s7ven

So...I just officially joined the ranks of the proud LS1 owners with a 2001 Pontiac Trans Am. I've dreamed of owning this car since I was about 16 years old. I just flew about 600 miles and then spent the next 10 hours driving it back home.

Anyway, to the topic at hand, on the way back a check engine light came on with codes P0171 and P0174 (Lean). In addition to that, the car seems to be proned to slight back firing(nothing severe, just light popping and cracking) when down shifting or down rev at idle. The car has no problems running or starting but the idle is what I would consider "rough".

Any idea where I should start troubleshooting? I thought about taking a look at the MAF and IAT sensors and seeing if they were dirty but just haven't had the chance. Other than that, vacuum leaks seem to be pretty common problem but I don't have a smoke machine, is carb cleaner a viable choice?

Don't know a lot about the car but I know nearly everything is stock except for the SLP intake and Flowmaster catback.

RPM WS6

iTrader: (3)

Welcome to the site and the LS1 owner's club.

I would start by cleaning the MAF. This is the source of many driveability issues, and is such a simple thing to do. If the car has had a K&N style filter for any period of time, then it makes cleaning the MAF even more important (oil residue builds up on the wires over time).

Vacuum leak is another good possibility for your issues. I would start by inspecting the PCV system. This is often the source of vacuum leaks on these cars as they age. The entire PCV line is known for cracks/breaks, but I would start by checking the valve boot and the elbow where it attaches to the intake. This is where mine started to come apart.

Good luck.

s7ven

Thanks, I'll try cleaning the MAF sensor tommorrow and see if that helps. I'll also take a look at the PCV line while I'm at it.

jimmyblue

iTrader: (11)

I think I'd start with the O2 sensors. The lean codes
are about trimming it into the weeds, and most air
metering faults won't push you that far unless they
are really gross. A fouled-out pair of O2 sensors will
take you there, easy. Sometimes people will kill the
codes for those, and let it ride until something else
(like this) goes wrong.

PCV boot at the TB often tears, that's a vacuum
leak to look for if your idle is high.

s7ven

So I cleaned the MAF/IAT, took out the light with my scanner and no return of the light yet but I've only driven it about 20 miles. Also, put in some good gas and Lucas fuel treatment for good measure. As far as I can tell the PCV line looks like its in good condition, no cracks and it fits pretty snug.

Still backfiring slightly, idle has improved slightly but still a little rough.

Not sure how to check the O2 sensors...can I do that with my scanner? Here is a live feed of my scanner readings at idle(warmed up):

O2S11 -> 0-6%
O2S21 -> 0-4%
MAF -> .66 lb/min
Ign Adv -> 19 - 20 degrees
IAT -> 120 degrees F (51 degrees F in my garage)
MAP -> 8.8 in hg.
RPM -> 790
LT FTRM2 -> 18.7 - 21%
ST FTRM2 -> 0-3%
LT FTRM1 -> 19 - 21%
ST FTRM1 -> -1.5% - 0%
Coolant Temp -> 194 degrees F

I have a few more readings for O2 voltages but didn't bother posting them.

s7ven

Okay so the codes are back now, I reset the computer via disconnecting the battery for a minute or so and then started her up. Within a few minutes 2 counts of 171 and 174 codes came up.

Not sure where to look next, only other clues I can provide is that there is what sounds like a hissing or the sound of electrical discharge under the car that comes and goes as the car idles (exhaust leak?). Also, the engine does make a audible knock which I believe to be coming from the top part of the engine, it's high pitched in nature. The noise accelerates with the speed of the engine....It's barely noticable and not always there.

The oil pressure seems to be a little high, around 70 under high load and 60-65 at idle (I'm using the dash gauge). I've got a new fliter and some oil for an oil change so I'm going to see if that helps.

RPM WS6

iTrader: (3)

Why are the O2 values stated in a percentage? The readings in millivolts would be more useful, if your scanner supports that.

LT fuel trims are too high (explaining the lean codes) but are mostly equal so if it's a vacuum leak than I would suspect it to be macro and not bank specific (such as an intake port leak). The PCV line goes all the way around the back of the intake to meet up with the other side of the engine, so it's possibile there could be a break somewhere that you can't see. You could try pulling the line off at the intake or valve and see if the idle is effected by doing so. If not, then something is up with the line somewhere.

I'm assuming the car is an M6 based on the idle speed you posted. If so, the "knock" from the top part of the engine might be due to bent push rods from a missed shift or mechanical overrev at some point. This would also be consistant with the idle issues and such. Or the noise might just be the usual piston slap or even a lifter issue.

60+psi of oil pressure at idle is pretty high for a stock pump. Sending unit might be giving a bad reading, or the oil might be very thick. Probably a good idea to change it if you don't know what's in there. Be sure to check the magnet on the drain plug and also pay close attention to what pours out of the engine on this first change (some fine mesh like a window screen would work well to catch any debris).

s7ven

I changed the oil, probably the easiest car I've changed oil on besides the filter being a bitch to get off. (bloody knuckles) Put in the whole jug of mobil 1 10W-30 and a mobil 1 filter. I did notice 1 or 2 flakes of metal stuck to the magnet on the oil plug but is that bad? I had forgotten about getting a screen for the oil so I can't really say for sure if there were any metal particles there. Oil pressure is still running about 60 at a warm idle but haven't really drove it anywhere yet. I don't trust the dash gauge too much though.

