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Dreaded P0340 Code

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Guys, I am getting the dreaded P0340 code. My car (96-ls400) would start and then the RPMS would go to 2000 then 1000 back and forth several times and after few seconds it will die. same thing when I restart.

If i give throttle, the engine will not die but The car shudders and the rpms still keep on going up and down. eventually if I let the throttle down the engine will die.

Here is what I have done till now.

a) traced wires for shorts. They checked out ok.

B) Tested resistances for both camshaft sensors and the crankshaft sensor, all came out to be within the right specs.

c) tested ignition coil resistances, came out to be within the right specs.

Do you think my timing is off?.

My car was running perfectly, this only started with the below 20F tempratures we are getting in Florida. do you guys still think it is the sensors going haywire because of the cold?

Help definately needed from the gurus out there. Please Help. Thank's!!!!!! :)

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Guys, I am getting the dreaded P0340 code. My car (96-ls400) would start and then the RPMS would go to 2000 then 1000 back and forth several times and after few seconds it will die. same thing when I restart.

If i give throttle, the engine will not die but The car shudders and the rpms still keep on going up and down. eventually if I let the throttle down the engine will die.

Here is what I have done till now.

a) traced wires for shorts. They checked out ok.

B) Tested resistances for both camshaft sensors and the crankshaft sensor, all came out to be within the right specs.

c) tested ignition coil resistances, came out to be within the right specs.

Do you think my timing is off?.

My car was running perfectly, this only started with the below 20F tempratures we are getting in Florida. do you guys still think it is the sensors going haywire because of the cold?

Help definately needed from the gurus out there. Please Help. Thank's!!!!!! :)

Suspect a faulty sensor, they're usually the culprit when wiring, etc. has been eliminated.

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i have a similar problem when it is very cold outside (i live in jacksonville very cold in fl this year) whenever my car starts it's air to fuel ratio is off. it misfires extremely bad and i cant really drive it until it warms up or else i'll have to drive it extremely slow. i'm going to replace my maf soon and see if that helps. Good luck on your problem

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The fuel is cut at 2k rpm's when the TPS sensor idle position. The ECM will not let the "idle" above 2k. It will bounce because the fuel is cut at 2k and reintroduced at a lower rpm. My '96 did this as well as a very high idle when it wasn't doing this. Have you ruled out your Idle Air Control Valve? They're known to cause some issues. You can tell if it's actuating without removing the sucker by having someone sit in the car and start it then shut it off. With your head near the IACV you'll hear it click back to the open position. If you hear no clicking it may be jammed, it's not very loud. IACV's are VERY expensive. I had this same problem and my IACV was fine. I removed it and it actuated per the book. Funny thing is, my factory manual's do not show a troubleshoot procedue for P0340 in the engine diagnostics section...

Do you have any friends with repair shops with scanners that can read real-time sensor data? The idle is decided by several things including ECT (Engine Coolant Temperature.) Unplug your ECT sensor. It is green in color and located under your plug wire bridge. You may have to losen your pass. side timing belt/plug wire cover to get some room to lift the bridge up a little. When you unplug your ECT the ECM assumes the engine temp is 176*F. It should cold start really really bad but run good when it's warmed up. It's going to be tough trying this in the cold weather, may have to wait until it warms up. a little. The ECT sensor is a good one to replace if the car is high miles and has the original sensor. It really controls alot. Alot of owners have reported better gas mileage with new sensors as well because with a sensor that reads cold the car thinks it's not warming up and continues to run rich.

How many miles are on your car? My '96 had an enormous amount of general running conditions including: Super high idle, sometimes super low idle, very rich running, hard to hot start, floods easily, smells like rotten eggs out of the exhaust, P0115 ECT circuit manfunction codes, poor power and bad gas mileage to name a few. All of these were caused by a bad ECM. I replaced the ECM with a good low miles unit for a couple hundred bucks and it's like a new car. Every problem it had running wise is gone and it runs like a sewing machine. I know you may hate to hear that your ECM may be bad but there are options. In the factory manuals, if all checks of sensors associated with a certain code are checked good then the last step is usually to replace the ECM. The ECM can be throwing a code that it's causing while the circuit/sensor is operating just fine. With mine, the source voltage was running really high on the ECT circuit and made the ECM thing the car was very cold no matter what when the sensor and circuit had good info going INTO the ECM. Yet it threw a code saying there is a problem with the sensor or circuit. Don't be fooled very easily. The 94 and 96 ECM's are known to go bad with mileage/age. Don't suspect the worst but it is a possibility. If, in fact, your ECM is found to be the problem there are a couple of shops that fix circuits for around $400. If you are lucky enough to find a ECM that matches your model year like I did that will be your best bet.

