I've got a 2001 Saturn SL 5 speed. It just started doing this a few days ago.

https://www.youtube.com/watch?v=_EXS...ature=youtu.be

It only does this at idle, and only after it comes up to operating temperature. Plugs and wires have been replaced sometime within the last ~year or so. No check engine light. No codes. Idle is ~950 RPM and doesn't fluctuate. Gas mileage doesn't seem to have suffered any since it started acting up, and it doesn't seem to struggle to accelerate any more than you'd expect from a ~90 horsepower 4 cylinder.

In other words, what I'm trying to say is it runs fine, it just has what sounds like a misfire at idle.

I've pulled the EGR valve and cleaned it. I've unplugged the O2 sensor to put it in open loop to see if that had any effect. Neither of these things changed anything.

Edit: It just now decided to throw a code. P0302

 

Switched plug wires around. Misfire still on #2

Switched spark plugs around. Misfire still on #2

Switched ignition coils around. Misfire still on #2

Noid light tested #2 injector. Signal tested fine. Misfire still on #2

Switched fuel injectors around. Misfire still on #2

 

How about compression across all cylinders?

 

Try this. With the engine idling, spray some WD-40 around the intake manifold gasket on the upper outboard area around the #1 cylinder port. Also check around #2 but #1 is where this engine has a history. That corner of the intake port is not supported and it can suck the gasket in in this area.

The high idle with the miss is the big clue here. WD-40 will temporarily block the leak and the miss will disappear for a few seconds.

 

Did a compression check. Fuel relay removed and ICM disconnected.

Cylinder 1 - 120psi
Cylinder 2 - 130psi
Cylinder 3 - 150psi
Cylinder 4 - 155psi

Sprayed carb cleaner around the intake manifold around #1 and #2. No change in idle.

 

Damn for whatever reason I thought it was an sl2 but your post says SL. My bad.

Keith is spot on regarding the intake manifold leak. Your idle is ever so slightly high so it may be a very very tiny leak at #2. I would douse that area again as to find the leak. ,The compression numbers are pretty low. Service limit is 185. How many cranks do the cyls take to get to those values?//specifically does #2/take significantly more cranks than the rest?

 

I realized last night after I'd decided to wrap up for the night that I screwed up when doing the compression test. I didn't have the throttle opened up while cranking. Redid the test with the throttle open this morning and got the following numbers.

cyl 1 - 160 psi
cyl 2 - 160 psi
cyl 3 - 180 psi
cyl 4 - 155 psi

They all got there in about the same number of cranks.

 

You doing a wet or dry compression test?

 

My car intermittently does the same thing, but it is only at idle, and only when the transmission is in a drive gear. In park or neutral, it idles correctly. I have a check engine light, but haven't had the opportunity to have the codes pulled