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2002 DTS rough idle when engine warmed up

Started by TonyZappone #2624, August 24, 2016, 08:57:06 AM

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TonyZappone #2624

In the past month, I have replaced the spark plugs in my 2002 DTS, and also replaced the torque converter and torque converter solenoid.  (Total around $2500). The car has ca. 106,000 miles, and looks and runs like new.  (except for the rough idle when warm).  Expecting the worse, I looked in the cooling reservoir and found cooling levels where they should be when cold).  If in fact the proper cooling level dismisses the possibility of blown head gaskets, can anyone guess what the problem might be?  I put a large dose of Seafoam in the gas, but after 20 miles of hard driving, this didn't seem to cure anything either.  Any ideas?
Tony Zappone, #2624
1936 Pierce-Arrow conv sed
1947 Cadillac Conv cpe
1958 Cadillac conv
2016 Cadillac CT6 Platinum
2022 Chrysler Pacifica Pinnacle

TJ Hopland

I assume you are not getting any codes?   Do you know if this is return less or is there a fuel pressure regulator?  If its got a regulator that is a common place for a problem that won't trip a code. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Dan LeBlanc

My '04 was the same way.  Ended up being a bad coil on plug.  Would only trip the service engine light when under WOT.  Spark plugs were changed first - even though they were still ok and had some life left in them.  This was at 62k miles.

Unfortunately, could only buy the coil cassette which is for an entire bank of cylinders and that set me back nearly $400
Dan LeBlanc
1977 Lincoln Continental Town Car

TonyZappone #2624

Mine does not trigger the check engine light.  Maybe I should just drive it and not worry about it?  To check those coils do they have to go through the same labor intensive process as it was to change the plugs?
Tony Zappone, #2624
1936 Pierce-Arrow conv sed
1947 Cadillac Conv cpe
1958 Cadillac conv
2016 Cadillac CT6 Platinum
2022 Chrysler Pacifica Pinnacle

Dan LeBlanc

The dealer can put it on the Tech II scanner and identify which cylinders.
Dan LeBlanc
1977 Lincoln Continental Town Car

TJ Hopland

If its not setting a code its probably not related to a single cylinder so that kinda points away from a coil or injector problem unless its just not bad enough yet.   If you got a light and a missfire code then you would swap coils around and injectors to see what moves the problem.   With no light I would be looking other places first.   Like Dan said its possible a dealer type with the proper equipment could detect a single cylinder misfire that the onboard stuff can't. 

I looked at a parts list and there is a fuel pressure regulator listed for that car.   I have no idea where it is but it looks like a typical regulator that would have a vacuum hose on it.   IF you can find it and pull the vacuum hose off check the hose for any signs of gas.  If there is any sign of gas there the regulator is shot.   A bad regulator gives you some fuel leaking direct into the intake and tends to run the pressure higher.  For the most part the system can compensate but idle is tricky so that is often a place where it shows up.   I have never seen a bad regulator trip a light.   Longer than usual cranking is also a sign of a regulator issue. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Dan LeBlanc

I only had the SES light under WOT conditions.  Not under normal cruising.
Dan LeBlanc
1977 Lincoln Continental Town Car

76eldo

If it acts up long enough it will throw a code.
The O2 sensor will pick up an imbalance between bank 1 and bank 2.

Could be a bad injector or two.

Everything starts going at 100,000 miles on these cars including injectors.
Plugs, wires, coil packs, etc.

Brian
Brian Rachlin
Huntingdon Valley, Pa
I prefer email's not PM's rachlin@comcast.net

1960 62 Series Conv with Factory Tri Power
1970 DeVille Conv
1970 Eldo
1970 Caribu (?) "The Cadmino"
1973 Eldorado Conv Pace Car
1976 Eldorado Conv
1980 Eldorado H & E Conv
1993 Allante with Hardtop (X2)
2008 DTS
2012 CTS Coupe
2017 XT
1956 Thunderbird
1966 Olds Toronado

brian faull clc#25881

Tony, a few things to check. Is your throttle body dirty? go under the hood and manually open the throttle and let it snap closed then very slowly try to open it again. If it feels sticky at all when first opening you should clean your throttle body. Have you ever had a top engine cleaning service performed on your car. The Northstars get very carboned up, especially if they are driven around slowly at low rpm. These engines love to get revved up high. It helps keep everything cleaned out. They all need a top engine clean occasionally. Check your fuel pressure regulator like someone else suggested. Pull the small vacuum hose from the regulator and if any fuel is present replace it. This usually causes a hard start condition though. Also when was the last time your fuel filter was changed. I recommend doing it every 30 - 40 k miles. They will run with a clogged filter for a long time and usually burn the pump out before they quit running. And last but not least, most commonly the boot between the plenum and the throttle body tends to crack and cause a vacuum leak which will sometimes affect idle and not throw a code. The easiest way to check this is pull the engine cover and give it thorough look over. If you do not see anything spray a little carb cleaner around the boot and listen for an idle surge. In addition to this verify that all the hose clamps from the air filter to the throttle body are tight and the hose is properly seated. I have seen that happen several times. Someone has the air filter changed and one of the hoses is not tight and you get an idle stumble. If you need any further help, feel free to give me a call. Thanks, Brian. 412 952 6027. 
brian faull clc#25881

TonyZappone #2624

Brian:  Thank you for the most comprehensive report.  I will have all these things checked. 
Tony Zappone, #2624
1936 Pierce-Arrow conv sed
1947 Cadillac Conv cpe
1958 Cadillac conv
2016 Cadillac CT6 Platinum
2022 Chrysler Pacifica Pinnacle

john estes

I have seen a head gasket leaking into cylinder on cool down. This was causing the spark plug to foul with coolant and after a minute or so of run time the plug will dry and misfire will be gone. If you know which cylinder is misfiring you could remove that spark plug after a hot soak and see if there is signs of coolant. The misfire can be so quick to go away that a dtc will not set but the misfire will show on the scan tool misfire graph.
John Estes