Engine Infamous "bucking" problem!!

rocksolid

Member
Jan 24, 2019
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Dayton, OH
Whats up guys? My car has been acting a fool for the past week. It all started with dying right when it first started for the day, but then running perfectly fine the rest of the day.
As things went on, this turned into a rough idle, bucking at around 2000 rpms... I went through the check list a few times and have tried to work out as much as I can between work and everything. I don't have a test lamp to pull codes, but I'm doing that tomorrow and I'll post the results. But between now and then I figured I'd ask for some thoughts.

So far, this is what I have done.
New PMAS calibrated MAF because I have 24lb injectors with no tune for them.
New air filter
New IAC
New MAP/BAP sensor
(IMPORTANT PART): New fuel filter, because I realized mine was leaking... Ran like a million dollars all day after, and now bucking again.
New cap, rotor button, spark plugs, and wires.
Deleted the EGR valve because it was cheaper than buying a new one in case that was the problem.

Next on my list is probable a TPS and oxygen sensors. After that, I really have no idea what it could be.

I should also add that I work at a parts store and I get this stuff for ridiculously cheap, so I didn't mind chasing the grimlin too much. But now it's getting ridiculous. Any thoughts on what I should be looking at?
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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The surging idle checklist. These cars require diagnostic procedures that if not followed step by step you can waste time and money as you have found out. Also you don't say what year your stang is and any other modifications.
 

rocksolid

Member
Jan 24, 2019
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Dayton, OH
You’re right! It’s a 1988 LX with light-ish mods. BBK ram air intake, B cam, mass air conversion, no smog pump, and a flowmaster exhaust setup.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
17,310
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polk county florida
I believe the surging idle checklist http://forums.stangnet.com/showthread.php?t=698148 covers nearly every possible scenario that would cause this, I will add that when I had the bucking issue I found that my tps was freaking out between 1200 to 1800 rpms, it should sweep smoothly from idle (9.6/10.4 on a volt olm meter) to wfo, the volt numbers should rise steady to max, mine would bounce to zero between 1200 to 1800 rpms, that caused the car to buck violently in that rpm range. The checklist also covers the proper procedure for resetting the computer if necessary.
jrichker is to blame ahhh, I mean thank for putting this together with added imput from other members. It works!
 

7991LXnSHO

Now I want a 10 year badge
Sep 1, 2010
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Even with OBD1, you are wasting your time (and ours) without checking codes and going through that list. Please read it several times, start down it, then send us codes when you get there.

The diagnostic procedures are better than what new Ford stealership mechanics know about now. You can be the local expert, soon.
 
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Reactions: General karthief

rocksolid

Member
Jan 24, 2019
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Dayton, OH
Just an update because I feel like no one ever updates these threads after they fix the problem:

I was misfiring all over the place, and throwing codes for oxygen sensors. I replaced the oxygen sensors. It was still running pretty rough and misfiring. I dig around a bit and discovered that my timing chain was VERY loose.

So that was a lot of fun. I replaced the timing chain, and threw in a new water pump just because. While it was jacked up I decided I might as well put in a new oil pump too, hoping that I won’t have to unbolt the engine for a very long time.

After a new chain and adjusting the distributor, she runs beautifully!!! Now maybe I can focus on some fun stuff like making her look good and going faster! Haha
 
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