Car dies coming down from high rpm's

alexscof · 11-23-2009, 07:36 AM

Hey guys, ever since I got my car, I've had a problem with it dying. Its worst when its cold but has happened when the motor is warm too. If I'm above about 2500 rpm and put the clutch in, the rpm's drop and it usually it dies. Sometimes it chatches itself but the higher the rpm's the more likely it will die. I can downshift and tap the throttle when im slowing down but I'd really like to fix this problem.

Thanks, any help is appreciated.

89 supra JDM 7mgte w/ R154.

boner1115 · 11-23-2009, 10:09 AM

Are you basing this off of when matt drives. Because when he is driving it dies all the time just because he cant drive a stick.

boner1115 · 11-23-2009, 10:10 AM

it occurred to me that no one else here is going get that joke except Alex haha.

oh well

cre · 11-23-2009, 06:19 PM

Are you running with a recirculating BOV or a BOV that's venting to atmosphere? Do you have a wideband? It'd be nice to see what the AFRs are when this happens. Do you have any error codes and is the TPS properly calibrated?

I'm surprised it's dying when you let off from an RPM higher than 2000, typically the dashpot at least prevents the throttle plate from slapping shut before the ECU can adjust fueling... it's not the cause of the problem, but it is indicative of a probelm with the dashpot too.

alexscof · 11-23-2009, 10:51 PM

Everything on the car is stock except the bov. It's an HKS the guy I bought the car from put on. Forgive my ignorance, a couple of your questions went right over my head. The check engine light does come on but its as the car is dying so all of the lights on the display light up. I attached a picture of my bov.

cre · 11-23-2009, 11:04 PM

Error codes, check them:
http://www.cygnusx1.net/Supra/TechTi...ror_codes.aspx

Very few diagnostic errors actually result in the CEL remaining on.

TPS (Throttle Position Sensor) calibration:
http://www.cygnusx1.net/Supra/Librar...ction=FI&P=100

Does the vehicle have any aftermarket fuel management? Such as a piggyback system for adjusting the fuel (Apex'i SAFC, Apex'i Neo, MAFT Gen II, MAFT Pro)...

The BOV venting to atmosphere is probably the bulk of your problem, it's been covered here recently so do a search for all the details. Venting to the atmosphere on a system that isn't built/tuned for it causes the ECU to think there's still more air coming to the engine than there really is because the air it's already measured has just been tossed completely out of the system. For some people this simply causes the car to stumble everytime they shift and for others it flat out stalls.

If you've got the stock parts, try swapping the recirculating BOV (aka bypass valve or BPV) back on and see if the issues go away.

Check for error codes first though, there are other possible causes for this problem.

alexscof · 11-23-2009, 11:16 PM

Great, thanks for your help!

11-23-2009, 07:36 AM	#1
alexscof Stock Join Date: Nov 2009 Location: Lynnwood, WA Posts: 3	Car dies coming down from high rpm's Hey guys, ever since I got my car, I've had a problem with it dying. Its worst when its cold but has happened when the motor is warm too. If I'm above about 2500 rpm and put the clutch in, the rpm's drop and it usually it dies. Sometimes it chatches itself but the higher the rpm's the more likely it will die. I can downshift and tap the throttle when im slowing down but I'd really like to fix this problem. Thanks, any help is appreciated. 89 supra JDM 7mgte w/ R154.

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11-23-2009, 10:09 AM	#2
boner1115 Intake Join Date: Sep 2005 Posts: 36	Are you basing this off of when matt drives. Because when he is driving it dies all the time just because he cant drive a stick.

11-23-2009, 10:10 AM	#3
boner1115 Intake Join Date: Sep 2005 Posts: 36	it occurred to me that no one else here is going get that joke except Alex haha. oh well

11-23-2009, 06:19 PM	#4
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	Are you running with a recirculating BOV or a BOV that's venting to atmosphere? Do you have a wideband? It'd be nice to see what the AFRs are when this happens. Do you have any error codes and is the TPS properly calibrated? I'm surprised it's dying when you let off from an RPM higher than 2000, typically the dashpot at least prevents the throttle plate from slapping shut before the ECU can adjust fueling... it's not the cause of the problem, but it is indicative of a probelm with the dashpot too.

11-23-2009, 10:51 PM	#5
alexscof Stock Join Date: Nov 2009 Location: Lynnwood, WA Posts: 3	Everything on the car is stock except the bov. It's an HKS the guy I bought the car from put on. Forgive my ignorance, a couple of your questions went right over my head. The check engine light does come on but its as the car is dying so all of the lights on the display light up. I attached a picture of my bov.

11-23-2009, 11:04 PM	#6
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	Error codes, check them: http://www.cygnusx1.net/Supra/TechTi...ror_codes.aspx Very few diagnostic errors actually result in the CEL remaining on. TPS (Throttle Position Sensor) calibration: http://www.cygnusx1.net/Supra/Librar...ction=FI&P=100 Does the vehicle have any aftermarket fuel management? Such as a piggyback system for adjusting the fuel (Apex'i SAFC, Apex'i Neo, MAFT Gen II, MAFT Pro)... The BOV venting to atmosphere is probably the bulk of your problem, it's been covered here recently so do a search for all the details. Venting to the atmosphere on a system that isn't built/tuned for it causes the ECU to think there's still more air coming to the engine than there really is because the air it's already measured has just been tossed completely out of the system. For some people this simply causes the car to stumble everytime they shift and for others it flat out stalls. If you've got the stock parts, try swapping the recirculating BOV (aka bypass valve or BPV) back on and see if the issues go away. Check for error codes first though, there are other possible causes for this problem.

11-23-2009, 11:16 PM	#7
alexscof Stock Join Date: Nov 2009 Location: Lynnwood, WA Posts: 3	Great, thanks for your help!