ChristopherWelkin

Hey fellas. About a week ago my car ('97 3.8 Firebird) has been idling pretty rough. It would start up no problem, but as soon as it starts, the car revs up to 3000 rpm, then settle at about 1200 rpm. It stays at 1200 for maybe about 10 seconds, then the engine revs constantly between 2500 and 700 for about 30 seconds, then goes back to 1200 rpm, where it stays.

I had the SES code scanned, and it brought up 3 codes: p0171, p0174, and p0300. I assume that the first two codes (left and right lean) are from having a cold air intake and are unrelated right? Well the third code is a random cylinder misfire code. Where should I start to diagnose this? Spark plugs? Wires? When I put in the CAI about 3 weeks ago, I checked and double checked for vacuum leaks, so I don't think it's that.


I'm a novice to cars, so I'd appreciate any feedback you guys can offer. Thanks!


**UPDATE ON POST #7**

**UPDATE 2 ON POST #17** 1/27

**UPDATE 3 ON POST #23** 2/5/14. Hopefully this is the last one, getting real tired of this ****

ChristopherWelkin

Bump. No one has anything?

z28SSilvest

Check your MAF connection and also your IAT (little plug on the intake). I don't get how people can screw installing a lid up, but i am 99.9% sure it isn't your spark plugs because it would just be misfiring.

LS6427

iTrader: (2)

Well, all by itself, the only way an engine can rev higher, the ONLY way, is if more air is allowed into the intake. Nothing else that malfunctions can cause an increase in rpm. So it's your IAC valve opening and closing causing the rise and drop in rpm. Lots of things talk to the PCM that can cause it to tell the IAC to open and close. And if the IAC opens and closes improperly, that will cause lean readings because the IAC is behind the MAF and its unmetered air getting into the intake.

I would first try to clean the MAF very good. The MAF is what runs the engine at cold start up, the 02 sensors dont come online until the engine reaches a certain temp, I think 122*F. Use half a can of MAF cleaner spraying (not touching) the entire front side of all the little sensor wires and spray the entire front MAF screen, then hit the back real good too. Then spray the IAT valve thats mounted in the lid to clean that while you're at it.

If the engine runs fine after its warmed up.......it's probably just a dirty MAF. If that's not it, then start chasing other items.

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ChristopherWelkin

z28SS and LS6427, you guys are absolute lifesavers


The MAF and screen didn't look too bad, but I cleaned it anyway for safe measure. When I checked the IAC, it had a bunch of grey crust around the tip and spring. I cleaned the valve and sprayed cleaner and cleaned inside the housing; the idle is waaaay better and runs smoother now.

z28SSilvest

ChristopherWelkin

Okay, quick update. The car ran fairly well after cleaning the IAC valve, but occasionally would still idle rough, so I figured that I had to change it soon.

About 3 days ago, I had to fix the power window wiring on the driver's side. I disconnected the battery before messing with anything. When I got done with everything, I reconnected the battery and started up the car. It idled even worse than before I cleaned the IAC, as the engine actually stalled and died after struggling for a couple of seconds.

The next day, I bought and installed the new IAC valve, and to my dismay, nothing changed. As I wild guess, I thought maybe the PCM was the culprit here with the IAC being new and all, so I disconnected the battery again, pulled the PCM fuses, and let it sit for a couple of hours. I even measured the distance of the IAC's spindle since maybe it was out too far. I turned on the car again: same thing. It would immediately idle rough for maybe 20 seconds, then just give up and die. I tried lightly stepping on the gas, but it was totally non-responsive.

Any suggestions what it could be this time around?

z28SSilvest

Either the PCM or my other guess would be possibly a coil pack

ChristopherWelkin

Are there any tests to check either one for faults?

z28SSilvest

I mean.. You could check your fuel pressure, oil pressure, and if you feel up to it, do a compression test to see if the block is even in good shape.

LS6427

iTrader: (2)

You tapped the throttle while it was running and you got no response? Possibly a worn spot in the TPS, which will give the PCM wrong info and cause all kinds of weird idling problems.

Are you getting an SES light? Even it comes on and goes off.....check to see what codes might be in there.

Random misfire codes and rough running with stalling out can also be a failing Coolant Temp Sensor. The 1998 LS1 PCM's like mine will not run with a bad or failing Coolant Temp sensor. Maybe the 97 3.8 is the same. And NO.....you will not necessarily get a code. Mine didn't throw a code or an SES light when it was failing.....but I had horrible misfiring, backfiring and the engine would stall if I touched the gas during cold start up. Basically, cannot drive the car with a bad temp sensor.
I know later years don't have that issue.

