What would you guess this problem with my car is? ;)

[StageLeft]

Gonna likely take it into a mechanic but it's difficult to explain so I may need to point him in the right direction in case I can't replicate the problem.

93 sentra with 5 speed: sometimes when I'm at lights I get a very quick shudder for a split second. It's like the revs drop too low and then the engine speeds up to normal idle again. This happens in gear with clutch in or out of gear in neutral as well.

Tied in with this is sometimes I'll be accelerating and I get multiple shudders at once (as opposed to the single shudder at lights). These generally are only at low RPM when accelerating and if the RPM are higher I don't get these. The best way to explain these would be if you were accelerating and you let off on the gas really quickly and then pressed it on, then off really quickly then on again although their interval is far too short for a person to replicate doing what I just said, but that's the best way to explain it.

Without knowing anything else what would this situation likely be caused by?

TIA!

EDIT: Something that MAY be related that I just thought of is since I bought the car 13k miles ago sometimes when I'm in 4th gear and accelerating I get a weird thing. Basically it's like this: 20% throttle = 20% acceleration, 40 = 40, 50=50, etc. However, when at perhaps 70% throttle I get a dip down to 35% acceleration - it's like at one particular part of the pedla down the engine only works at half power, so if I avoid that part of the pedal down (either less or more) I don't have that issue at all.

In regards to tominator's question the idle does change when AC is turned on but I can't remember if it's up or down.

ALSO is it bad to leave a problem like this...?

 

[splice]

Is it pretty hot and dry where you are? Sounds like vapor lock to me, usually caused by gas that has a higher percent of alcohol. This use to happen a lot with my old Mazda B2000 truck.

 

[The Stigenator]

if its a fuel injected car it could be something in the ignition (sparking portion of it) / fuel injection portion.

My car used to do that before it died.

They replaced a heck lot of things and turned out they still got it wrong.

Try raising the idle speed that should hold it off .... next set of problems would be a stall when the rpm's dip and then the whole thing starts like mine did.

 

[StageLeft]

Originally posted by: splice
Is it pretty hot and dry where you are? Sounds like vapor lock to me, usually caused by gas that has a higher percent of alcohol. This use to happen a lot with my old Mazda B2000 truck.

how is this fixed...?

Try raising the idle speed that should hold it off .... next set of problems would be a stall when the rpm's dip and then the whole thing starts like mine did.

I could certainly see that helping for the issue at the lights but how would that help when I'm accelerating since it seems kind of impossible for the car to stall at that point if I have enough gas going to it...?

 

[The Stigenator]

Originally posted by: Skoorb

Originally posted by: splice
Is it pretty hot and dry where you are? Sounds like vapor lock to me, usually caused by gas that has a higher percent of alcohol. This use to happen a lot with my old Mazda B2000 truck.

how is this fixed...?

Try raising the idle speed that should hold it off .... next set of problems would be a stall when the rpm's dip and then the whole thing starts like mine did.

I could certainly see that helping for the issue at the lights but how would that help when I'm accelerating since it seems kind of impossible for the car to stall at that point if I have enough gas going to it...?

my car used to shudder when acclerating.. it was like it was running too lean.. the condition is a lean burn condition.. raising the idle solves the problem.

 

[gogeeta13]

i have had that problem before, it was resolved with new spark plugs and wires, the engine was mis-fireing

 

[The Stigenator]

Originally posted by: gogeeta13
i have had that problem before, it was resolved with new spark plugs and wires, the engine was mis-fireing

if its a lean burn condition the spark plugs should show it to an idling engine.

 

[StageLeft]

If it is the spark plugs is it bad if I leave it in this condition? I mean it's annoying but I don't really care about it. I thought it had to be engine or transmission and since it does it out of gear as well when at lights I figured it must be engine...

 

[lepper boy]

my advice is before you go about replacing spark plugs and adjusting idle. I would Go by a new gas filter and put it in.... had a car that had same problem, talked with my dad he says change the fuel filter, changed it problem was fixed.......

dave

 

[Muadib]

MY gf's Altima does this too. She's taken it to the dealer about 10 times for it, but they never find anything.

 

[Kadarin]

Hard to say for sure, but I'd replace the fuel filter first, then try distributor cap, plugs, and plug wires next if the filter doesn't solve the issue. Check also to make sure the air filter's not totally black with gunk..

