markd

I did a quick search for the answer to this problem, but the closest I have found is a detonation or timing issue at idle, so pardon me if this topic has been discussed before. Feel free to direct me to the proper thread

I understand that a lot of 8's have 'puttering' issues at idle, but I seem to have the same problem when I'm going at various constant speeds, most often around 40mph. My car just jars forward several times, sort like it's about to sputter and die, but it doesn't sound like that at all. It jolts, as if I am pressing the gas and letting go very quickly over and over again. It eventually stops after a few seconds, but I'm wondering if this sounds like something that could be bad for the engine. Anyone else have this problem (not from idle)? As an aside, I use either 89 or 93 octane.

RX8_Buckeye

That is definitely not normal. I recommend taking it to the dealership ASAP. There might be a problem with the ignition system or electronic throttle control.

downshift

At what RPMs do you experience this problem? I don't think it is a problem, but you might want to state that to take engine lugging out of the equation.

dmp

My last car did that because of a vacuum leak. Good luck, and keep us posted if you will.

markd

This problem usually occurs at low RPMs and, again, at various (though always lower) speeds. Most often the jarring happens after I have been coasting without depressing the gas and then lightly press the gas to pick up or maintain speed (i.e., when I'm circling around in a parking lot below 15mph and then hit the gas to pick up speed, or when I let the car accelerate naturally down a hill and then press the gas when the road flattens out).

I mentioned the gas I use b/c I had used 87 octane several months ago, the ride was definitely rougher during that time, and I figured it was just another engine timing issue (I have not gone back to 87 octane since). Otherwise, it's hard to pinpoint because the jarring occurs at various engine temperatures, various speeds and not in any particular gear that I've noticed. I didn't realize it could potentially be a bigger issue. I'm also due for an oil change, although I noticed last night that the Change Oil light kept coming on and off. Hopefully that's not another concern to add to my list of headaches. Anyway, consider me halfway to the dealership!!

zoom44

but you say its mostly at low rpms so i would suggest it sounds like you are luggin it. either give a little more gas to get the rpms up or downshift.

Slims8

I guess that is a good suggestion... You mentioned it was most noticable at 40 mph? What gear are you in?

markd

I had not been paying attention to what gear b/c I haven't been able to recreate the problem consistently under the same driving conditions, but it was either 3rd or 4th gear. I guess I am confused with Zoom44's advice b/c I've ridden in manual tranny's when that has occurred but have never had that problem in an auto, which I have. Perhaps it's not a transmission-specific problem, though...?

zoom44

acck!! you need to mention things like that when you pose your questions. and i need to ask before i pose my answers. so lets back up- you have an automatic. are you in "manual mode" when this occurs using either the paddles or the stick to shift or are you letting the car choose the gear? do you have an aftermarket intake? oiled filter? had any cels recently?

markd

Sorry, Zoom! Everything on my car is stock, and when this problem occurs, I let the car choose the gears. No CEL's ever, and the only indicator light on, as I mentioned above, is the Check Oil light, which came on and off twice last night.

zoom44

and the "lugging" sensation occurs not while coasting along but when you tap the throttle to get a little more speed?

RotaryNoob

This has happened to me with my 6SPD. Its only when I'm gassing it and then let off and apply gas again and it doesn't happen very often but it does jolt. I attributed it to my intake though.

markd

That's correct.

zoom44

could be a confused pcm. its humming along just doing its thing when it gets your blip signal from the throttle by wire it thinks "oh he's gassin it, i gotta watch my a/f raritio and start to adjust that(gotta keep it at 14) and take a look at the timing(switch from reversed idle firing and should geta little advance in there) oh and i better get ready to shift" and then the throttle signal drops back down. now it has to back off the things it was just preparing when it was trying to anticipate what you were about to do. it changes back to it's idle settings but that takes a second for everything to fall back into place. that could be the "lug" you feel. just a guess. does it doi it if you've been coasting and then you just accelerate up another 10 mph etc or just when you sort of blip the throttle to push it along?

markd

Sounds like a logical explanation. It usually only happens when I blip the throttle to push it along (I've never actually tested it when I'm throttling the gas). The lugging usually dissipates after several seconds, but the fact that I hadn't experienced this at all until recently (and the fact that I feel like a retard when my car is "lugging", multiple times a week) was enough to concern me. If this is a PCM issue, I wonder if my recent M-flash recall, which I did a month or two ago, has anything to do with it...? My gas mileage has gone down a little (from about 16mpg to 13mpg or worse) as well. I asked my dealer if they could have flashed the car incorrectly, and he said it's highly unlikely.

zoom44

have you flooded? the issue also could be a clogged or clogging cat- when you ask for more power by blipping the throttle it could take a moment to overcome the pressure and get the exhaust moving out. might not be noticeable on heavy throttle input just on light throttle inputs.

RotaryNoob

Thats probably what mine is... I noticed that whenever it has been sitting for at least 6 hours and I start it the CEL comes on. Today I started it, got the CEL and was smoking a cig outside the car waiting for it to warm up. I was behind the car and the exhaust smelled like rotten eggs or very sulfery...

I'll eventually take it in. I just hate the thought of driving a focus while it gets fixed.