Bucking??
 

86 GT H.O. 5.0EFI, 5spd.

It doesn't matter if I'm cruising through town or on the highway, sometimes when I let off the gas at lower rpm (less than 2200) the car bucks. It doesn't do it all the time, but enough to bother me. Sometimes while cruising at 25 to 35mph it will also 'buck'.

Any Ideas. I cleaned the IAB recently, complete tune-up about 10k miles ago. Mods are Hypertech chip and cat-back exhaust.

Thanks,
Jeremiah

i would say a small vacuum leak, when you let off the gas the motor is trying to rev up for a sec. then bucking, either that or you just need new u joints

Get a DMM w/ a bargraph
 

You need to inspect your TPS. Disconnect it at the harness, and attach a DMM to the TPS green and black pins. Set the DMM to ohms, and watch the bargraph while you SLOWLY rotate the throttle. If the bargraph jumps backwards at all, replace it. It should gradually increase, very smoothly.

Take care,
-Chris

if your prob ends up being the tps you should set it at idle and it should be about .95 -.98 just make sure that it isnt above 1 volt, hope that helps you.

I had one guy tell me it was a fuel thing, because my car runs a little lean below 3300 rpm, a/f is at like 16 below 3300 and just a hair over 14 from 3400 to 5600rpm. I bumped up the fuel pressure and it still bucks at really low rpm like yours, usually on decel but also if I'm trying to coast in gear. Another friend told me it's the cam. I'm running the TFS Stage 1 and he said i might need a chip to smooth it out. I'd already checked my tps and it was set at like .985 so I think that was fine.

I don't know either way so I've decided to do my level best to keep the rpms up so i don't have that problem.:D

Driving at a low rpm in a car with a cam, the car will buck sometimes. Thats normal with a cam. Your car is also running lean from the a/f readings you posted. In the upper rpms, low to mid 13's is considered the norm a/f for n/a cars. I have the TFS 1 cam and it'll buck sometimes in a low rpm in a high gear, but mine doesnt seem to do it like your does. Whats the rest of your combo? Sounds like it needs tuning.

GRN92LX:
I just installed the exact same combo you have. Are you still using the stock 19# injectors? What fuel pressure are you at? My car is also bucking like a mule at low rpms.

I'm running 24# bosch injectors. They are flow matched. Playing with fp at the track, I have found 37psi to be best for my car. I havent played with timing at the track yet. My car doesnt buck much, but like I said lugging the engine with a cam will make it buck like your describing. Cant really help with fp for 19# inj, but at the track, try 43-45 psi and see how mph is affected when you change it.

I also have bucking at low rpm's. i've done all the tunings that would relate like timing, tps, fp. it helped some but it still bucks a little bit. i'm thinking it's partially my combo and my u-joints.