Trying to figure out what is wrong with my 2011 GS convertible with 6-speed. Washed car today, dried it, and took it out for a spin. Drove easy at first and warmed up the oil and the engine. Then I opened it up a bit (maybe 3/4 throttle) in second and third gear. When the RPMs got to around 4500-5000 in third there was a sudden stumble or stutter in the engine that shook the car. I backed off the throttle, but saw no codes set and no sound of engine distress. The engine sounded good. Did the same routine and all well up to 6000 RPM. Tried a third time, and the stutter/stumble returned. Again no codes set or other issues, just a 1-2 second stutter /stumble that shook the car. Then all is fine.

Engine temperature was around 200F and oil temperature 228 F. Outside temp about 60F.

Tried this another half dozen times, and maybe one time did the stutter/stumble repeat. The rest of the runs the car pulled strong to 6000 RPM without issues. But I did notice (maybe) a little roughness at idle after when sitting at a stoplight or at a stop sign.

I plan to take the car out in the next few days on an open highway and see if the problem returns.............but without any codes or anything else out of the ordinary, it has me baffled. When I put it away for the night in the garage, the engine sounded good and normal.

Wondering if maybe the throttle sensor is hanging up, MAF acting up, maybe one of the engine sensors going out, or ??? It does not always repeat, seems to occur at around 3/4 throttle and 4500-5000 RPM, and is too great/large to be a single cylinder misfire. Nothing heard out the tailpipe indicating a misfire. I have not done a full throttle run at this time due to traffic congestion.........mainly just playing a bit with the car as traffic permits. I think you get the idea.

If I can't get it sorted out on the road, the only other possibility is to put it on a chassis dyno to see what that shows. But finding a place I trust with a chassis dyno may take some time.

Any advice is appreciated ??

Larry

 

Check plug wires. Make sure they are tight.

 

A chassis dyno ?????...get yourself a scan tool cause it may help you to diagnose it...don’t know your mechanical abilities but it may just be cheaper to pay for an hour diagnostic time.

 

I'm pretty much "old school" and feel more at home with the C1/C2 and perhaps C3 cars. But I have both owned and driven the later models. I do all my own work on the early cars.

I felt that if the malfunction could be duplicated on a chassis dyno, then air/fuel, timing, power drop-off, etc could be more accurately defined..........which could hopefully lead to a solution. Maybe the scan tools will work, but problem only seems to occur erratically and under load. A review of the archives the last few hours shows these possibilities:

1. MAF dirty - maybe
2. Knock sensors issues-rapid timing change. It is possible something got wet during the car washing. Or one is going bad. Should set a code.
3. Deceleration Fuel Cutoff.......didn't even know this existed. Maybe.
4. O2 sensor - maybe, but it should set a code.
5. Traction Control activating........this is very possible as I have older Bridgestone Protenza track tires (rubber now getting hard) and air temps tonight were cooling down with high humidity in the air (making slippery road conditions)

Best thing is probably another "test drive" under daylight conditions on a straight and open road.

I appreciate the comments so far. I know very well what a loose/broken spark plug wire can and will do to this car. Been there before, and this was definitely not it.

Probably doesn't matter, but car has only 17,000 miles and essentially factory stock. No engine mods or tunes, etc. Again, suggestions or comments on my "possibles" list.

Larry

 

You may have to have the car on a dyno for hours for the issue to return and I don’t know how much that will cost and even if it does I highly doubt that the operator would be able to diagnose a TPS issue which it may be because you would need to scope the signal wires (you can not see the voltage drop outs with a multimeter) and again the operator probably doesn’t have one...you can try cleaning the MAF sensor and maybe the TB...all of the other things I would use a scan tool for...you just have to be able to interpret the live data you’re seeing...I enclosed a video so you can see why these days you have to use a scope...the gentlemen is one of the top automotive instructors in the country and also has a diagnostic shop too...he’s old but not “old school” when it comes to diagnostics...LOL !!...good luck !!

 

Thank you.........

Larry

EDIT: The video was pretty much what I envisioned doing on the dyno............but I agree that additional electronics are needed for this testing. The dyno setup was primarily to load up the engine at the 4500-5000 RPM while monitoring the scoped data. So my concept was right, but my terminology was wrong/lacking. Probably too old anymore to change.

Any comments regarding the traction control??