QuestionHello,
To start, i have 2 vehicles, 95 ply Neon & 95 Dodge Neon. The Dodge lost a timing belt and bent all the valves. I purchased the 95 ply Neon to replace the other vehicle.
My problem is that when the 95 Ply Neon gets to operating temp. and fan turns on , the idle goes erratic. like a giant vac leak. When driven you lose power, backfires with very poor accel.
I have taken all the sensors from the Dodge,and throttle body, installed them on the Ply. I also replaced the EGR from the other veh. Blocked off port before installing, same problem.Fuel pressure at 49#. Replaced plugs,fuel filter,ign. coil,wires and wire harness and ign. from pcm to engine.I have checked back pressure, ok.
Scan ck. I have a code p0340-p0352-p0351-p0141-p0138p1294-p1391. Key on-off 3 times I have gotten codes 25-43 that I remember of. After all items were replaced I get only the P1294 code.I can only believe that the pcm may be at fault. The Dodge has part#pcm #05259602. The ply. 5289709. I cannot find a used one. Advanced Auto Parts lists over 60 pcm #. None match the Ply #.
I cannot think of anything else at this time. I am a retired auto mech. for 34 years.I do not like to replace parts, unless I am sure.I replaced all the sensors because it was just as easy to remove them from the other vehicle rather than ck each one individually.I have a scan tool, to evaluate sensor values. I did see anything abnormal.
Thank You,
Gary c McClaren
AnswerOK, so both are SOHC. The (c) code is for the SOHC, a (y) would be for the DOHC. So the pcm's interchange didn't help. I would suggest that you put an egr back on, just make sure that is it clean and the stem moves freely. I can't be certain that running without it will not impact normal operation. And I would have suspected it would have set a code when it was absent, no? Anyhow, see the second response below.
Hi Gary,
Without waiting for answers, just assuming the engines were basically identical to begin with, let me layout some observations about the 1294. It is saying that the idle control motor (IAC) is unable to maintain the idle speed in the desired range. That may be due to something other than the idle control motor given how poorly the engine runs off idle. So I wouldn't focus on the IAC yet.
Some possible causes:
an intake manifold leak is worth investigating with some spray shots of starter fluid.
the coolant temp sensor may be off-value (I would not expect the fan to come on so promptly as you described). It should read 700-1000 ohm at normal engine operating temperature. If that were "off-value" you might not have a proper mixture.
The fact that it acts up only at warm-up means that this begins when the engine is operating in closed loop, with all the sensors operational (as opposed to open loop during warm up, with some presets instead of sensor inputs).
How about the oxygen sensors conditions? Those don't come into play until closed loop operation. Have you checked the harness connections for both the upstream and downstream sensors? How about interchanging them as well from the spare engine?
Have you tried interchanging the pcm's? notice any differences?
Those are some idea to start with.
Are there any codes other than 55 via the check engine light?
Roland
Hi Gary,
Are both engines single or double overhead cam? Any reason why they would have different pcm's, equipment-wise? This is going to take some time to analyze and to be of help. Let me know by the "thank and rate" tab, where there is a space for comments, what the answers are to these questions. Then I'll send a follow up response to you without your having to wait for an "opening".
Roland
