: 2002 Eldorado rough idle

04-21-10, 11:54 PM
Can someone offer some easy checks I can do myself before I start spending money at the local Cadillac dealership? About two weeks ago I started to notice a rougher idle. Then I got a check engine light but all of the codes were history, no current. I got some advice then cleaned the MASS sensor with MASS cleaner. No difference. Several days later the check engine light went off. :bouncy: However, it still idles rough. Is it possible to disconnect, reconnect sensors and locate the problem?

04-22-10, 08:29 AM
Remove the engine cover and check both sides of the PCV tubing for a vacuum leak - you have a fixed orifice, not a rattle valve. Check the several vacuum lines which originate at the throttlebody as well as the EVAP purge solenoid and tubing which is attached to the rear side of the throttlebody. With the engine running at idle pull the vacuum line off the FPR nipple - right rear fuel rail - and check for raw gas in the nipple or line. Any gas and it's FPR replacement time. Use a stethoscope and listen to each fuel injector for a rhythmic "tick-tick-tick-tick" at idle. Any TB cleaner spray left ? Remove the air intake ducting, block open the throttle butterfly and use rags, a toothbrush and cleaner to remove the gunk from the throttlebody bore and butterfly. DO NOT get any liquid cleaner into the intake manifold - if you want, stuff a lint-free rag into the throttlebody, past the butterfly and do the cleaning, then carefully pull the rag with long needlenose pliers. Air filter ?? Spark plugs ?

04-22-10, 10:45 AM
Also spray some of that cleaner near the underside of the plenum (rubber coupler between the TB and the manifold). If the RPM increases, the plenum has a crack in it.

04-22-10, 10:48 AM
Thanks for the advice. I will be checking for vacuum leaks today. I just replaced the air filter with no change. With only 56K, I was waiting on spark plug change. One thing I keep thinking about; this problem started shortly after I used some Lucus brand 'upper cylinder lubricant'. The guy at O'Riely recommended it when I was in there 'browsing'. It was on sale that day. Do you think that had anything to do with it?

04-22-10, 10:52 AM
It shouldn't, but it wouldn't be the first time someone had problems after adding snake oil. Where did you put the stuff? In the tank? If all else fails, then pull the plugs and see if they got fouled.

04-22-10, 02:02 PM
Given the rate at which the average Northstar consumes oil, upper cylinder lubricants are the equivalent of "Bringing the coals to Newcastle" - just plain, flat not needed. Consider that adding extra oil to the gasoline in an engine which uses low-tension piston ring technology is a perfect invitation to ring sticking from excess carbon buildup...................as well as spark plug fouling.

Now, maybe if the car were to be driven across Texas at 135 mph for 7 hours, then maybe - but never for a daily driver, especially a "town car".

04-22-10, 05:11 PM
I may add checking spark plugs to my list to check for fouling. What fuel system cleaner who you recommend? Or does the N* need it?

04-22-10, 05:26 PM
Once every 6 months I dump in a 20 oz. jug of Chevron TECHRON and a fill-up with Shell 93 - before a road trip.

Google "top tier gasoline" to find out why.

04-22-10, 06:07 PM
Hey Sub, check this out. Particularly post #7 & 8.

04-22-10, 09:59 PM
I wish there was top tier gas in my area. All I have near me is Mobil, Noco, Sunoco, Valero, Citgo, and a few others. Which do you guys think carry the best gas?

04-22-10, 10:07 PM
"Best" gas is like "best" oil. Define "best". Pick one. They're all the same.

04-22-10, 10:15 PM
What makes fuel from Shell better than fuel from Sunoco? I just want to use the best possible fuel I have available in my area..

I read that some fuels have lower quality additives than others. Others being top tier gasoline.

