help Exhaust backfire and low idle
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From: Florida
help Exhaust backfire and low idle
Currently im facing a issue with my 92 sc300 Automatic it was a couple of weeks back when it started doing this i have read over 20 threads but no luck. I was replacing my tps sensor after my old one had broke apart and i ordered a aftermarket unit from amazon. Once i had it installed i drove around and remembered i had forgot to reconnect the exhaust side valve cover metal PVC hose to the intake and i pulled over to the side to reconnect the hose. After reconnecting the hose i noticed my iacv valve plug was slipping and while trying to reconnect it the whole plug slipped off , it sparked and the car shut off. After 30ish mins of trying to reconnect the pins ( the connector was destroyed previously) and the efi fuse was burned. After fixing these the car started up right away and the ride back i could feel the exhaust backfiring. Anyway i thought the problem would have been solved by resetting the ecu but thats not the case. As of now the car will idle like brand new on cold starts and once warm ( above the halfway mark i believe ) the exhaust backfire will start. I also idle at 400 rpm or at-least used to before resetting my ecu. I have no noticeable effects while my car is running the car only suffers from this backfire while in Park but 400 rpm idle is also there at stop lights.
Some other things i have done
Egr delete a while ago never experienced this this is my routing setting up. I have 1 vacuum hose from canister to a t connecting the hardline and the plenum. Next i have the butterfly valve in between the y pipe connected to a black hardline. Next is my fpr (next to vsv) connected to my intake plenum next is the last line is 1 line from the top 4 hose lines on the throttle body to the butterfly valve near the tps.
Got a oem tps
replaced Iacv
checked the ecu about 1 month before this it was fine
Unplugged the MAF while car was running heres the strange part when cold the MAF shuts off the car but when warm the car has no problem running.
i tried moving the tps towards the driver side to see if i could change anything there was change but the backfire did not stop.
The passenger side tps i am assuming has no effect in idle.
I did put in new NGK sparkplugs before the iacv disconnecting could me trying to turn over the motor kill the sparkplugs?
Most recently i spotted my PCV valve grommet was a bit cracked so i replaced it but im sure the PCV is fine it was replaced 1-2 months ago but i dont really know if this is new but the car revs up a bit high and then back to steady rpm (1000) on cold starts now after the new grommet its made by dorman.
Some other things i have done
Egr delete a while ago never experienced this this is my routing setting up. I have 1 vacuum hose from canister to a t connecting the hardline and the plenum. Next i have the butterfly valve in between the y pipe connected to a black hardline. Next is my fpr (next to vsv) connected to my intake plenum next is the last line is 1 line from the top 4 hose lines on the throttle body to the butterfly valve near the tps.
Got a oem tps
replaced Iacv
checked the ecu about 1 month before this it was fine
Unplugged the MAF while car was running heres the strange part when cold the MAF shuts off the car but when warm the car has no problem running.
i tried moving the tps towards the driver side to see if i could change anything there was change but the backfire did not stop.
The passenger side tps i am assuming has no effect in idle.
I did put in new NGK sparkplugs before the iacv disconnecting could me trying to turn over the motor kill the sparkplugs?
Most recently i spotted my PCV valve grommet was a bit cracked so i replaced it but im sure the PCV is fine it was replaced 1-2 months ago but i dont really know if this is new but the car revs up a bit high and then back to steady rpm (1000) on cold starts now after the new grommet its made by dorman.
What engine codes are you seeing?
It sounds like something was damaged, maybe a sensor, when the IACV wire grounded out. It's quite possible since you say the connector shattered that the 12v wire touched a few other wires on that connector. You replaced the main EFI fuse but there's something else that was damaged during that power surge. Either another fuse, or a sensor that shares the same circuits as the IACV. Or even the ECU.
There's also a chance that when you repinned the IACV connector, you pinned the wires in the wrong order.
What you describe sounds like the car works fine while it is in open loop. That's when the car runs purely off the programming parameters in the ecu. The car uses this on startup up until the coolant gets warm, and also when there is a CEL. Once it is warm enough, the ecu goes into closed loop and that is when the ECU reads all the sensors on the engine and determines timing and A/F ratios.
I believe this is your case because you say the car has no issues starting cold (sometimes cold idle can be as high as 1600rpm) but once it warms up the backfiring starts.
