Today I was driving around in Washington and came to a stoplight. I put the car in neutral. My idle went all the way down to 100rpm and sputtered just right around there sounding like it was just about to slow down until it stopped. It just idled from <100-200 back and forth until the light turned green and I went on my way. I thought it was like this one time thing and thought of it as pretty weird.

Then I go park in the parking garage. I stop in a spot and I see another case of this weird idle. 750. 850. 750. 850. 750. 850. etc. And it was just going up and down up and down like a pendulum.

What could be the cause of this? My engine and car for that matter is completely stock. I did have some work done to it awhile ago from a stupid misshift over a month ago. Any suggestions appreciated.

 

I believe the misshift is to blame. What work was done on the car?

 

what work was done

 

I'm gonna go ahead and guess valve replacement... sputtering under idle could possibly be affected by valves not seating correctly but if that were the case, it would be present under throttle as well. Another possibility would be that one or more of the valves were not replaced for any number of reasons and b/c of that, some of your cylinders isn't getting the same A/F as the other causing the change in rpm. It is higher (or lower, doesn't matter) on normally functioning cylinders but when it comes time for the damaged cylinder to turn the crank it doesn't create the same amount of force. Ok, done hypothesizing... tell us what work was done after your mis-shift.

 

I think the Valves were straightened and rocker arms/bolts were tightened. It was my father's mechanic who did the work and I have yet to talk to him. He tore apart the block though. The extreme ticking went away. It really does **** me off not knowing exactly what was done to my motor. But I'm not going to complain for having free/quality work done. I'll try to see exactly what was done. I just know nothing major.

 

was the car warm or cold? sometimes when it does that the thermo wax valve.
to fix it, look on your intake manifold and you will see a cover about the size of a fifty cent piece take the two screws out and there is a valve in there with a slot on both sides, use a flat head screwdriver and turn the valve all the way down that probably will fix your problem.

 

could your mechanic have missed a vacuum line somewhere?