01 Dts Rough Idle

pontiacsouth · #1 (**permalink**) 03-10-08, 09:09 AM

My DTS has started to have a rough idle last week. Feels like it has a beefy cam in it when its idling since it sort of rocks the car. I can also feel it chugging a little under acceleration. What would be the cause of this? I have some plugs i am going to throw in this weekend, since i dont know if the previous owner ever changed them. The mileage is 128k. Is there anything else i can replace to get my smooth idle again? let me know what u think. thanks

submariner409 · #2 (**permalink**) 03-10-08, 09:26 AM

What kind of plugs are "some plugs"? Northstars like ACDelco, period, and I believe your engine takes #41-987, $4.90 in packs of 8 from www.rockauto.com. You'll probably find a couple of tracked or torn coil connector boots, so replace them also. (The Packard/Delphi p/n.) Make sure the ground spring in the coil cassettes is "springy". Removing the A.I.R. valve on the back cassette can be a bit hairy.

pontiacsouth · #3 (**permalink**) 03-10-08, 09:41 AM

submariner409, i got delcos as i read the previous posts bashing all others. I am dreading doing the back plugs, will have to stock up on beer before tackling them. I will try to find a good set of boots also.

thanks for the reply...

submariner409 · #4 (**permalink**) 03-10-08, 10:06 AM

The boot number, GM, is 12163650, $2.85 ea. at Rockauto, but a non-stock item. Try Gmotors in Gainesville (Brasington Cadillac), GMPartsDirect, or Flow Chevrolet/GM in Raleigh (?) NC.

VIPERRACING · #5 (**permalink**) 03-10-08, 08:57 PM

Quote:

Originally Posted by pontiacsouth

My DTS has started to have a rough idle last week. Feels like it has a beefy cam in it when its idling since it sort of rocks the car. I can also feel it chugging a little under acceleration. What would be the cause of this? I have some plugs i am going to throw in this weekend, since i dont know if the previous owner ever changed them. The mileage is 128k. Is there anything else i can replace to get my smooth idle again? let me know what u think. thanks

Im having the same problem with my 99 sts with only 80,000 miles. Would the egr valve cause this problem also? How about bad intake gaskets? Thanks.

**Ranger** · #6 (**permalink**) 03-10-08, 09:32 PM

Bad intake gasket would likely cause a high idle and a P0171 or P0174 code. EGR sounds more likely, but it should set a code as well. Have you cleaned the TB?

VIPERRACING · #7 (**permalink**) 03-10-08, 09:37 PM

No codes and I have cleaned the throttle body and also have seafoamed the intake. Im thinking of putting a egr block off plate to see if that helps out. Are the same ranger that has the z06 ? Thanks for any help.

**Ranger** · #8 (**permalink**) 03-10-08, 09:41 PM

Quote:

Are the same ranger that has the z06 ?

Nope, he's an impostor.

pontiacsouth · #9 (**permalink**) 03-12-08, 12:11 PM

after checking the onbord codes i have a P0300, which is misfire detected...

pontiacsouth · #10 (**permalink**) 03-17-08, 07:38 AM

i changed the plugs & boots this weekend. there is still a misfire code coming up. although the engine does seem to run smoother. i did clear the codes b.t.w.

i looked inside the throttle body. it was pretty black in there. i cleaned the butterfly off but how can i clean out the intake. i heard of seafoaming but how can i do it???

maybe one of the coils are bad or its just a dirty intake??

submariner409 · #11 (**permalink**) 03-17-08, 12:28 PM

Do not remove and block the EGR system. The ignition will sense the resulting low speed/part throttle knock and default to limp-home retard timing, as well as set airflow and mixture codes.

Did you remove and clean/replace the plug connector boots? They sometimes carbon track and cause a misfire. How about the spring tension on the coil cassette ground springs ?

DO NOT shoot the intake full of magic potions. There's a thread here from last fall about someone who did just that and had a devil of a time stopping the smoke and banging that resulted.

Look for several threads here, and in Seville/Deville over the last 8 months, concerning intakes, throttlebodies, rubber plenums, and cleaning. (There's another, similar, thread right next to this one........)

I'll bet the misfire comes from either intake manifold gaskets, bolts, or a torn plenum.......has an oxygen sensor lean code (P017x) set ?

**Ranger** · #12 (**permalink**) 03-17-08, 02:17 PM

Just clean the TB bore, Throttle plate (backside & perimeter). Like Sub said, forget the manifold. That is normal crankcase gases and EGR gases that settle out when the engine is shut down. It does no harm and will only return in short order.

pontiacsouth · #13 (**permalink**) 03-17-08, 05:21 PM

has an oxygen sensor lean code (P017x) set ?

no, there are no other codes the the generic P0300 misfire.

i have different coils to put on someday also. a lot of people said that this have cured their missfires.

i'll just leave the intake dirty, just saw it was all carbon build up in there and thought i gotta clean it out.

thanks for your advise

**Ranger** · #14 (**permalink**) 03-17-08, 10:59 PM

A lean O2 sensor would point to a vacuum leak.