Combination of driveability issues. Doesn't make sense..

281pony

281pony

Active Member
Aug 31, 2003
2,681
2
46
Oly, WA
#1
not sure how to begin here, it does several things.

my biggest issue is when i am driving at cruising speed, very light throttle application it starts bucking violently. i unplugged my iac, no help. next i tried my tps sensor, which was just set/seemed to transition voltage smoothly.

for roughly 10 minutes of driving, it drove MUCH better. i could almost let it idle in gear and it would just chug along with very minimal feedback. no major bucking, ect. then it started doing it again. this entire time the car was fully warm.

however, this did completely cure another issue i had. when rolling at any speed over 5mph, push in clutch and rpms hung at 1200-1300. then as you were nearly stopped 5 mph and under, they would rise to 1500 rpm and hang for a second, then drop back to idle. with the tps unplugged, the idle dropped instantly to idle. i did throw a check engine light, but the idle works.

i am getting 41 and 91 for both o2 sensors. could the tps have any correlation to the o2's? i looked this engine over before for vac leaks when it was surging with no luck finding anything. this is one of those gremlin's that is driving me INSANE.

what do you guys think? replace tps and go from there? should i try to drive it with o2's unplugged? i haven't had much time lately to jack it up and unplug those yet.
 

  • Sponsors (?)


#2
the only other "issue" with the car, i don't believe there is any relation...

the lights in the car have a shimmer effect to them at idle. they kinda flicker/dance like a candle does. it has a 3g alt with upgraded wiring. i also have dual 4g ground wires from the left/right sides of the block, to each upper sway bar bolts. the surface was ground clean of paint prior to torquing the nuts down.

once i can trace this bs issue, i'm scheduling an immidiate dyno tune appointment. perhaps this is just a tuning issue at this point? :shrug:
 
#3
How old are you spark plug wires? Jerky performance under light acceleration and lower RPM cruising can sometimes be attributed to an ignition issue.

Try cleaning out your IAC for the hanging idle issue. These baby's carbon up over time and one moment cause a sticky high idle and the next they won't idle at all. You could test the TPS with a volt meter to see if the voltage increase is constant or if its jumping erratically all over the place. That would be an indication that its bad....and if the O2 sensors have a lot of mileage on them, it wouldn't hurt to change them either.

Have you underdrive pulleys on the car, or a big stereo or something that's creating excessive electrical load? How about a lumpy cam or low idle that might cause charging issues? If the lights are only flickering at idle, you could always bump it up a couple hundred RPM and if that doesn't work, look into picking up a slightly smaller alternator pulley to speed things up at lower engine RPM.

I was having this issue as well with my F150 after installing underdive pulleys (it's got a 6G alt), but after a pulley swap to a smaller diameter alt pulley, the problem was solved.
 
#4
i didnt want to type a book, cause most people overlook long threads. however;

-brand new, safely routed taylor 409 wires.
-cleaned the piss out of the iac. its clean as its gettin. i even used a q-tip.
-tps was just set, smooth voltage transition clear to wot. i was using a digital display though, not a needle style. it SEEMED good.. but im sure its difficult to tell with those.
-unknown mileage on the o2's. was hoping to replace them only if necessary, can't really afford the $100 for a pair of bosches for chits and giggles.

it does have underdrive pulleys AND i guess a big system? i'm running 2 amps and 1000 rms watts. it does this with no stereo on though also. i can and will try a smaller alt pulley if that could be the issue. where do you order them?

its a tfs stage 1 camshaft. its set at 950 rpm, on the high side so it doesn't lope much at all.
 
#5
Just a some suggestions? Maybe clean the MAF itself? Charging system i've asked about the same thing and was told to go to stock crank pulley and an OVERdrive alt pulley.You say your gonna dyno that thing? If you can and if john is cool with it witch i'm sure he will be.After you get the car tuned the best he can,see if he will let you make a pull with under drive pulleys and another pull with stock ones?I'm really curious and wanting to see someones TRUE results,instead of relying on the mags and car program's BS.peace












john:p
 
#6
281pony said:
not sure how to begin here, it does several things.

my biggest issue is when i am driving at cruising speed, very light throttle application it starts bucking violently.

when rolling at any speed over 5mph, push in clutch and rpms hung at 1200-1300. then as you were nearly stopped 5 mph and under, they would rise to 1500 rpm and hang for a second, then drop back to idle. with the tps unplugged, the idle dropped instantly to idle. i did throw a check engine light, but the idle works.
Click to expand...

mine does both of these. i always thought the bucking was because i wasnt going fast enough for the gear bc if i downshift, it drives fine or if i give it throttle, it drives fine until i let it idel and it slows down again.

also my rpms also take a second to drop when i push the clutch in or put it in nuetral to let it glide towards a stop or whatever. then when im almost at a complete stop, the rpms drop to idel rpms. sometimes they surge though.
 
