95 Eclipse RPM cycles during idle hot

[Jim_S]

I am working on a:

1995 Mitsubishi Eclipse, 2.0 liter

When cold, the car idles nicely.

As it warms up, the idle RPM cycles up and down.
As it warms up, the amplitude on the upside increases.
Say the cold idle RPM is 800. As it starts to warm,
the idle RPM will cycle between 800 RPM and 1000. Then
this increases steadily to between 800 and 1200, and
keeps increasing. Eventually the upside RPM gets over
4000 RPM at idle.

The length of an up-down cycle is only a couple of
seconds.

While all this is happening, can see on the scan tool
that the idle air controller (IAC) is cycling up and
down. But other PID's look normal.

Also the MIL comes on. But the cycling begins first
and the DTC's are not set until the upside RPM is well
over 1500. The DTC's are:

P0340. Camshaft Position Sensor A Circuit Malfunction
P0505. Idle Control System Malfunction
P0352. Ignition Coil B Primary/Secondary Circuit Malfunction
P0351. Ignition Coil A Primary/Secondary Circuit Malfunction
P0113. Intake Air Temperature Circuit High Input
P1294. Manufacturer specific code

Have already replaced IAC motor, cam sensor, and ECM. The
problem still persists. Also temporarily disconnected
the PCV hose. Have checked for vacuum leaks and found
none. Spark plugs and wires are reasonable new. The
problem still persists.

Removed and reinstalled the crankshaft position sensor (CKP).
Did not replace it yet, because cannot keep on paying for
new parts and get no results. The CKP had oil splashed on
it when it came out. Is this normal, or the symptom of a
problem?

Has anybody seen this problem before and know the cause?

Jim S.

[david-b]

Hi Jim;

Firstly, what model are we talking about? Non-turbo or turbo? On the turbo models, there's an idle adjectment that may be bad or needed to be tweaked.

Have you checked the TPS? The TPS can cause some weird problems like that, althought the IAC would seem like the problem, but I see it's already replaced. Was there any difference at all when you replaced the IAC? If you unplug the IAC, is there any difference?

Something else to check is the actual throttle body. Maybe the butterfly inside is stuck open just slightly enough to be causing excess air to come in, bypassing the IAC. Sure the IAC will still work, but air may still be coming in. That's almost a long shot, but check if it's sticking or dirty, and make sure it's solid and tight fiting.

And last but not least from me, make sure all the wires are good. When I did my head swap I had bad idle because the EGR pipe decided to rub against a loom with the wires to the IAC and TPS and melt the loom and the insulators, and then basically short out the whole system. Just a recommendation.

You seem to know what you're doing and talking about so I'm sure you'll find it. You'll get more responses later when more people get on here. Good luck!

[SilvrEclipse]

Wow, This is probably one of the best post I have seen in a long time. Very descriptive. Sorry that I dont have any answers for you but I'm sure someone can help you.

[Jim_S]

SilvrEclipse

Thank you for your vote of support. I was not trying
to win any prizes for the best post. I just wanted
others to have the information they needed to help me.


david-b

Thank you for all your good suggestions. But the
problem has been solved. We tried a new crankshaft
position sensor (CKP) and that fixed the problem.

Jim S

[david-b]

Glad to hear it works now. Good luck!

[TalonEclipseMixGsx]

Damn crank sensors. My neighbors eclipse just had one of those go out in his car. It started out by just stumbling in the higher RPM's, so we thought it was a boost leak. A few days later he stalled out and it wouldn't start back up. Wasn't getting any spark or fuel.

We messed with it for a couple days, changing out coils and other ignition parts, before getting the idea to check the cam and crank sensor. Unplugged the one on my car, and it did the same thing. We hooked up the data logger (even though it wasn't throwing a CEL) and it came up with a crank sensor.

If we would have just hooked up the scanner in the first place we would have saved ourselves a few days worth of aggrivation. But where would the fun be in that?