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Mine is full tank or empty, worse when warmed up, and never at WOT, only under medium to light throttle load. Never had problem til I changed plugs, so I R&R'd them with new dub plat Autolites (again) and it went away for a couple days. Just returned yesterday driving home. It seems to start when the a/c is on, then gets progreesively worse. But never had a CEL. Ken


Ken, 99 Silver Frost SE Zetec Atx, polished alloys, Kumho's, Pioneer hi power CD/AM/FM. Factory spoiler (added) Audi side lites, Borla stainless steel muff. Stolen, recovered in pieces. Looking for another Tour, preferably V6, 5 speed.
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Originally posted by Kennard:
Mine is full tank or empty, worse when warmed up, and never at WOT, only under medium to light throttle load.




Describes mine perfectly. Dealer already replaced the IAC and there was no change. Someone suggested the TPS, that seems reasonable. I'll do some more research on this DPFE sensor too . . . the only other cause would be if the dealer either didnt install or bleed the clutch correctly . . .

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ummmm...hate to be the "bearer of bad tidings" but I had the same problems that everyone here is discussing.....then the car literally died on the highway!! It started with the small bucking, then it became more and more frequent until the car began bucking and stalling getting onto the highway monday morning. After 5 days (and countless calls) I was told that the fuel pump was shot. One of the techs at the dealership was curious....did I always try to coax "extra mileage" out of the car when the low fuel light came on? I said I did, and on a regular basis, as everyone knows how pessimistic our fuel guages are. He said he wasn't positive, but that it could have been a contributing factor in my fuel pumps demise(with the fuel sloshing around a nearly empty tank, it does make some sense;a dry fuel pump pick-up is not a good thing). He also mentioned something about the pick-up screen that is on the pump itself(which I don't think I could get to with my "returnless" 2000)And believe me, i tried EVERYTHING you guys had done, short of ripping the engine apart, to address the problem.


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Well I was mistaken on the amount in the tank thing. It is evident at all times but more so when the car is still cold. As it warms up it seems to get better but doesn't all together go away. I'm wondering about O2 sensors but that would throw a cel right? Even with headers on a 95 correct?


Green 96 mystique gs 4cyl mtx 16.9 in the 1/4 mile @102500 miles 95SE in Midnight Red MTX MSDS headers and y-pipe SVT exhaust SVT UIM Optimized se TB. Full pre 98 SVT body kit 15.741 @ 87.73mph :)
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To further my atemps to diagnos this issue. I pulled the pcm fuse. the car still is not cured and the problem was there imediately. So that tells me it is mechanical and not "learned" When I try to rev the engine in neutral it stumbles till about 3000rpm then goes about its business as per usual. You can really hear it through the intake when it is stumbleing. Gonna clean the maf this weekend and the UIM but I'd be surprised if that cleared this up. Anymore sugestions?


Green 96 mystique gs 4cyl mtx 16.9 in the 1/4 mile @102500 miles 95SE in Midnight Red MTX MSDS headers and y-pipe SVT exhaust SVT UIM Optimized se TB. Full pre 98 SVT body kit 15.741 @ 87.73mph :)
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I had similar bucking problems on a previous car. Any time I lighltly tipped into the throttle with a gear engaged, the car would buck and lurch forward. Not nice unless you want coffee stains on your shirt.

The problem was a crack in an intake hose between the MAF and the throttle body. This crack let in enough unmetered air to throw off the fuel:air mixture significantly at part throttle. WOT was never a problem because the amount of unmetered air relative to metered air was very small.

Anyway, a little duct tape on the intake pipe eliminated the bucking, and verified that that was the problem.

So, for all you with bucking problems, I would look for a source of unmetered air.


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Originally posted by Munson:
I had similar bucking problems on a previous car. Any time I lighltly tipped into the throttle with a gear engaged, the car would buck and lurch forward. Not nice unless you want coffee stains on your shirt.

The problem was a crack in an intake hose between the MAF and the throttle body. This crack let in enough unmetered air to throw off the fuel:air mixture significantly at part throttle. WOT was never a problem because the amount of unmetered air relative to metered air was very small.

Anyway, a little duct tape on the intake pipe eliminated the bucking, and verified that that was the problem.

So, for all you with bucking problems, I would look for a source of unmetered air.



i'll check that out, i have a similar problem with the hesitation or bucking but i also have my engine light on also. i posted in the trouble shooting section, please check and give some 2 cents.


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Originally posted by Munson:
I had similar bucking problems on a previous car. Any time I lighltly tipped into the throttle with a gear engaged, the car would buck and lurch forward. Not nice unless you want coffee stains on your shirt.

The problem was a crack in an intake hose between the MAF and the throttle body. This crack let in enough unmetered air to throw off the fuel:air mixture significantly at part throttle. WOT was never a problem because the amount of unmetered air relative to metered air was very small.

Anyway, a little duct tape on the intake pipe eliminated the bucking, and verified that that was the problem.

So, for all you with bucking problems, I would look for a source of unmetered air.




i'll check that out, i have a similar problem with the hesitation or bucking but i also have my engine light on also. i posted in the trouble shooting section, please check and give some 2 cents.


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sorry for the double post, the computer is being dumb


I'M RICK JAMES BITC#!!!!!!!!!!!!
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I won't be using duct tape, but I will look for leaks - thanks.

I tried re-gapping the plugs last night. Problem got worse when I opened them up to .056. Problem was less severe if I pushed the gap down to .050, but still present.

During this process I noticed that the forward bank of plugs seemed a bit fouled compared to the plugs by the fire wall. I'm gonna try an O2 sensor change - they're due anyway.

In the weeks leading up to this problem, I also noticed a little "dead zone" in the throttle. A spot that I hold the throttle at cruise. When I push the throttle through this little area, I would get just a bit of hesitation. If the O2 sensors don't work, I'll get it hooked up at the $tealer next Friday & see what they come up with.

Originally posted by Munson:
I had similar bucking problems on a previous car. Any time I lighltly tipped into the throttle with a gear engaged, the car would buck and lurch forward. Not nice unless you want coffee stains on your shirt.

The problem was a crack in an intake hose between the MAF and the throttle body. This crack let in enough unmetered air to throw off the fuel:air mixture significantly at part throttle. WOT was never a problem because the amount of unmetered air relative to metered air was very small.

Anyway, a little duct tape on the intake pipe eliminated the bucking, and verified that that was the problem.

So, for all you with bucking problems, I would look for a source of unmetered air.




Must be that jumbly-wumbly thing happening again.
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