Again....buy one and see if it works. If not, return it for a refund. Just tell me you never installed it because its the wrong type and you already found the right part and put it in.


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ChristopherWelkin

I probably will end up doing all those now that the car's not running.

When the car was idling really bad the first time around, the SES light was blinking on and off until I shut off the engine. The second time around, when it actually stalled, the light didn't come on at all.

I'll check into the coolant temp sensor if that may be the culprit too. Is it a pain in the *** to replace on your LS1?




Thanks again for all the help you guys. This car is my DD so I'll have to really be patient and get this car running ASAP. For the meantime, it's back to the city bus to school and work

LS6427

iTrader: (2)

On an LS1 it takes maybe 3 minutes to replace it with a crescent wrench. Not sure where it is on a 3.8. I assume its also in one of the heads.......

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Undertow74

iTrader: (45)

Check your 02 sensors bet they are the culprit especially with those codes. when were the last time they were replaced

ChristopherWelkin

Not since I bought the car, which was about 6 months ago. Lord knows if the previous owner changed it or not, so it might be a good idea to check it out. Are O2 sensors like the MAF where I can unplug them then start the car to see if it changes anything?

LS6427

iTrader: (2)

If both sides are showing a Lean code, that means BOTH sensors, which are totally independent of each other went bad at the exact same time. Highly unlikely. But anything is possible with these cars......lol

The 02 sensors don't start talking to the PCM with infomration till the engine gets warmed up.....that magic 122*F or higher. So I guess in theory if its running/idling like crap and you unplug them and nothing changes.....maybe it can be two sensors are going bad. Because if you unplug a good 02 sensor while the engine is hot and running....it will all of a sudden get very rich....and start to misfire, hesitate and lose power. You will smell raw fuel coming out the tailpipes.

You never mentioned smelling fuel......and that's what happens when 02 sensors go bad......it runs very rich. You can smell it easily and your gas mileage gets cut in half. Plus the engine will have no power while cruising around and it will be stumbling and misfiring the while time.

Bad 02 sensors also don't cause the rpm's to go up and down like that.......bad 02 sensors just means an terrible running engine that seems like its about to fall apart........

.

ChristopherWelkin

Okay, so something really weird happened today, I hope one of you guys can figure out what this means. After getting home from work, I had an hour before sunset to mess around with the car a bit, so I decided to re-check the sensors on the throttle body. I had taken out my cold air intake yesterday, so the very first thing I did was put it back on, but I didn't connect the IAT sensor. I also had the MAF unplugged. I turned the car on, and it idled perfectly for about 20 seconds, loped mildly (not as bad as it had been) for another 20 seconds, then evened out again.

I turned the engine off, plugged both connectors, turned it on, and it idled like **** once again. So I tried unplugging both, unplugging just the MAF, then unplugging just the IAT sensor (I even tried putting in a new TPS I had lying around for ***** and gigs), but alas we were back to square one.

Is this significant at all? Or was it just a coincidence that the engine ran fine for a little bit?

ChristopherWelkin

ttt

Does anyone know how to post a video on here from an iphone? I'll try and take a couple of videos, maybe that might help.

I feel like whatever my car's problem is, it can't be mechanical since it ran well even for a little bit. So it must be something with a sensor or electrical, right?

ghardester

Have you re-checked the codes lately? Are you still getting a random misfire code or has it pointed to a cylinder yet?

The reason I ask, may not be related to your problem, is that I had 2 3800 V-6s (including a '97) and the spark plug wires were prone to going bad because they reach over the top of the engine. One time a wire went bad and I replaced them but I still had a mystery, intermittent problem.

It turned out that a bad wire had caused one of the 3 coils to blow. If you think you can identify a particular cylinder as misfiring you can move one of the coils on the coil pack to a different location and see if the problem moves.

Before going further I would recommend taking each plug wire off, one at a time of course, and inspecting it. If you find a worn spot underneath you probably have a bad wire. If so, and a new wire doesn't fix it, you may have blown one of the 3 coils.

Just some food for thought. Great engines, I only ever had problems with the wires and coils.

ghardester

Sorry I didn't see this and include it in my last post. The SES light blinking is a multiple misfire indicator. Most of the other possible problems mentioned are not going to cause this.

Before you get too worried about other problems, be sure of your plugs and wires. Simplest things first.

Occam's Razor and all that. (Look it up).