Light Accel stumble - no codes

[erupert66]

I have a '99 LX-470 with 264K that I have owned since new. My wife is the primary driver and recently she said it's been "jerky". Every once in awhile, it will be a bit rough on cold start. That goes away after maybe 30 sec or some higher revs. I drove the truck last week to see what she was talking about and it's a bit strange, when driving in town and pressing the throttle lightly it seems to "buck" a bit but feels like it's in the drivetrain. I have no codes. About 2 years ago I lost a coil pack but other than the spark plugs and a TPS sensor, it's all original under the hood. (check that - O2 sensors were changed about 6 (driver) and 4 (passenger) years ago. I have cleaned out the throttle body maybe a year ago.

I do have a WIFI OBDII transmitter and engine management s/w if someone has some ideas on what to look for. I had some issues like this with my '95 F150 and it was related to the EGR valve. Since I am getting no codes, I am not sure where to start.

Thanks

 

[Mach5]

I'd start with some really simple maintenance under the hood and see if it clears things up. MAF sensor and throttle body cleaning again. Maybe try a fuel additive like gumout or stp to clean the injectors, fuel system. Is there a delay in the throttle when you get that bucking sensation? Some aggressive driving might throw a code where it otherwise wouldn't show up, ie: high rpm acceleration. Start small and simple and work your way toward the more expensive solutions. Good luck.

 

[aljollano]

Same symptoms two weeks ago and finally gave me a code. It was P0305 missfire on number 5. Replaced the coil pack for number 5 and replaced all spark plugs. It runs really nice.
A.J

 

[erupert66]

Mach5 - tried to spray out the throttle body, didn't help. hooked up to a friend's meter and checked the tps for any signs of erratic movement. nothing. all other sensors seems normal (Short Term fuel trim was a bit jumpy between 11 and 8 but Long Term was about 4.5).

Thanks. I replaced one coil pack about 2 years ago. All others are original. Interesting thing is that if you floor it, it goes away and it's very erratic. I ran the tank down near empty and put some Gumout and 10gal in the tank. so far, hasn't done it since. It also seems a bit more responsive on the throttle, seems a bit "boggy" on med acceleration. Wife is driving my car now so I am driving it for a week or so to see if I got lucky with some clogged injectors. Otherwise, I'll buy one coil pack and move it around.