Stock PCM

[xtremeskier97]

I've been searching but cant seem to find the answer.

If I'm just removing the PCM to replace the valve cover gasket, will I have to do any relearn after reinstalling it?

 

[jimmyjam]

No. Some learned parameters will reset but it requires no intervention on your part

 

[Wooluf1952]

No. Some learned parameters will reset but it requires no intervention on your part

But if your throttle body is dirty, you'll need to clean it or the engine will run rough for a while because of disconnecting the battery.

 

[xtremeskier97]

My engine has been running rough already at idle. That is why I was going to replace the valve cover gasket (thought there was oil on the plugs). Turns out there isnt, so I didnt need to replace the gasket or disconnect the PCM.

What else could be causing such a rough idle? Things I've done/checked:

1) The throttle body was not that dirty, but I went ahead and cleaned it anyway since I was there already.

2) The plugs looked good. Gaps in spec (replaced them with 14-103s about a year ago or so). No oil on the thread or coil side.

3) I've taken the belt off and run the engine for a few minutes and it's still rough idle.

4) Checked if rough idle is in P, D, or R. It's rough in all. If I'm at a light I can throw it in N and it smooths for a split second but gets right back to rough.


I dont know what else to check. I'm tired of it feeling like my truck is gonna shake apart.

Any ideas?

*EDIT* I was thinking about replacing the O2 sensors because they have never been replaced since I've owned the truck (about 3 years). Should I replace the up or downstream first? Also, which is the one right behind the oil dipstick? I can only do 1 right now as money is tight from paying taxes.

 

[spearman]

maybe dirty.

 

[xtremeskier97]

maybe dirty.

I've never replaced that either. Where is that located?

 

[ScarabEpic22]

First off, PLEASE tell me you DIDNT gap/try to gap your plugs! The AC Delco stock ones are iridium plugs, you CANNOT adjust the gap and if you try to, you will ruin the plug.

Does it misfire or just feel like it's shaking? Id do a compression and/or leakdown test next then look at motor mounts. Our mounts are hydraulic filled and are known to wear out, when they do the engine rocks side to side more, especially at idle.

My 02 is rough at idle and I know it'd the motor mounts, they've been slowly dying for the last 2+ years and it's pretty bad now. Looks like when I do my header install, it's going to get new motor mounts too.

 

[xtremeskier97]

No I didnt gap them. I just checked the gap to make sure it was still in spec.

I havent looked at the motor mounts. Perhaps I should compression test first. I'm pretty sure I have a gauge. If not, my brother-in-law does.

 

[gmcman]

Hook a vacuum gauge up to this port and post the results, ie, steady or fluctuating needle, and how much vacuum expressed in in/Hg.

Over 80K miles is a good time to replace upstream O2 sensor, the one near the dipstick.

Any codes?

Did you use the dielectric grease on the tip of the plug that contacts the coil?

What RPM is the roughness? If at or very close to 600 then I would suspect the mounts as well.

 

[gmcman]

Disclaimer: That is NOT , my dirty A&$ engine.

 

[Mypetropig]

I've never replaced that either. Where is that located?

Its on the inside frame rail just below the drivers door. Also if you havent done so, run some injector cleaner through it. I believe Advance Auto has Chevron w/techron on sale as buy one get one for about $9, its the one that treats 20 gallons. Its been noted as one of the better cleaners.

 

[Sparky]

Disclaimer: That is NOT , my dirty A&$ engine.

lol looks almost like mine right now
(mine isn't quite that bad as I did wipe some stuff down recently)

 

[Wooluf1952]

The up-stream O2 sensor is the one behind the oil dipstick. It's the one that tells the PCM to enrich or lean out the fuel mixture.
The down stream O2 sensor is after the cat.
The up-stream is the one that normally needs changing.