Troubleshooting rough idle 95 PAU

[Schlotzky]

My 95 PA ultra has a rough idle with small but present stumbles randomly.

New:
fuel filter
air filter
spark plug (autolite plat)
plug wires
oil/sc oil
rotated a new coil through without any change

The only thing I can think of now is a vacuum leak, but would that cause a random stumble? Either way, I've done a visual check of everything multiple times and there is nothing obvious. Any places on the L67 that are prone to vacuum leaks, or anything else that could cause my condition?

[ZiggyPA]

Have you checked for codes?

[Schlotzky]

Isn't currently throwing any codes. It did once for just a second or two a month or so back when it got bad for no apparent reason. Will the codes be stored in memory? I have a friend that can read them if so.


Also, I'll note that I checked all the plugs and connections last night and all of them looked good, light brown in color.

[big white bufflo]

Some code are stored but most are erasted after a key cycle clean your idle air control that could be the source of rough idle or a miss fire bad plugs or wires there are some ideas

[Jrs3800]

No the codes are not erased after a key cycle... The SES light may go out but the codes are stored in the computers memory... You can actually have Current codes and History Codes with the 94-95 PCM's in these cars...

[C man]

Currently having the same issue mine is throwing a P0341&42 code, loss cam signal/ cam failure doesn't alway throw a code when it first starts to display symptoms like random missing. Mine threw a code about two months ago and has been getting progressivily worser. But doesn't usually set a code until the engine is warmed up most of the time. The warmer the weather gets the faster it starts to seem to miss. And it always goes away when you restart again until it goes threw another phase of acting up.

I'm now leaning toward a bad Crankshaft Position Sensor. Since I did see the RPM gauge flucuate up and down the other day and the car seemed like it wanted to stall.

BTW how many miles on your PA becuase some things commonly happen around a certian mileage range on 3800's from what I have observed.

[Schlotzky]

140,400 as of yesterday. Cleaned up the MAF but can't get the IAC off without removing the TB and TB gaskets are on backorder, so that will have to wait. I'm going to get the code read and I'm sure that should help with diagnostics, I'll post up again when I have the codes.

It was only bad once a few months ago when it set the code off, since then it has just been very very minor stumbling and rough when idling, and the occasional jump of 100ish RPMs down.

[Schlotzky]

Dang, there was a laundry list in the History. I've never had the codes cleared though, so who knows how far back this goes. I had a traction control issue when I bought the car that I resolved, and when replacing the BPMV, I left the IAT out for an engine cycle or two, but I don't remember it throwing a code.

P0113 IAT Sensor High
P0118 ECT Sensor High
P0132 H02S High Volt
P0341 Camshaft Crank Error
P0502 Vehicle Speed Sensor No Sig
P1571 Traction PW M Link

And these were found too, though I don't remember exactly where, not in the history but not current, don't ask.

P1573 (didn't write down description) google says: "pcm ebtcm data error"
P1650 QDM 2 Error

I can't draw any conclusions from this. Anyone?

[ZiggyPA]

The ones starting with 1 would be the history codes. I think they remain in memory as long as they are not cleared and the battery isn't disconnected.

[Schlotzky]

Which if any would be causing my symptoms?

Ziggy, so you're saying
P0341 Camshaft Crank Error
P0502 Vehicle Speed Sensor No Sig
aren't history, but the rest are?

Or just these are history:

P1571 Traction PW M Link
P1573 (didn't write down description) google says: "pcm ebtcm data error"
P1650 QDM 2 Error

[ZiggyPA]

Originally Posted by Schlotzky

P1571 Traction PW M Link
P1573 (didn't write down description) google says: "pcm ebtcm data error"
P1650 QDM 2 Error

These would be your history codes.

[Schlotzky]

Ok. So what do they mean? Every once in a great while (actually, only right after the codes are read for something, first ignition cycle) the traction off light will come on. So What would the other point to? What is ebtcm and qdm 2?

[ZiggyPA]

That's pretty much as much as I know about these codes. My book doesn't even list 0571 and 0573, 0650 is listed as "mailfunction indicator lamp, control circuit malfunction"
I guess your current codes are caused by aforementioned sensors which give odd readings once in a while. Which in turn could cause the stumbling.
Maybe someone with more experience with this will chime in.

[Schlotzky]

Originally Posted by C man

Currently having the same issue mine is throwing a P0341&42 code, loss cam signal/ cam failure doesn't alway throw a code when it first starts to display symptoms like random missing. Mine threw a code about two months ago and has been getting progressivily worser. But doesn't usually set a code until the engine is warmed up most of the time. The warmer the weather gets the faster it starts to seem to miss. And it always goes away when you restart again until it goes threw another phase of acting up.

I'm now leaning toward a bad Crankshaft Position Sensor. Since I did see the RPM gauge flucuate up and down the other day and the car seemed like it wanted to stall.

BTW how many miles on your PA becuase some things commonly happen around a certian mileage range on 3800's from what I have observed.

This is sounding more and more likely. My car acted up today, it was fluctuating rapidly and wanted to stall, missing really bad, but not consistently. Read the codes again today, and this is what popped up:

P1361 Ignition Control Toggle Error
P1650 QDM 2 Error

And in the real time monitoring datastream Cam/Crank Error showed as "1". The code description seemed to point toward crank position sensor, though it never actually said it.

QDM was longer ago in history, and I don't know what it means, but if it has anything to do with the traction control light, I think it might be unrelated. Like I said, after clearing the codes, the traction off light came on for on engine cycle, but has been fine since.

Anyone have any deeper insight to these codes? Anyone know how difficult it is to change the crank sensor? I was able to see it, but it looks like it might be a pita to change.

[big white bufflo]

the cam sensor is real easy its location is to the left of the water pump but the crank is not hard but it take some time remove pas tire ,remove splash sheild ,with impact remove harmonic balancer,you need a puller to pull harmonic balancer off ,remove plastic cover over sencor kind of take refrance on the position of sencor because there is a GM tool that is to be used to aligne the sencor but it can be done w/out by putting it on slightly lose then slide harmonic balancer on the aligne it to the balance the tighten it up . other idication of crank sencor going bad it when driving on the road the car like hicup the resume no trouble