-Kelly

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Hi Guys,

Banshee365 Thanks for your excellent feedback.

Here is the complete story. My LS has been working perfect since last year, no complains, . I was parking at the local walmart with tempratures down to 16F. Suddenly it starts acting up and showing the symptoms above. I was able to limp it back home, after that the rpms would never stabilize the car would die in a few secs after starting.

I had a issue during last years winter when the car would start and blow out white smoke. everybody had said it was a shot gasket but it turned out to be a bad ECU. when we opened the ECU we saw acid eating up parts of the circuit and knew there and then, that it was an issue. Changed ECU and the car chirped like a bird!!! as i said it was perfect till that fatefull day at Walmart!!.

I could never get to test the car at higher temps, because currently the highest temp here in tallahassee is 40F (in Florida, can you believe that!!!)

I am pretty sure the cold weather is the cluprit, since I am not getting any feasable resultsby testing sensor specs, I am going to try something else. will start by taking a small handy heater and directly heating the sensors in the following manner.

a) ignitions coils

B) camshaft sensors

c) crankshaft sensor

d) IAC.

e) eventually if I dont get any concrete results I will have a bigger heater to heat the

whole engine and see the results.

I am betting that it is going to be one of them. I have ordered a,b and c sensors,

i want to replace them anyways as preventative maintainence.

I am excited and have a long day ahead of me, I will update results.

Wish me luck Guys, Again Thanks for all your inputs

The fuel is cut at 2k rpm's when the TPS sensor idle position. The ECM will not let the "idle" above 2k. It will bounce because the fuel is cut at 2k and reintroduced at a lower rpm. My '96 did this as well as a very high idle when it wasn't doing this. Have you ruled out your Idle Air Control Valve? They're known to cause some issues. You can tell if it's actuating without removing the sucker by having someone sit in the car and start it then shut it off. With your head near the IACV you'll hear it click back to the open position. If you hear no clicking it may be jammed, it's not very loud. IACV's are VERY expensive. I had this same problem and my IACV was fine. I removed it and it actuated per the book. Funny thing is, my factory manual's do not show a troubleshoot procedue for P0340 in the engine diagnostics section...

Do you have any friends with repair shops with scanners that can read real-time sensor data? The idle is decided by several things including ECT (Engine Coolant Temperature.) Unplug your ECT sensor. It is green in color and located under your plug wire bridge. You may have to losen your pass. side timing belt/plug wire cover to get some room to lift the bridge up a little. When you unplug your ECT the ECM assumes the engine temp is 176*F. It should cold start really really bad but run good when it's warmed up. It's going to be tough trying this in the cold weather, may have to wait until it warms up. a little. The ECT sensor is a good one to replace if the car is high miles and has the original sensor. It really controls alot. Alot of owners have reported better gas mileage with new sensors as well because with a sensor that reads cold the car thinks it's not warming up and continues to run rich.

How many miles are on your car? My '96 had an enormous amount of general running conditions including: Super high idle, sometimes super low idle, very rich running, hard to hot start, floods easily, smells like rotten eggs out of the exhaust, P0115 ECT circuit manfunction codes, poor power and bad gas mileage to name a few. All of these were caused by a bad ECM. I replaced the ECM with a good low miles unit for a couple hundred bucks and it's like a new car. Every problem it had running wise is gone and it runs like a sewing machine. I know you may hate to hear that your ECM may be bad but there are options. In the factory manuals, if all checks of sensors associated with a certain code are checked good then the last step is usually to replace the ECM. The ECM can be throwing a code that it's causing while the circuit/sensor is operating just fine. With mine, the source voltage was running really high on the ECT circuit and made the ECM thing the car was very cold no matter what when the sensor and circuit had good info going INTO the ECM. Yet it threw a code saying there is a problem with the sensor or circuit. Don't be fooled very easily. The 94 and 96 ECM's are known to go bad with mileage/age. Don't suspect the worst but it is a possibility. If, in fact, your ECM is found to be the problem there are a couple of shops that fix circuits for around $400. If you are lucky enough to find a ECM that matches your model year like I did that will be your best bet.