#7
To cure the bucking, try backing off on the timing a degree or two. That can often be the culprit at low RPM

...I'll have to look around for the place that I found my new alternator pulley at and get back to you. :)
 
#8
i did some more testing..

timing is at 12* already, i'm going to set it at 14* this weekend actually. i run premium as it is, might as well try it.

unplugging my tps, cured the hanging idle coming to a slow/stop.

it also, temporarly (10 min) cured the bucking in gear. so i am replacing the tps today and i'll go from there.

i might just smile and bend over, and replace the o2's anyways. i have no knowledge of how old they are.
 
#13
You say you've got new wires....but how old are the plugs and what are they gapped at?

It probably won’t make a difference, since you’ve got aftermarket wires, but make sure #7 & #8 plug wires are separated and not running parallel to one and other. It’s been known to cause a miss with the HO firing order in the past.
 
#16
so i put on my new tps, and i'm pissed to say the least.

i set the voltage, start the car. it started, and was surging up and down from 1000-1700. it was almost like it was a controlled rev though. it wasn't nasty surging that causes the voltage meter to fluctuate. it was just revving from 1000-1700.

so then, i hit my battery cutoff and let it sit for 15 minutes.

start it again, and now it just "settles" to 1500 rpm's. i kept letting clutch out slowly and letting it pull the rpm's down, then pushing the clutch back in. rpm's would just transition back up to 1500 and sit there.

so wtf now? this acts completely different over my old tps, it still DID surge like the old one at start up. now it just hangs instead of settling rpm's though. :mad::mad::mad::mad:
 
#17
ok, i played with my idle screw and let it reset.

i turned the idle down until it would just die on startup then slowly came up higher. i got it to idle at 850 rpm. i let it idle and get hot.

i can let the clutch out using no throttle and it will hold a good idle and no surging.

on hot starts, it surges bad. from 500-1500, if i tap the throttle i can somewhat get control over it. eventually it stops surging less and less, from 1000 rpm increments, to 500 rpm increments, to 250 rpm increments, to a steady idle.

if i rev the car in neutral, it doesn't just settle. it will surge lightly, roughly 300 rpm range of surging. it settles back to a steady idle on its own after like 10 seconds.

so this surging deal, my iac is CLEAN. should i just replace it completely? i'm so tired of chasing this crap, i think i have a nasty flu coming. i feel like chit so i just want this to go away.
 
#18
I still think the problem may lie in you IAC. You said you cleaned it, but if its original, it may be beyond just a cleaning. That diaphragm inside are after all sealed with rubber. It may over the years have dry rotted, or sprung a small leak or plain and simply just wore out?

...also, to truly clear your computer, you need to pull the battery cables off and touch them together for a couple of seconds to discharge the stored energy. Just removing the power from them won't completely do it.
 
#19
Gearbanger 101 said:
I still think the problem may lie in you IAC. You said you cleaned it, but if its original, it may be beyond just a cleaning. That diaphragm inside are after all sealed with rubber. It may over the years have dry rotted, or sprung a small leak or plain and simply just wore out?

...also, to truly clear your computer, you need to pull the battery cables off and touch them together for a couple of seconds to discharge the stored energy. Just removing the power from them won't completely do it.
Click to expand...

ok, ill try touching them together. ive also tried 2 different iac valves and they both had the same results. granted, neither were new.
 
You must log in or register to reply here.

Similar threads

Vulpes5.0
Car idles good, then VERY SUDDENLY dies
Replies
25
Views
2K
Fox 5.0 Mustang Tech
Vulpes5.0
Vulpes5.0
LILCBRA
I feel like I'm chasing my tail with this thing
Replies
36
Views
3K
Other Auto Tech
LILCBRA
LILCBRA
W
Resolved Loss of Horsepower After Base Idle Reset??
Replies
8
Views
1K
Fox 5.0 Mustang Tech
WTW
W
B
94 cobra possible idle issue?
Replies
11
Views
681
1994 - 1995 Specific Tech
Noobz347
Noobz347
K
95 GT Issues and Codes - 158, 172, 176, 212
Replies
13
Views
1K
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
manicmechanic007
manicmechanic007
Top Bottom
Back
New
Hot
Menu