occasional rough idle...
#1
05-07-2007, 11:03 PM
occasional rough idle...
Reposting this since 'Tech' is back....
2002 s40. 70K miles. Car runs fine except if in very heavy, very slow moving traffic, after 30 - 40 minutes, the car will start to idle rough. Start as a slight shudder and gets worse to where it wants to die. If I put it in neutral and give it gas to keep it running, the tach will go from say, 1500 where I am holding it up to 2000, down to 1000, up and down. If it does stall, it will start up again. As soon as traffic clears and I get up some speed, its fine. And it will restart and drive fine. There is a real hesitation (like almost 2 full seconds) of no throttle response when giving it gas to get it moving when this happens. Also, rarely, the rough idle will start when starting the engine on a hot start. Only codes that have been thrown are for either random or multiple cylinder misfires. Worst (and first) time this happened, the car died and would not idle unless you were giving it gas. We cleaned the MAF & IAC and that seemed to sort it out for awile.
Mechanic is trying to rule things out rather than throw parts at it. So far, he's cleaned the maf, throttle body and IAC. Also new air filter and full fuel system cleaning. Overall performance was much better but original problem still occurs if sitting in the heavy traffic. Next thing hes thinking is to replace the IAC.
Any thoughts?
Fuel pump seems good. Doesn't seem like a vacuum leak. FPR? Fuel filter?
Thanks!
2002 s40. 70K miles. Car runs fine except if in very heavy, very slow moving traffic, after 30 - 40 minutes, the car will start to idle rough. Start as a slight shudder and gets worse to where it wants to die. If I put it in neutral and give it gas to keep it running, the tach will go from say, 1500 where I am holding it up to 2000, down to 1000, up and down. If it does stall, it will start up again. As soon as traffic clears and I get up some speed, its fine. And it will restart and drive fine. There is a real hesitation (like almost 2 full seconds) of no throttle response when giving it gas to get it moving when this happens. Also, rarely, the rough idle will start when starting the engine on a hot start. Only codes that have been thrown are for either random or multiple cylinder misfires. Worst (and first) time this happened, the car died and would not idle unless you were giving it gas. We cleaned the MAF & IAC and that seemed to sort it out for awile.
Mechanic is trying to rule things out rather than throw parts at it. So far, he's cleaned the maf, throttle body and IAC. Also new air filter and full fuel system cleaning. Overall performance was much better but original problem still occurs if sitting in the heavy traffic. Next thing hes thinking is to replace the IAC.
Any thoughts?
Fuel pump seems good. Doesn't seem like a vacuum leak. FPR? Fuel filter?
Thanks!
#4
03-14-2008, 12:29 AM
RE: occasional rough idle...
I seem to have this same issue.I have been told IAC, ERG(exhaust recycle gasket?) throttle body, or clogged air filter. All of these are solved by cleaning or replacement and all of them seem to cost almost nothing to replace. I drive a volvo 960 with 212k miles on it.
#5
03-17-2008, 09:20 AM
RE: occasional rough idle...
Man I hate throwing parts at a problem. Just hurts to spend money when it's not needed.
What do your plugs look like? (I'm talking reading the plugs for signs of how the combustion process is occuring like black for rich, etc)
How about your fuel pressure? You could hook up a fuel pressure tester and crank the car to check for a bad fuel pressure regulator.
What do your plugs look like? (I'm talking reading the plugs for signs of how the combustion process is occuring like black for rich, etc)
How about your fuel pressure? You could hook up a fuel pressure tester and crank the car to check for a bad fuel pressure regulator.
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