Bucking when I hit the throttle?

[Brian685]

Recently when I get on the gas in 1st or 2nd gear the car starts bucking violently and the tires start chirping and I can't seem to figure out why.

I DO know that my throttle cable and cruise cable got messed up so I disconnected the cruise for now... but one of the brackets was somewhat bent.

Is this a TPS problem? A throttle cable problem? Early signs of CPS? Anything would help. Thanks.

- Brian

 

[Huntervf]

The CPS won't yield symptoms like the ones you're describing. Nor would a goofy cable cause this. Do you have a CE light? Tried pulling any codes? I can think of a few different problems that could cause this...TPS is a possiblity...try pulling codes and see what you get.

 

[naval-avi8or]

Please let us know if it is a ATX or MTX. If its an ATX it may be the first and last sign of bad news.

Also check your plugs and wires and for oil in the plug wells.

 

[AutoSHO]

My old 93 ATX had the same problem, and we replaced the MAF sensor + the TPS sensor, problem solved. Not sure which it was, but its pretty much free to clean the MAF and that is an easy task. Do you have a K&N in the car? Has it been cleaned lately? Good luck!

 

[AutoSHO]

naval-avi8or:
Please let us know if it is a ATX or MTX. If its an ATX it may be the first and last sign of bad news.

well, its an 89, so I assume its an ATX. As for failing, I doubt that a transmission would do that, as usually the clutches just start to slip between shifts, not while in gear accelerating normally.

 

[sho_dwn]

89-92 only came with a 5-speed. My 89 had similar symptoms and it was the computer itself. Is your Check Engine light on? If it is you might want to check the computer out if you know someone you can swap with. If the CE light isn't on, then it is a secondary problem as it is not throwing codes at you.

 

[luigisho]

Have you checked for codes? See what comes up. Check plug wells for moisture. I would next take the cheap route of cleaning the MAF and the IAB. The TPS is a cheap part to replace also.

Isn't bucking also a sign of cam sensor failure?

<small>[ May 27, 2002, 11:26 AM: Message edited by: luigisho ]</small>

 

[naval-avi8or]

Hey guys I don't ever assum its the car in the sig. to many of you guys have several or are helping other shos. So please always put what your working on.

As far as the tranny thing it just happens to be what my 94 ATX did when it ate all the gears including the planitary.

What luigisho said is a high possibility if the CID starts to fail.

<small>[ May 27, 2002, 01:10 PM: Message edited by: naval-avi8or ]</small>

 

[Brian685]

I will pull the codes in a bit. But some background info: I do not have a K&N, or aftermarket MAF... I will look for the CE light. The bucking feels like somebody is stabbing the throttle, then letting off and slamming the brakes, then another throttle stab... which caused the tires to chirp while accelerating, then decelerating. It's scary. What should I start with?

- Brian

 

[luigisho]

Start with checking the plug wells for oil in them. Next see if any codes are stored in memory. If present they are a great way to help diagnose problems (that's what they're for). To see if it is the maf you can run it with the connector unplugged. If it stops the symptoms then the MAF is the problem. Then you can replace the TPS. How about fuel filter? Does it have these symptoms at idle also or just with throttle? CID still comes to mind here.

 

[Brian685]

These symptoms have only come up when I get on the gas and look for a little fun... at idle and lower levels of throttle I get nothing. At least not yet I haven't.

- Brian

 

[Brian685]

Not a drop of oil in the plug wells. Some good news considering I have 100k miles! Right now I'm going to go pull the codes, and check the MAF by running w/out it connected. I'll check back with results.

- Brian

 

[snake396]

how many miles are on your plug wires? mine did the same bloody thing. 207k on them, replaced with a set that had only 100k on them. bought them for only $20, problem solved.

-Ian

 

[Brian685]

Unplugged the MAF, no changes... still bucks at full throttle. Will have codes in a minute.

 

[Brian685]

Ok I did the key on engine off test and got the following codes

First set (on demand): 15
Stored codes: 18, 66

15 is an ECA ROM Failure, 66 is a low voltage from the MAF... but 18 isn't even listed for KOEO test??? My blinks went as followed

1 blink, 5 blinks / 1 blink 5 blinks

1 blink

1 blink 8 blinks / 6 blinks 6 blinks / 1 blink 8 blinks / 6 blinks 6 blinks.

Please tell me I read the codes properly? Thanks.

- Brian

 

[brianl]

OK, try this-

Does it accelerate OK if you 'squeeze' the throttle instead of mashing it? Mine does this (90 MTX), but generally only when you mash the throttle open at lower gears/RPM's. I assumed it was something in the fuel delivery (pump, injectors, etc). My car has always done it, it's just getting worse now, and it seems worse when it's low on gas (fuel pump...). I'm in no rush to do anything about it right now as I have another one in the garage . It's worst in the lower gears, and almost never happens at highway speeds. The reason it's so violent is that you mat it, the car starts to lunge forward, then it dies for a second, if you're in first gear, you get heavy engine braking, it will lock my belt, then it comes back to life, chirping the tires. I always let off at this point and it's fine.

It seems I've been hunting for this gremlin for awhile, so the bad computer suggestion seems good too. Hmmm, maybe I'll pull the computer out of the SHO in the garage and put it in the 'current' one...

 

[luigisho]

Well, I'm wondering if the MAF code was thrown because you ran with it unplugged before you pulled them. ROM failure doesn't sound good. Avi8tor is the tech manual man here. I would try a new tps. The plug wire mentioned sounds interesting. Now the best way to narrow the possibilities is if you can find a SHO owner from here that's not too far. Then you can just take and hour or so and swap stuff out so you don't spend tons of money on new parts (like swapping the pcm). I'll look for the code meanings and check back. I think sometimes the cam sensor doesn't set off codes when it's failing.

 

[BigSHO43213]

My '91 SHO Had the same problem and I replaced the tps, and the Bap sensor and that took care of the problem and I've got 145k miles

 

[Brian685]

The problem happens whether I squeeze or mash... as long as I reach full throttle somehow it starts bucking. It also seems to happen around when the secondaries open. I can't be sure but the last instance definitely did.

- Brian

 

[naval-avi8or]

Try using a little less throttle until it doesn't do it anymore, or just test your TPS possible tps going out of limits. Some members have had some luck with adjusting the tps. I couldn't see any adjustment slots on mine. But a little twist and retighten could go along way. So loosen the tps screws and see if it will twist a little counter clockwise and retighten. So if it helps if not test or replace.

As luigisho if you pulled the codes after you ran the motor with the MAF unplugged thats what poped the MAF code.