06 GT bucking lightly when hot

Hey All, I've read about a few similar problems, but most sound like not 100% same symptoms. I recently bought a 2006 Mustang GT, manual, 95k miles. Seems to be very stock mechanically and mostly original parts besides being straight piped and had K&N drop in air filter.

It runs good when cold and for first 5 minutes driving. Then it starts to seem to "miss" and can have a few bucks when accelerating lightly-moderately. Does not seem to have an issue with hard acceleration. Most noticable problem is when it's been running awhile, and just cruising at a steady speed, it will continually buck lightly... like your being pushed very lightly about 1.5 times per second. When I come to a stop and it's idleing, the rpm are steady, seems fine at idle even when hot. Happens in all gears/speed... don't remember it being as noticeable at very high speed.

I'm not very experianced at diagnosing, can do minor repairs/testing. Was thinking it may be a weak spark in a cylinder. Had Ford dealer put in new spark plugs, also asked them to put in new fuel filter. I changed the engine air filter(oem).

Ford didn't replace the coil packs, so I bought one coil pack and tested it using multi-meter, between pins and between pin and coil. Tested each of my original coil packs and they are all close to the same.. so probably not bad coil pack.

Going to do an oil change this weekend. I have a cheap scan tool, shows no codes when starting the car... maybe I need to have it plugged in while driving - will try this. If oil change doesn't solve it, what should I check for my symptoms?

I've read about trying some chevron fuel additive, will look for this.

Thanks!
Deonild

Hey All, found some similar posts and I'm getting some ideas of what I can check. Haven't found a post with my exact symptoms. I recently got an 06 GT manual with 95k, mostly stock besides straight piped.

I'm not very experianced at diagnosing, but can do minor repairs/tests.

It runs good and smooth when cold and for first 5 minutes of driving. Then after it has warmed up, when cruising at a steady speed it's constantly lightly bucking/jolting about 1-2 times per second, like being nudged or being in a massage chair. Not extreme and no loud noise, but enough that it can't be ignored. It may buck/jolt during light-moderate acceleration but seems good during heavy acceleration. It seems OK when coming to a stop/ideling even after being driven for a long time. Tachometer is steady at idle and while cruising. Does not increase frequency based on wheel speed, seems based on engine.

I replaced engine air filter, and had Ford replace spark plugs and fuel filter. I tested coil packs with a multimeter between pins and between pin and coil and they're all very similar so probably not the issue.

Going to change oil this week. Another post mentioned Chevron fuel additive I'll take a look for.

Any ideas what I should check next or possibilities for my Mustang's symptoms?

Thanks!
Deonild

I made two threads by accident, this one and "06 GT not smooth when hot". This first thread looked like it disappeared. Mods, you can delete/merge this thread.

Thx,
Deonild

My cheap scann tool shows no codes, I'm going to ask an auto parts store to check also.

Also forgot to mention, I cleaned the mass air flow sensor and throttle body with appropriate spray cleaners, so thats not it.

Did oil change today, didn't resolve the issue. It's hardly noticeable above about 1,600 rpm. At that point I can hear a faint hum coming and going but not feel the pushing.

I doubt if previous owner reprogrammed, maybe that could cause as noticeable of an effect as this?

So this is my first manual car. I think it's a combination of me shifting too soon, and the computer not being tuned for the straight pipe exhaust. It runs fine if I keep it around 2k-2.5k rpm when cruising, is that normal for 2nd, 3rd and 4th gear cruising? If I'm shifting too soon and lugging the engine not sure why it doesn't happen when engine is cold.