QuestionMy '94 Altima seems to have an intermittent problem (or maybe more than one). It currently has 114,000 miles on it, and has only had one other owner who took very good care of it.
I've been trying to figure out what's wrong with it for about a month now but I have to have it to drive to work so I can't do a tear-down without knowing what I'm looking for.
Here are the symptoms:
1) When driving on the highway it will suddenly drop about 500 rpm. It will still accelerate from there and it will usually straighten out within 20-30 seconds. As I said, this is intermittent and will happen at 70mph just the same as at 30 or 50.
2) When at low rpm (coasting or stopped at lights/stop signs). The problem causes the car do sometimes stall and die. Sometimes it drops the rpm (to 0 momentarily) and then comes back to idle. This will happen weather I have actually driven the car anywhere or if I've just turned it over. Whenever this happens the car usually has no trouble restarting since the problem usually corrects itself when it dies. I say usually because there have been a few instances when it did not correct itself when the car died. The car can be kept running when it does this by depressing the gas pedal.
3) Today it seemed to flood the engine when it died... Twice...
4) It's using an exorbitant amount of fuel barely getting 10 mpg but doesn't seem to have any fuel leaks.
Now for what I've done so far.
Changed the fuel filter, ran cleaner through it because I thought it may be bad gas.
Then it coded camshaft position so I assumed it was a distributor problem. I got an old OEM from the junkyard, cleaned the oil out (since I know about that problem), replaced the O-rings and installed it. The distributor was good as the car in question had been running on site less than a week before I got the distributor.
This cleaned up the idle (which had recently been a bit rough) but didn't do anything for the idle/running problems.
Still thinking it was an ignition problem I changed out the plugs and plug wires since neither had been changed since I had the car.
No change
I've been through the vacuum system but haven't found any leaks (changed all the hoses regardless).
No change
Checked the EGR manually but it seems to be working fine. Regardless, I disconnected it and sealed the vacuum line for a couple days to make sure it would not adjust and had no change in the problem. I'm probably going to pull it and clean it out just for good measure since I already got the gasket
I've started checking sensors now but the only thing coding is the Knock sensor which would effect my fuel economy a bit but shouldn't have that significant an impact on fuel consumption.
I was thinking about changing the PCV valve while I was doing the knock since I have oil leaking out beneath the distributor which I've read can come from increased crankcase pressure but I don't' know that this will have any impact on the problem I'm having.
Sprayed the intake gaskets with carb cleaner to check for a leak but didn't find anything.
So far:
MAF is good.
Throttle position is good
Any help in pointing me in the right direction would be great.
Thank you Very much
Chris
AnswerChris,
The knock sensor is vital to engine management since it keeps the car from knocking the rods out of the engine. If the computer reads the knock sensor as defective the computer will retard timing to protect the engine. Replace the knock sensor.
