My 2003 Northstar SLS, 65K milesruns a bit rough at idle, sometimes a slight surge. I may be imagining things, but it seems to surge or hang while driving down the road at speed.
The car starts fine, hot or cold. The rough idle get worse after running at idle for more than 20 seconds or so.
No check engine light.
I have changed the spark plugs, air filterand cleaned the IAC, which only had a slight dry carbon build-up. Not much improvement.
I also checked around to see if any vacuum hoses were broken or disconnected but could not find any.
I would appreciate any suggestions.
After looking on auto parts websites, parts for this car aren't cheap!

 

bump

 

Codes stored? May need scanner to read ecm data to find cause.

 

02 sls 120k , i am having the same problem and have replaced plugs,air/fuel filters,IAC, and checked for leaks the best i could as well as seafoamed/cleaned intake/throttle body all with no effect other than a small gain in throttle response . i keep trying and failing. a few months back the car was running fine, then one day the idle stared goin crazy on me, one minute the idle would be so low i would have to hold my foot on the gas just to keep the car running even after warming up, next minute the idle would be so high it was hard to keep the car from taking off. that problem has somewhat subsided, the really low idle problem seems to be gone.
lately the problem is the rough idle after idling for about 10-15 seconds and constant if the car is idling in gear (feels like surging when the car is in gear). occasionally when i stop the car and put it in park the idle will shoot up around 1800+ rpm and wont bring itself back down for minutes sometimes (i usually turn the car off as soon as i see this start to happen and restart and all is well aside from the rough idle).

my check engine light is not on and i just pulled the codes tonight with nothing showing other than a couple abs codes for the brake wear indicator.

I am puzzled as to what could be causing this and would really appreciate any assistance anyone could provide, this problem is driving me crazy.

 

Without guessing with more parts, it would be worth while to have it scanned by a qualified tech. Scanning is different from code reading, some would call a "Diagnostic". TPS is a possible cause, but it is a guess.

 

i think i found my problem, the intake plenum (boot) is leaking on the bottom . im ordering the plenum tommorw along with a manifold gasket because i believe you would have to r&i the manifold. looks pretty straight forward. although if anyone would know what the procedure involves specifically that would be a great help

 

or at least how much to torque the manifold bolts. im sure even at my cost the manifold wouldnt be cheap

 

try the idle speed control they can fail and not trip the engine light cuase of a problem inside it

 

i believe that this usually is a gasket problem and you would need a new gasket.


i agree..


additionally, a vacuum leak somewhere can affect the idle.





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Hi I had a similar problem. Changed my idle sensor and coil pack. Car has improved a lot. No more rough idle and no more cutting off.

that the ignition coil I changed.