1997 Suburban running rough

[nlewis59]

My 1997 Chevy Suburban idles very rough, but runs fine over 1200 rpm. Just changed rotor, cap, wires, and plugs. Check engine light on. Code say "Crankshaft misalignment". My son believes this indicates wear on the distributor or distributor gear. But driving it, I would think this is a vacuum tube issue as it seems to change when idling in N or in P. Idling in D is the worst.

Any suggestions will be greatly appreciated.

 

[zora]

what is the actual code? PXXXX?

 

[VanGo]

I'm guessing P0016
http://www.obd-codes.com/p0016

 

[Suburbanized]

Pull code before replacing anything...don't guess and throw away money at parts you don't know are broke.

 

[nlewis59]

Can't remember the code - but it referred to the camshaft position sensor CIRCUIT. I've learned this could be the CPS or "PCM" going out. Anyone else experience this?

Also, what is a PCM - I couldn't find its definition anywhere.

Many thanks,

Sixth Nephi

 

[Chuzz]

PCM is your power control module. Very rarely do they go bad. I don't know personally, but I THINK there's a way to check the crank sensor and cam sensor to see if they're working. I think you have to use a volt/ohm meter and check the resistance. Maybe a mechanic here can enlighten you. One other suggestion is to unplug your Mass Airflow Sensor and see if that makes any difference in the idle.

 

[nlewis59]

Chuzz, I unplugged the Mass Airflow Sensor and it seemed to make no difference in the idle, but I did see a new DTC pop up, with the P1345 (Camshaft/Crankshaft position). Does this tell me anything?

Thanks,

 

[nlewis59]

When I used my friend's scanner, I got P0340 Camshaft Sensor Position Circuit error. When I bought my own scanner (both Innova 3100) it gave me P1345, Crankshaft / Camshaft misalignment.

My paper manual says to use jumper wires to test the CPS. The ground circuit appears good. Is there any reason I can't just unplug the sensor and run the car to see if it makes any difference? If it idles just as poorly, wouldn't this indicate the sensor has failed; seems this would basically be simulating a failed sensor. Unless only "part" of the sensor is bad...

Disconnecting the Mass Airflow Sensor made no difference in the idle roughness.

Thanks for any suggestions.

 

[nlewis59]

The problem seems to have been at least partially resolved by replacing the camshaft position sensor (CPS). This resolved the P1345 DTC, though now I'm seeing one for "random misfires" on all cylinders. I'm hoping this will be resolved by cleaning the fuel injectors.

Added cleaner to the tank. Should that not work, can this be done manually?

Here are some pictures for replacing the CPS:

The first picture show the CPS wire harness (red arrow), the CPS (blue arrow), and the notch in the rotor plate (yellow star, rotor removed).

the second shows the notch moved to where it aligned with the CPS so that it can be removed. I moved the rotor plate by cranking the engine.

 

[VanGo]

Sure would help to know what codes you are getting. This still sounds electrical, not fuel related.

 

[nlewis59]

VanGO - as noted above, P1345 and P0340 were the codes I was getting originally. After replacing the CPS, though, these have gone away - now I see one for "random misfires" or "misfires on #6" (sorry, don't recall that code right now - I'll have to check it again and post it here when I get home).

While it's running much better with the new CPS, it still seems to have a poor fuel mix at idle, it idle RPMs are around 500 (too low?) dropping as low as 400 occasionally. But only at idle. Could this be the Idle Air Control sensor? Or the Intake Air Temp sensor? Or just dirty fuel injectors?

The plugs, wires, cap, and rotor are all new.

Thanks for any suggestions.