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Car shakes/throbs at idle, but no misfire error codes
My car shakes and throbs at idle, regardless of gear. The problem started after I changed out the battery a couple months ago. I've tried a throttle reset which seemed to greatly improve it, but a month later it started again. Seems more prominent when the car is warmed up. Two of the cylinder's spark plugs have never been replaced (200k miles lol) so they seem like a logical choice, but Ive never gotten any error codes about misfires.
throttle body was cleaned thoroughly 2 years ago, MAF has been cleaned, I tried Seafoam in the fuel/oil.
Can anyone think of another cause of shaking at idle?
Also, how hard is it to replace the two rear-most cylinders' spark plugs? I've heard they're quite lot harder to reach than the front 4.
Many people say the plugs are hard t replace, but I've never had much of an issue.
If you do another throttle rest, does it get better again? If so, I'd get a proper diagnosis on the to see if you have a problem with the accelerator pedal.
I performed another throttle reset and went for a drive around town ~30 mins, no change. I cleaned the MAF for the heck of it and also no change. I'll replace the sparkplugs in 2 weeks when I have time.
In the meantime, does anyone have any other thoughts on what causes this shake? I've noticed that if I hold my foot on the accelerator and rev up slightly to 1,000 rpm, they fluctuate quite a bit, by about 200 rpm up and down. I'm pretty sure the shaking is caused by the engine revving up and down, if I reduce pressure on the break while stopped, the car will creep forward a bit in sync with the throbs.
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
Replace those plugs. At that mileage & the fact that a throttle reset made a short term change my suspicion, if the MAF is fine & you have no fuel trim codes is that the throttle body actuator is suspect. Take off the throttle body & remove the black plastic actuator cover & clean up tracks etc with switch cleaner. If that does not fix things you might be in for a new throttle body. Old worn throttle bodies can go into oscillation that messes up the idle.
What happens if you engage your aircon at idle?
Does your temperature gauge operate normally? A bad temp sensor can mess with closed/open loop mixture control hot but I would expect fuel trim codes.
code scan revealed P0400 EGR flow error "pending". So i suppose the next step is to remove and clean the EGR valve. Will post results after I clean it.
So I attempted to take apart the EGR valve but was stymied by the nut holding the tube onto the valve body. There's a compression nut and a fitting nut under it. I could not get the compression nut to budge at all, even after soaking it in WD40 for about 30 mins. Any thoughts? I don't wanna damage the tube without having a replacement handy. Am I disassembling it wrong? I attached a picture of the tube and nut for reference.
The nut (rusted) that I can't get off. I wrenched on it as hard as I could for awhile, but only bent the pipe.
also, does anyone know how to get that black bracket off? it's in the way, and I can't feel any bolt holding it on, underneathe the EGR. (its the bracket that holds on the oil tube and battery wire)
unplugging the vacuum line that actuates the EGR valve fixed the symptoms, so I think the valve might be gummed up with exhaust buildup. In a week or so I'll have access to the tools to take it apart, and hopefully I can clean the whole thing up.
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