: 01 DTS running lean codes 0171, 0174 what to look for?

06-03-10, 05:39 PM
I have a 01 DTS that is idling rough and is giving codes PCM 0171 and 0174. I have checked the obvious and no visible vacuum leaks or dirty filters. I have had mice in the engine bay though.

The idle shows a constant 650 rpm at a stop or in neutral but you can hear it wondering around funny. It was to the point of almost dropping too low to run.

Would a faulty fuel regulator or fuel pump cause this? What about the EGR?

I checked the PCV and it has vacum and rattles around but it is coated in a bit of oil

06-03-10, 05:59 PM
Have you removed the engine cover, started the engine, and squirted a shot of carb cleaner or starter fluid down at the screw clamp for the plenum connector between the intake manifold and throttlebody ?? Listen for an idle speed change.

#2 in the diagram. Very common vacuum leak, (and that is a code-setter for your 2 codes) in a 2000+ Northstar. $40 at a dealer only.

Look in General Cadillac Discussion, Tech Tips, for how to do the job; "Plenum Replacement, 2000+ Northstar" or close - first page.

06-03-10, 06:29 PM
Interesting you point there, that is what Chiltons is also saying and I had recently had the starter replaced so they were most likely rough on that part.

06-06-10, 03:00 PM
Sure enough the problem was a blown plenum. It took around 1.5 hours to replace and runs like a champ.

Know on to see if all that oil that has collected in my manifold is bad.

06-06-10, 03:27 PM
It took 9 years for the cam covers to weep enough oil to get into the valley. Don't sweat it. (Wait 'till you decide to change the ACDelco #41-987 Platinum plugs...........those wells are sealed with O-rings which also weep :sneaky: )

If the intake manifold itself has quite a bit of oil goop in it you can clean it in a parts wash tub BUT make very, very, very sure that it's completely dry inside with no flakes or loose crap - why blow a cylinder - otherwise leave it alone. Cleaning that manifold is practically impossible as you can see from trying to find out what's inside.

06-07-10, 11:55 PM
The oil that collects in the manifold is normal. It is a product of the PCV valve. Crankcase gases are fed into the manifold to be burned. When you shut down, they condense and fall out in the manifold and collect over years and years of use. Perfectly normal and harmless.