that doesn't fix it, you may need a new target magnet. You can also try removing the MAP sensor, and cleaning it with some brake clean or similar to flush out any oil/gunk that may be plugging it.

I can't say I've heard of letting off the ignition before starting causing the p0129 code before. I generally crank mine just enough for it to catch and have never had that issue. I do not have an NGC PCM tho. Mine is SBEC. The overrun clutch on my starter rarely sees any use.

ubertalldude · Post by **ubertalldude** » Wed Jan 22, 2014 8:04 am

I finally found a complete fix for this issue:

Since the trouble all started when I replaced the camshaft position sensor I decided to try and reuse the OEM sensor that was originally on my car, so I bought a new camshaft sensor seal, installed it, and reinstalled the OEM/Mopar sensor from the factory line and now I've had no problems in over a month.

Lesson learned: Mopar ECU/PCM's don't like aftermarket sensors, and there's no need to replace a sensor that isn't broken.

MichNeon · Post by **MichNeon** » Thu Jan 23, 2014 1:43 pm

Have you checked the pins in the cam sensor connector? If the tabs in the pins spread, they would cause an intermittant connection issue. I went thru the cam sensor issue myself last year, and wrote a post which is now a sticky on the Neons.org 2nd gen forum. The title is "Cam sensor problems". It deals with the two cam sensor codes, and has a lot of info on the issues regarding cam sensor issues.