: Check Engine Codes, vibration



MN-STS-LOVER
07-18-07, 04:56 PM
Hello,
First let me say that I'm new to this forum. Heard about it from a friend in FL that owns a CTS. Love the site. I bought a '98 STS in December. I love the car! What a ride! I have had to do some work on it...but that is to be expected. I came in with eyes wide open. I have 2 issues. I continue to get 2 codes: P0171,P0174 (bank 1 & bank 2 running lean) I do have a code reader and can erase the codes. The engine runs great and I see no problems related to the codes. The codes only come back if the car is idling for a period of time (5+minutes) never while driving? anyone know what the codes mean? could it be as simple as a fuel injection cleaning? Issue #2: the car was a 1 owner with only 76,000 on it when I bought it. The previous owners were an older couple that drove it from MN to AZ and back every winter. While accelerating through 2,000 to 2,400 RPM I get a vibration through the gas pedal (this is the range of 70-75 mph) could the fact that the previous owners made long trips at sustained speeds have caused a "memory" in the balance of the engine and that is what I am feeling?

Ranger
07-19-07, 01:58 AM
1. Check for a vacuum leak on the manifold or the rubber coupler between the TB and the manifold.

2. No. A vibration at those speeds is somewhat common and usually tire related. Get a road force balance.

Submariner409
07-19-07, 11:07 AM
Guessing that the car now has 82,000 on it, there's also the chance that the Bank 1 and 2 O2 sensors, and maybe the after-cat sensor, are on their last legs. Go through the tech archives and search function at the top of the page and look for DIC, codes, etc. IF you continue to get O2 sensor-related codes, but the car runs normally otherwise, with 16-19 mpg in town and 23-27 mpg on the highway, colorless exhaust pipes, good acceleration, then suspect the sensors themselves. The vibration seems to be fairly common in this car series. A good tire rotation, balance, wheel and hub flange cleaning, and torque nuts to 100 ft/lb. should get rid of most if not all of it.

AJxtcman
07-19-07, 07:53 PM
1. Check for a vacuum leak on the manifold or the rubber coupler between the TB and the manifold.

2. No. A vibration at those speeds is somewhat common and usually tire related. Get a road force balance.

This car has no Plenum (coupler).
.
.
Take a long hard look at the rear of the intake. It is at the other front of the engine. I am talking about right behind the Power Steering pump. You will find a flapper valve used for backfire releaf. Look at the valve and study it. It is hard to see. You need to look for a rubber seal on the flapper part of the valve. It is orange. The seal falls off or partialy falls off and causes both banks lean.

Ranger
07-19-07, 09:13 PM
This car has no Plenum (coupler).
It doesn't? :confused: Which ones do?

MN-STS-LOVER
07-20-07, 02:40 PM
Thanks for all the input. As for the vibration, It is not speed related, rather RPM related. It happens at all speeds in all gears as the RPM's pass through that range. There is no vibration in the chasis or steering wheel, just the gas peddal. Makes me think of a harmonic imbalance somewhere in the engine, that is why I mentioned "memory". As for the check codes: I will look at vacuum and the backfire relief valve. Right after I bought it, I had to have the intake manifold replaced. The housing for the back-fire relief valve was cracked. Maybe the dealer missed something while installing the new manifold. The code problem did start happening shortly after the work was done.

Thanks again for the input!

AJxtcman
07-20-07, 03:14 PM
It doesn't? :confused: Which ones do?

00 on up. The 95 to 99 T-bodies bolt to the spacer that t he EGR tube attaches to.

AJxtcman
07-20-07, 03:18 PM
Thanks for all the input. As for the vibration, It is not speed related, rather RPM related. It happens at all speeds in all gears as the RPM's pass through that range. There is no vibration in the chasis or steering wheel, just the gas peddal. Makes me think of a harmonic imbalance somewhere in the engine, that is why I mentioned "memory". As for the check codes: I will look at vacuum and the backfire relief valve. Right after I bought it, I had to have the intake manifold replaced. The housing for the back-fire relief valve was cracked. Maybe the dealer missed something while installing the new manifold. The code problem did start happening shortly after the work was done.

Thanks again for the input!

I replaced an intake with a new one once. I had to switch the valve over. Most of the 99 and prior cars are out of warranty, so we get used intakes. We have a hard time getting good ones.