I need some help on an annoying throttle problem.

Okay here's the skinny:
89 GTU converted to TII.
complete S5 jspec
full TII drivetrain
Aspec N370 ECU, pressure sensor and wiring harness, aspec BAC valve
no A/C.
I still have the ACV but I have no air pump.
The injectors are cleaned and flow-matched.
I'm still using the NA fuel pump (temporary)
N370 TII AFM (known good)
new silicon vac hoses throughout
3" TID
Greddy BOV
new O2 sensor
new fuel filter
new engine and chassis grounds
TPS set to 1Kohm with engine at normal operating temp.
using a "test-pipe" in place of an intercooler (for tuning sake)
I have been unable to find any intake leaks (using small amounts of "starter fluid" around all connections)

OK, here is the problem, when I start the car it fires on the first try everytime and I was able to tune it to a rock-solid 750rpm idle. when I accelerate, the engine accelerates silky-smooth in every gear even past the infamous "3800 rpm hesitation" zone without any problems. BUT, once I get to my desired speed, lets say 50MPH and I want to hold it at that speed, the throttle acts as if it is SUPER sensitive and it wants to buck and jerk and sort of "hesitate" until I either let off or start accelerating.

now, this happens in any gear and any speed and in many different rpm ranges, thats why I call it a "throttle problem".

has anybody had this happen to them, and does anybody have any ideas?

just FYI, I WILL be getting a higher flowing fuel pump and I have not taken the car past around 4-5K RPM, I have not been into boost higher than 2-3PSI for any more than a couple of seconds (I am way to paranoid to blow something) but I need to get this thing figured out before I get my IC and fuel pump on there.

Sorry for the length and thanks for any help,

Tony E.



"Normally I'm a pretty resourceful guy and if I really didn't need the help I wouldn't ask for it......." What movie?

 

^^

 

I gotta get this figured out, I can keep the bucking to a minimum but I'm afraid its putting a lot of strain on my drivetrain everytime it happens.....

 

Broken Front Differential Mount? Do you get a thud in the rear? I thump and jolt everytime I decellerate and accelerate shortly between one another.... I dunno just a guess.

--Fritz

 

TPS?

 

I don't have a broken diff mount, my engine is bucking and hesitating while cruising only, never during acceleration/decceleration. I need to fix this before it starts breaking stuff.

 

Thats what everybody keeps saying but I've had a bad/not setup TPS on earlier cars and this is not what it felt like.

if I'm extremely gentle with the thottle when this happens I can sometime keep it from happening.

could it have anything to do with the fact that my ACV is still installed but without an air pump?

 

maybe misadjusted thermowax? anybody know the best way to adjust that?

 

I think if you wait for the car to warm up then adjust it, I think it is in the FSM... ill have to double check

 

I'll bet you have a worn out short range TPS.

It will show 1K ohms at idle & go th ~5K as you open the throttle, but it has a dead spot in the plunger stroke just above idle.

 

D/P

 

I really hope thats not the case, I don't wanna have to get a new one...$$;(

something I noticed today, this problem seems to be a little less evident when the car is really warmed up.

any more thoughts?