I pulled off the PCV line while it was running, it almost killed the car and the idle was way rougher than it was previously.

Yes the car is a 6 speed, I made a recording of the noise and I attached it, it's pretty low quality so I don't think you will be able to tell much. You can definitely hear the sound I was talking about though, almost a kind of squeaking sound.

I'm going to try and get the car to my mechanic at the end of this week...I'd like to be able to fix this myself but doesn't look very likely at this point.

s7ven

Well the idle seems to be getting worse and now I'm even getting some white smoke on startup and at stops....I remember my old 3.7L V6 99' Firebird had some small smoking at first that turned into a huge cloud of smoke within a few months...that turned out to be a head gasket leak.

I'm getting the car to my mechanic on Sunday and he's going to work on it early next week. If it turns out to be a bad head gasket, would I be better off getting it fixed or just getting a new motor? I know my last head gasket cost me around $1200 but that included some valve machining/fuel regulator replacement. Not too mention the knocking is not getting any better, cars still got tons of power though....so idk...

I just got my annual bonus from work for $6000 plus I've got another $3000 saved up...I'm sure $9000 would get me a pretty sweet setup but I prefer to spend < $5000 if possible. I can't really do any of the labor myself since I lack any decent tools/knowledge but I would love too if I could....

Pending the response from my mechanic, what would you guys suggest?

lt1pwr1

iTrader: (1)

As RPM mentioned, you most likely have a vacuum leak. These cars are very well known for going through intake gaskets. You can spray some carb cleaner around the intake and see if your idle changes. My bet is on that since it seems to be affecting both banks.

Also, when you drained the oil did it look dark or was it milky? Milky=coolant in the oil. However, I HIGHLY doubt you have bad head gaskets as that is pretty rare on these cars unless it was overheated for another reason.

s7ven

By milky, do you mean light colored? To me the oil looked pretty normal. Also, the coolant level is not dropping, still full.

s7ven

Mechanic ran a smoke machine on the intake, the gasket needs to be replaced and so does the PCV line. Going to run me about $300, do you think I'll gain some more power after getting rid of the leaks?

Mista Blazer

iTrader: (4)

I currently have a bad PCV line in the back, from vlave to T- Fitting. My fuel trim was maxed out at idle my ridding looked just like yours when my tuner hooked up, my maf would read about 2000mv with the vaccume like plugged and my trims went down to about 10% id look at the whole PCV line. The way ours are ran they are exposed to the heat and from what i have been told the oil eats at the lines. i dont think a bad gasket could cause this big of an issue. you can do all of this yourself if you want to save a few bucks, i plan on looking up the hose size for the PCV and building my own. Friends Discount at GM is 95.00 just for the setup.

s7ven

Unfortunately I already pulled the trigger on getting the work done but yea he told me the PCV line by itself was going to run around $100 which is ridiculous for a rubber hose with a spring valve in the middle...

If I ever run into PCV line problems again I will definitely be making my own.

TransAmBlue

Before you do anything have the fuel filter changed and check the fuel pressure with the car running.

s7ven

All seems to be well now, when I picked up the car, the fuel trim was down below 10% on both banks and I would imagine it's going to keep getting lower as it re-learns. Hole in the PCV line about as wide as your thumb where a grounding strap was attached. The knocking that was there before is no longer there and exhaust crackle/backfire is considerably better.

It runs and drives like a different car now but I have one more question that is not that big of a deal but I'm pretty picky. Got a squeaky belt it sounds like, not audible at idle but as the RPMS increase it's frequency/loudness increases as well. The serpentine belt looks relatively new...

Any ideas?

RPM WS6

iTrader: (3)

Glad you got the initial issue sorted out now.

As for the belt squeak, this is a common problem as these cars age. If the belt has been ruled out, then the most likely culprits will be a tensioner pulley or an idler pulley (there are two of each between the A/C belt and the main belt). You can remove the A/C belt (you'll have to take the main belt off first) and drive the car with only the main belt re-attached, then you'll know which belt system is causing the noise.

You can sometimes tell which pulley is bad by spinning the pullies by hand while listening for any noises and checking for any wobble or excessive free spinning, any of which would indicate a bearing issue. Sometimes there are no apparent signs though. Any accessory pulley can be the source of noise, but the idler and tensioner pullies are most common.

s7ven

So I'm bringing this thread back from the dead, today the SES light came back on with the same codes as before. Long term fuel trim is running as high as 24-25 now at idle. I'm going to check all the hoses and stuff again to see if there is a leak...

garygnu

how many miles on the car ?what dose it idle at now ?

s7ven

70,000 miles on the car, it idles at around 800RPM