98 Cavalier - intermitent engine shudder

Blind_Io

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A friend of mine has a 98 Cavalier he inherited and it's the most expensive free car in the world. This POS is a hole to pour money into and he can't get ahead of the repairs to save up for another car. Recently he has replaced the fuel filter, air filter, and battery.

Now the car has started to shudder when he stops on this steep hill, the oil and battery light come on (probably due to low engine RPM). If he turns it off and back on again, the car is fine. The most recent occurrence was after a hard stop. Fuel level doesn't seem to matter, he says it does it with a full tank or a quarter tank (I was thinking low fuel or low fuel pressure).

Any ideas? I'm thinking something electrical that is affecting the spark or the ECU is faulty.
 

GRtak

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It is 20 years old and should have been put out to pasture already.

I see the fuel and air filter as normal maintenance, was the battery old, or was it having starting problems?
 

Blind_Io

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I'm not sure on that, he may have replaced it because the battery light was coming on when it was shuddering or it was just old and needed to be replaced recently. I know it's a POS car, but it's literally the only transportation they have and he needs a car to get to work. I was thinking it might be a vacuum leak or EGR problem, but that doesn't explain why the car would be fine after turning it off and back on again.
 

GRtak

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This could be an electrical gremlin. It could also be the idle speed control, dirty fuel injectors, or vacuum leaks. It is really hard to tell with so little information.

Do you have a OBD2 scanner?
 

73GMCSprint

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I wouldn't yet rule out the fuel pump. Could also be fuel pressure regulator or dirty/bad MAF sensor. Did he happen to replace the air filter with an oiled filter (like a K&N)? If so it's probably a dirty MAF from the oil.
 

Eye-Q

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Yeah, could be a host of reasons, for example a faulty sensor. I had that in my old 320i, there it was the crank position sensor. When I turned it off and on again it was fine for a short time, then the same symptoms came back up again.

In 98 there should be an OBD connector already so take an OBD scanner (or go to a garage to scan it) and see if there is any fault stored.
 

Blind_Io

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73GMCSprint;n3551030 said:
I wouldn't yet rule out the fuel pump. Could also be fuel pressure regulator or dirty/bad MAF sensor. Did he happen to replace the air filter with an oiled filter (like a K&N)? If so it's probably a dirty MAF from the oil.
I doubt he would have the money to buy an expensive oiled filter, plus, he's not the type to try to "upgrade" parts.
 

Blind_Io

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Eye-Q;n3551031 said:
Yeah, could be a host of reasons, for example a faulty sensor. I had that in my old 320i, there it was the crank position sensor. When I turned it off and on again it was fine for a short time, then the same symptoms came back up again.

In 98 there should be an OBD connector already so take an OBD scanner (or go to a garage to scan it) and see if there is any fault stored.
I bought him a code reader a while ago, he says the only fault is a P0440 or P0442 (can't remember which one right now).
 

CraigB

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Being able to read fuel pressure when it does one of these episodes would be a great help. Do the Cavaliers have a Schrader valve where a cheap fuel pressure gauge could be teed in for awhile?
 

Blind_Io

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I honestly don't know, he's in San Diego so I can't physically inspect the car.

Another option I'm considering is trying to get him into a surplus Panther platform, he has about $1,200 put aside right now which might be enough to get a 100K miles or so at auction.
 
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