I posted this on the Engine Tech board, but maybe some of you V6 guys have some input.

I have a 92’ 3.1L. MPFI Camaro. A friend and I have been spending a few months trying to fix a rough Idle. The only time it idles rough is at a stop, in Park and in drive. The car runs fine otherwise, no lack of power, etc. This is what we have done so far.

1. Found 2 vacuum leaks. Fixed
2. Check Engine light came on, car was running lean, replaced the O2 Sensor.
3. Diode was starting to go bad in the alternator. Changed Alternator
4. Changed Spark Plugs, and wires (cap and rotor were good)
5. Checked Engine Compression. All but Cylinder #1, because we couldn’t get the compression gauge to go in.
6. Last but not least, we checked timing, its dead on.

I have had three codes in the past month (a month after Oxygen Sensor was replaced), Code 42, 44 and 45, (42)=EST (if it's EST, car wouldn't run, but It threw this code at first start up after battery disconnect), (44)=Oxygen Sensor (Lean) and (45)=Oxygen Sensor(Rich).
All I have to say is HUH???

So, if anyone has some suggestions on what to check next, it would be very helpful, as we are running out of ideas.

Thanks,

I was about to tell you to tap on your MAF sensor while the car idled to see if the engine jumps around- but I don't believe you have a MAF on that year car. If i'm correct you have a speed density sensor? I don't know how they work- never owned a car with one.

Me thinks....
Serious, you have ignition problems which is not completely burning fuel in your system & that's CAUSING the signals you receive.
Cause.
Check your timing chain for good tension?
When was it last changed?
Coil is original & weak?
Tune Up?
Good air flow to engine to help burn fuel?
I lost my igniton modular.
As I sat by side of road, I had fun.
Paperclip & download codes.
34 & 45 (I have a 1985 model year car).
Both deal in timing & igniton.
One good module installed & I ain't seen a code yet nor did I "clear" computer.
You are seeing the effects of the cause.
Try starting with "checking" your ignition system for max strength.
Good luck, it did it for me.

Well, acording to the Chilton manual I have an MAF Sensor, can this be checked like a module? Such as, taking it into a shop or auto parts store and have them test it?

I have had the car for 8 years, never even touched the timing chain, will check that. Also, call me ignorant, but how exactly do you "check" an ignition system?

Thanks again guys

Common sense...
Open hood at night time DARK, check for any lightening you see on wires, etc.
IF you see ANY you have a weak link.
IT COULD BE BAD PLUG WIRES arching.
Chain,
You remove the distributor cap
Put a 17mm socket on the crank, turn BY HAND.
IF crank moves YET distb. rotor does not, immediatly, you need a new timing chain.
After 50-75K miles, you do need a new one anyway.
You only need move crank (any directon) by about 2-4 inches for this test
Coil.
Original, it is possibly weak. An aftermarket one will return HIGH OUTPUT spark for about $30-40
New plug wires, correct heat range spec plugs all create a stronger spark to burn the fuel.
The other stuff, I "replace" for testing.
IF it makes no true difference, I just return it & argue!
Serious, I know not a test for the MAF/MAS stuff.
Module, if your car runs, it's good.
Common sense will assist ya a bit in this part of the fun search.
I think you are not burning all the fuel you use, that's all.
Change sensor AFTER you eliminate all the other stuff.
Why "season" a new Oxy Sensor with wasted fuel?
Install that when ya believe you have eliminated all other varibles.
Again, when my ignition module died, it was obvious I had lots of left over fuel out the tail pipe, so I accepted the ECM test answers.
Hope this is clues.
The chain is a mission that will return the BEST results of almost all this stuff.
AND IF YOU DECIDE THE T CHAIN TO REPLACE,
you ALSO should replace the tensioner in the t chain area & water pump and install a new balancer sleeve. This ALL eliminates alot of varibles for a few pennies more as they parts are now in your hands.
All these parts are removed when your replace the T chain.
T chain is $30-ish, W pump is $20 tensioner is about $10-ish, balancer sleeve is $4 & gasket set is about $20. No labor is extensive BUT simple. You need a balancer remover for this project & they can be rented or borrowed.

Your Chilton's is wrong. 90-92 Camaros got a 3.1 engine, and 3.1's never came with MAF sensors. Also, if you ARE going to do a timing chain, and want to give the car a little extra pep...Summit sells a high performance double-roller chain...I believe it's around $95 for the chain and sprockets.

I've heard that a TPS that gets wet will cause a rough idle, but they were talking about the adjustable TPS's on V8's. (Yours has a non-adjustable TPS, the computer readjusts it automatically.)

You could have dirty or clogged or leaking or dead injectors. Have you checked fuel pressure yet (to determine a dead pump)? Checking fuel pressure (gauge costs $40, for high-pressure port fuel injection systems) would also show a leaking injector. To find dead or dirty/clogged injectors you'll need to perform an injector balance test, which pulses each injector for a length of time. You watch fuel pressure drop, and the drop should be the same for each injector. A shop could probably do this for you. I bought my fuel injector tester at http://www.sunpro.com 's garage sale link, paid $20 for it, well worth it for a unit that was orignally $90! (Yes guys, they still have some left!)

If the oxy sensor was just replaced and you're getting code 45, check the wire coming from the oxy sensor to make sure it hasn't melted onto the exhaust pipe. That would cause a short to ground, causing the computer to throw code 45. I routed my wire poorly once, causing the oxy sensor's connector to melt to the exhaust. Had to change the connector on the car-end of the oxy sensor wiring harness!

You say you've gotten a few codes, including code 42. The car can run without EST, but it'll run poorly. Karl might've hit it with a problem with the ignition module. But code 44 (lean) doesn't fit, which is why I'm thinking it's a fuel problem. I'd say to clear the codes out and then go for a drive, and as soon as that SES light pops on, pull over, turn the car off, and check the code. Lets not have multiple codes to work with, that could be hell.

(Yours has a non-adjustable TPS, the computer readjusts it automatically.)
Tom, out V-6 set up is non-adjustable?

I've never touched mine for any reason as I was afraid I would upset/disturb the proper setting.

One less thing/item to reset is just fine for me so I could close hood earlier!

Non-adjustable is right...you can mess with that sucker all you want. No having to set it. I replaced mine in like 2 mins..just took a few screws out, yank, bam, screw, screw, done...oh so easy. Can't beat the TPS..probably THE easiest sensor on the car to change out.

Nixon, only the later V6's got the non-adjustable TPS. Early ones like Karl's '85 are adjustable. BTW, I hate re-setting adjustable TPS's and it can be a pain without a scan tool.

Hmm..didn't know that! Yet ANOTHER thing I love about owning a 90-92...

Yeah, we (Karl & I) have the adjustable TPS sensor. Should be 0.55 volts at idle, +/- 0.05 volts.

hey man.......I have been trouble shooting a hard start on my 3.1

what I read may help. If you have a rough idle, then disconnect the map sensor connector over on the fire wall by the heater core and air conditioner stuff. the ECM will set a default and that should smooth it out if that is it. also there will be a vacuum line that goes to the bottom of it.

does it happen cold or hot?

Capt.

It does it both hot and cold. Checked the coil and it seems to be fine. My friend is calling one of his contacts to see how much he will charge to clean the fuel Injectors

capt shade tree....are you saying it will smooth it out if the MAP sensor is bad?