-Kelly

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So you've already changed the ECT sensor? I'd do that way before the coil. I don't see the coil being an issue if it's running at all, but maybe, who knows. They're known to be pretty stout. You may have some luck with the b and c sensors but they're not known to cause many problems on these cars.

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ok guys i am back, here is what I managed to do today

a) Heated car so that it could start up without dying

car would run very bad with shaking, but idle (RPMS) got stable and it didn't shutdown. If I up the throttle, car would die.

I got P0340 now with "TRAC" light on and Off and sometimes (intermittently) p0300 (misfiring all cylinders) code.while idling.

b.) Tried a couple of things, Cleared codes before starting and

1) Since I had this flashing "TRAC" symptoms before (it was due to a bad alternator), at that time too the car ran like crap on a cue I removed the alternator and took it for a test to the nearby auto shop. alternator checked fine.

2) From my ordered parts (i had ordered two ignition coils. Two CAM sensors and one CRANK sensor), The auto shop received the

IGNITION coils today, CRANK and CAM are scheduled delivery on the 12th. I collected the coils and installed them. BUMMER didnt solve

my Issue.

3) Cleared codes before starting and disconnected CAM sensor, Driver side (bank 1)

Lo and Behold, Car stabilizes, there is occasional jitter but RPM is stable, I can now raise throttle without stalling or hesitation, idled car like this for about 5 min didnt shutdown. No sudden jerking or RPM changes. I was surprised!!! Shutdown Car and Went to next step.

NOW I am still lost why #3 would not send out any code!!!!. should detect BANK1 being disconnected!!!.

4) Cleared codes before starting and Reconnected CAM Sensor (BANK 1) and Disconnected CAM sensor (BANK2)

Car acted Like before, running bad, shaking, Idle ok. got the P0340 code.

5) smelled a rat in the CAM position sensor 1.

Just remembered I had taken the resistances for the sensors while cold. Now since the car was hot i decided to take them again. Guess what, BANK 2 stabilizes at a certain resistance while BANK1 keeps on fluctuating which was weird.

I then decided to test the voltages out of these sensors, since they generate ac voltages, These can be measured.

the minimum my meter could go down was 200V and the voltages generated by the CAM sensors are very small ~ 1-10V pulses.

I still decided to proceed, the meter was registering the voltages as in 0.001V or equal to 1v.

Here are the results of my test

BANK2 -- 1v-2v-3v-2v-1v-2v-3v-2v-1v-2v-3v ( Could make out this was cycling)

BANK1 -- 1v-1v-1v-2v-3v-2v-2v-1v-3v-3v-2v (this output looks like bad cycle, it was intermittently sending out same voltage instead of changed voltage)

looks like CAM sensor BANK 1 is a goner

I Cant verify this voltage test results with anything standard though, this is all guess work till now.

Will be waiting for my sensors to arrive and change CAM1 to verify my theory. I will let you'll know how it goes.

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Ok guys, Changed the camshaft sensor with a new one, Didnt help, same issue.

When I plug in the bank1 Cam sensor the car will not start at all. I can still make it rev by giving some more gas but it runs terrible, with bad gas smell and shaking and vibration. It will die as soon as I cut the gas. Once I disconnect the Bank1 sensor the car still runs bad (its not terrible, some vibrations) but it idles ok. I am lost at this one.

After this I was leaning on the crank sensor going bad but the car usually does not start at all if that happens, so that is counted out. also the resistance on the crank sensor checked out fine.

another thing I thought about is the timing belt jumping a teeth. How do I go about verifying that is not the timing belt?. will the car run atall with bad timing?.

any other ideas, leads??

I need your help guys/gurus out there. Thanks.!!!!!!

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