04-22-10, 10:51 PM
Who said Shell was "better" than Sonoco, Shell? Of coarse they will and Sonoco will say they are better. Remember, what you are reading is marketing. That's what marketing is. Trying to convince you that their product is better than the competition so you send your money their way. Personally, I have never had an allegiance to any brand (oil or gas). I simply buy from whoever has the best price (for over 40 years) and I have never had a fuel (or oil) related problem. That said, people have their preferences, and like with oil, they will fight to the death that this brand is better than that. I remember when I was in my 20's, my neighbor (same age) thought Shell was "the best" and would use nothing but (probably still does). He didn't know what he didn't know (and probably still doesn't). Bottom line is one does exactly what the other does (gas or oil) and none will do any harm. Pick your favorite (if you want one) for whatever reason and use it.

I read that some fuels have lower quality additives than others. Others being top tier gasoline.
Did you read the link I posted above? JohnnyG's post should pretty much confirm what I have been saying.

04-22-10, 11:52 PM
Ok, I understand and agree that top tier gas is a gimmick, but how about the techron fuel treatment? Waste of money? How about any fuel system cleaner? Are they all gimmicks?..I wouldn't doubt it.

Also, would running 89 octane fuel contribute to a mild rough idle when my car requires 91 octane? I wouldn't think so, but that would be an easy fix since I've ruled out: plugs, wires, air filter, TB, FPR..

04-23-10, 08:17 AM
...........unless Johnny G is simply an anonymous Internet lurker who needs identity and personal reinforcement, and we all know that personal gas wars are as real and avidly fought as "oil wars".

Chevron TECHRON is the gasoline additive which qualifies a top tier fuel.

The "top tier" thing is a real study/recommendation done by several pretty good automotive manufacturers, so it's probably not snake oil or marketing hype - Chevron (the TECHRON additive manufacturer) most likely is not paying the involved car manufacturers and other refiners a kickback, either. Ford's not in the group - they recommend BP - so what's that worth ?

I use a Shell/Citi Master Card which rebates me 5% of all Shell Oil purchases. At our current $2.80 a gallon that's 14 cents a gallon, or a final cost of $2.66 for 87. Shell is never $.14 more than Texaco or BP or Chevron, so the savings is real, and the East Coast is covered with Shell stations. It's a no-brainer.

In a properly functioning engine 87, 89, 91 or 93 octane gasoline will have absolutely no effect on idle quality.

04-23-10, 11:45 AM
Do the fuel system cleaners actually work? Like Techron, or the Lucas Oil stuff..??

What is the actual difference between 87 octane and say 91 or 93 octane?

04-23-10, 12:53 PM
Techron is the ONLY one I'd use. GM recommends it when needed and uses it in the ring cleaning procedure.

The ONLY difference between different octane fuels is it resistance to detonation, nothing more. Don't get caught up in the marketing hype of more power, cleaner burning or smoother running by using higher octane than you need.

Sub, JohhnyG is legit. I've known him there for years.

I use a Shell/Citi Master Card which rebates me 5% of all Shell Oil purchases.
:thumbsup: Reason enough.

04-23-10, 01:11 PM
:D I'll just use 91 octane since my owner's manual says to. I'll also use a bottle of Techron every oil change.

04-23-10, 03:05 PM
I did have some idle flucuations when I sprayed carb cleaner under the intake manifold next to the TB. What next? If there is a crack, what should do?

04-23-10, 04:25 PM
I did have some idle flucuations when I sprayed carb cleaner under the intake manifold next to the TB. What next? If there is a crack, what should do?

Replace the plenum. I think there is a procedure with pictures in the Tech Tip section.

EDIT #1 : Found the link to the thread: http://www.cadillacforums.com/forums/cadillac-tech-tips/171319-2000-northstar-plenum-replacement-steps.html

04-23-10, 08:03 PM
The plenum is a dealer only part, I think.

04-24-10, 12:28 PM
It is a dealer part - $43 or so. The part number is on the yellow tags in the pictures.

Might as well get an intake manifold seal set while you're there. Use the posted link and read up on the change and torque procedures.