Fox T-Bird/Cougar Forums  

Strange missing/bucking while decelerating...

September 23, 2005, 12:30:27 PM

Hey, guys...I've just developed a pretty bad problem with my car and I'd like to get some input before I start chasing my tail.  The car runs like a raped ape under full throttle or even half throttle...in fact, when accelerating there is no problem above 1400rpm.  But, while decelerating or under light throttle(maintaining speed) between 900-1500rpm the car bucks real bad.  It was idle surging real bad and the check engine light would come on after about 10 mins of driving, but it was still very responsive and never stalled. 

Now, the idle is quite smooth at approximately 600rpm(in drive) but the check engine light will come on after about a minute once I lay off the throttle...as soon as I begin to toe into the throttle a little more it goes right off and the process continues as well as the above mentioned problem.  I'm leaning towards a MAP sensor, TPS, or something with the EGR...doesn't ping at all though, so I don't think it's clogged.  I was also thinking a possible vacuum leak, but everything seems to be in order.  Any ideas would be appreciated...I'd like to get her running good again before I dig into the heater core.

Thanks,
Don

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Re: Strange missing/bucking while decelerating...

Reply #1 – September 23, 2005, 01:06:41 PM

A vac leak would increase the idle. I have somewhat of a similar problem. My 5.0 Bird will buck at start up and almost die when I push the gas after sitting for a week. I tried adjusting the tps but it didn't help. I got a map sensor from the junk yard free (ie pocket) and stuck it on. Solved the problem. I'de try a map if ya can. Oh wait the check engine light comes on? I'de go throught the emissions stuff. If the check engine light comes on it's usually an emissions problem. Could be an egr valve after all.

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Re: Strange missing/bucking while decelerating...

Reply #2 – September 23, 2005, 11:02:15 PM

Yeah, it ended up being the TPS sensor...it was new 10k miles ago...I had the old original Ford TPS sensor from the old SO engine and it slapped it on...now it runs like a lincoln...lol(did you think i would really say caddy?).

Looks like I was figuring it out while you were posting...lol, thanks though.

-Don

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