95 GTS - Engine Bucking at low speeds

[doctorj357]

Curious as to what your thoughts are on my current setup (1995 GTS 5spd). I am the 2nd owner of the car. All this work was done back in late 90s. Car runs pretty good actually, but have noticed some bucking in the engine at low speeds that's kind of annoying

Intake Manifold / UPPER Edelbrock / Performer PN: 3821 70mm
Intake Manifold / LOWER Edelbrock Performer PN: 3820
Intake Adapter for EFI - Edelbrock PN: 3835 70mm
Throttle Body - BBK / 65mm PN: D-215-19
Cold Air Intake - BBK / 70mm PN: 1712 (new filter)
Heads - Edelbrock / Performer PN: 60379 [1.90 Intake]
Ford Performance / E303 PN: M-6250-E303
Manifolds / Ford Motorsport stainless shorties
Gears: Upgraded to a 3:27

So can't tell if the bucking is due to characteristics of the cam, or am I possibly experiencing a bottleneck on the intake cause of the 65mm tb. Scary part was the car was never tuned. And frankly amazed the stock ecu could compensate for such mods. Now that I recently added a SCT Chip with BAMA tunes on it with my mods its much better. But the bucking issue never really improved or went away. Like when going 25-30mph in 3rd its almost impossible to do it smoothly and gets annoying quickly.

Just curious if anyone ever ran this setup, or a 65mm tb and had similar issues. I'm sure by going to a 70mm TB will only improve the overall performance of the car. How measurable it may be is debatable and only would show up on a dyno maybe. But this isn't a track car and am really looking to make it into a cruiser.

 

[VibrantRedGT]

Not the best cam for the 94-95 ECC, it likes 113+ split duration for smooth idle.

May want to throw a code scanner on it even if you're not getting a check engine light. I got a 564 last night with no CE light.

I also got a code 121 inproper TPS voltage which is why my idle is surging and the TPS is usually the culprit for what you're experiencing.

The ECC likes .98V, anything over usually cause some bucking in my experience.

There are lots of factors but I'd start here.

Also go over the surging idle checklist. Lots of good info there.

 

[General karthief]

When you check the tps make sure the sweep is smooth, with your meter attached open the throttle slowly and note that the numbers increase with no dropping or skipping around, mine had a dead spot at about 1.3 to 1.8 that caused it to buck at low speed.

 

[NIKwoaC]

What RPMs is the bucking happening at? By "bucking" do you mean an idle/sputter problem, or do you mean it in the more conventional sense where you get the on-off-on-off drivetrain slap sensation?

It's not uncommon for these cars to get the "drivetrain slap" bucking when trying to creep below ~1500 RPM or so, and it typically gets worse with modifications. My car did it when it was still completely stock.

 

[jrichker]

You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the [URL=" http://forums.stangnet.com/showthread.php?t=698148"]Surging Idle Checklist[/URL]. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix.

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 250,000 hits, which indicates it does help fix idle problems quickly and inexpensively.

 

[Steel1]

My guess is it's tune related, possibly rich/lean afr swings.
I'm in the process of tuning out a low speed buck on my 93GT Pimpxs set up,
with the help of a91what

 

[doctorj357]

So last week I dialed back the timing from 15deg btdc to 10deg, incredibly smoother at low rpms now. As for surging idle, I also removed my SCT / Bama chip and went back to the stock ecm, for now. Seems to run, well just better. It'll get an appropriate tune eventually but for now this will work.