 

[Muadib]

Originally posted by: Astaroth33
Hard to say for sure, but I'd replace the fuel filter first, then try distributor cap, plugs, and plug wires next if the filter doesn't solve the issue. Check also to make sure the air filter's not totally black with gunk..

Would you let jiffy lube change a fuel filter?

 

[Tominator]

If the car has an air conditioner does the idle drop a bit when the compressor kicks in?

Sounds like the throttle body idle motor. The part is called by various names depending on the manfacturer but it adjusts the idle.

If it is a fuel injected car there is no idle adjustment. Yes, there is a little stop screw but it is to fine tune the linkage and will not help if a part is malfunctioning.

Usually the part is on the bottom of the mass air sensor and has two little water hoses attached as well as an electrical plug.

 

[Kadarin]

Originally posted by: Muadib

Originally posted by: Astaroth33
Hard to say for sure, but I'd replace the fuel filter first, then try distributor cap, plugs, and plug wires next if the filter doesn't solve the issue. Check also to make sure the air filter's not totally black with gunk..

Would you let jiffy lube change a fuel filter?

Come to think of it, I'm not sure I have faith in Jiffy Lube changing an oil filter...

(and I take my car there..)

 

[Bluefront]

93 Sentras are fuel-injected. Assuming the tune-up parts are good, fliters, plugs, plug wires, etc., it sounds like an EGR problem, maybe sticking. That could affect the idle, as well as low speed acell....and would go away on heavy acell.

Sentras of that year had some distributor (crank angle sensor) issues....but they only showed up under very hot conditions, ran ok cool. And when they started failing, the problem was there all the time.

The idle speed motor (AAC valve) could give you similar symptoms, but you probably wouldn't notice them on accell. Time for a good dealer to step in.....

 

[IGBT]

Throttle position sensor..mabe. Located on the FI throttle body...

 

[StageLeft]

updated first post!

 

[Bluefront]

Your updated info may point to a throttle position sensor...but that's a pretty rare failure on this car. I doubt if this situation would cause any further damage. Once it becomes more frequent, or completely fails, it should be much easier to pinpoint.

One more thing....an intermittent failure of one injector might cause these symptoms. Not an uncommon problem.

 

[Ornery]

Damn, doesn't it suck when you can't even determine if it's electrical or fuel related? The one suggestion I liked was gogeeta13's, do a complete tune up as far as new quality wires, cap and plugs goes. Get ALL filters replaced and maybe even replace the cheaper sending units while you're at it. Do as much as you can on your own. It's all maintenance that has to be performed anyway, so no wasted dollars there. Then, if the problem persists, take it to somebody with the proper equipment to diagnose it. It's pretty disconcerting to hear that a dealer can't find a problem after several tries. Perhaps a performance shop would have better equipment and mechanics. It would be nice to put it on a dynamometer while it's hooked up to the test equipment.

 

[StageLeft]

UpdATe: Well I took it in yesterday and the guy said the plugs were nearly blown. I had them, the wires, the air, and fuel filter all replaced. He said the fuel filter was nearly totally clogged. Whatever the overall problem was one of these things fixed it. the car has no problem now and this actually steadied up something that I used to think was transmission and had to endure for many months. Car is much much nicer now

 

[iamwiz82]

it was probably a combination of fuel filter and spark plugs. Don't you check these things?

 

[jemcam]

Originally posted by: Muadib
MY gf's Altima does this too. She's taken it to the dealer about 10 times for it, but they never find anything.

It sounds like it's the A/C compressor kicking in & out. It's much more noticeable on smaller cars w/smaller 4 cyl. engines. It normally cycles to keep the evaporator core from freezing into a solid block of ice. The A/C compressor also kicks off when you get close to wide open throttle. You feel it cycle at a light because there is less vibration in the car because it's not moving.

 

[Muadib]

Originally posted by: jemcam

Originally posted by: Muadib
MY gf's Altima does this too. She's taken it to the dealer about 10 times for it, but they never find anything.

It sounds like it's the A/C compressor kicking in & out. It's much more noticeable on smaller cars w/smaller 4 cyl. engines. It normally cycles to keep the evaporator core from freezing into a solid block of ice. The A/C compressor also kicks off when you get close to wide open throttle. You feel it cycle at a light because there is less vibration in the car because it's not moving.

No, it still does it with the AC off. I think I'm going to have her do what Skoorb did, and get a tune up.