You also say that when you unplug the MAF, the car suddenly runs fine. That's because unplugging the MAF triggers a CEL and that automatically switches the ECU programming from closed loop to open loop.
You never say it, but when you replaced the TPS sensor, did you calibrate it? They need to be calibrated. That requires measuring voltage and adjusting it. There are threads on here and in Supraforums as you how to calibrate TPS sensors. It is also critical that you use a GE TPS on a GE motor and the GTE TPS on the GTE motor.
I don't think any of this is related to your EGR delete or your vacuum hoses since if it was, you would've had these issues before the IACV valve grounded out.
It sounds like something was damaged, maybe a sensor, when the IACV wire grounded out. It's quite possible since you say the connector shattered that the 12v wire touched a few other wires on that connector. You replaced the main EFI fuse but there's something else that was damaged during that power surge. Either another fuse, or a sensor that shares the same circuits as the IACV. Or even the ECU.
There's also a chance that when you repinned the IACV connector, you pinned the wires in the wrong order.
What you describe sounds like the car works fine while it is in open loop. That's when the car runs purely off the programming parameters in the ecu. The car uses this on startup up until the coolant gets warm, and also when there is a CEL. Once it is warm enough, the ecu goes into closed loop and that is when the ECU reads all the sensors on the engine and determines timing and A/F ratios.
I believe this is your case because you say the car has no issues starting cold (sometimes cold idle can be as high as 1600rpm) but once it warms up the backfiring starts.
You also say that when you unplug the MAF, the car suddenly runs fine. That's because unplugging the MAF triggers a CEL and that automatically switches the ECU programming from closed loop to open loop.
You never say it, but when you replaced the TPS sensor, did you calibrate it? They need to be calibrated. That requires measuring voltage and adjusting it. There are threads on here and in Supraforums as you how to calibrate TPS sensors. It is also critical that you use a GE TPS on a GE motor and the GTE TPS on the GTE motor.
I don't think any of this is related to your EGR delete or your vacuum hoses since if it was, you would've had these issues before the IACV valve grounded out.
^^ good info. I would say re-calibrate the TPS by the book or something else got shorted or up with the IACV wiring.
I am also assuming repairing means you put on a new connector and made sure the wires were in good shape.
I forget if that has both 12V and 5v on that IACV plug (*edit* I looked it up looks like just 12V on this plug)
If you short out something with 5v on these cars chances are the ecu is then bad since the ecu supplies the power for 5v stuff (95 and under karman maf's are 5v, newer hotwire 96+ is 12v).
There is no fuse if the 5v driver is blown that I know of without going in to repair stuff.
If the IACV plug only has 12v wires, then those would short fuses in the bay that you can change out or repair.
I would check for voltage at the maf power and ground to confirm the 5v is still working just to be sure since you said you were slipping the maf connector on and off while running (probably not a good idea to keep doing).
Basically without codes hard to say you will have to go through step by step, but the tps position can affect the warmed up running if its not calibrated right, stock ecu is very sensitive to tps changes.
I am also assuming repairing means you put on a new connector and made sure the wires were in good shape.
I forget if that has both 12V and 5v on that IACV plug (*edit* I looked it up looks like just 12V on this plug)
If you short out something with 5v on these cars chances are the ecu is then bad since the ecu supplies the power for 5v stuff (95 and under karman maf's are 5v, newer hotwire 96+ is 12v).
There is no fuse if the 5v driver is blown that I know of without going in to repair stuff.
If the IACV plug only has 12v wires, then those would short fuses in the bay that you can change out or repair.
I would check for voltage at the maf power and ground to confirm the 5v is still working just to be sure since you said you were slipping the maf connector on and off while running (probably not a good idea to keep doing).
Basically without codes hard to say you will have to go through step by step, but the tps position can affect the warmed up running if its not calibrated right, stock ecu is very sensitive to tps changes.
Last edited by Ali SC3; Feb 26, 2020 at 02:18 PM.
Thread Starter
Rookie
Joined: Sep 2019
Posts: 71
Likes: 1
From: Florida
thanks for the help
Thanks for the reply when i first replaced the tps i used a aftermarket model that i ordered from amazon. I suspected this was the issue so i got a oem tps from a ls400 (same part number) from a junkyard and the pins on my multi meter dont fit in tps plug in area to i attempted to calibrate the tps by feel when the car was on. Also unplugging the MAF does not make the car run better it just dosent effect anything when the car is warm or the backfire starts, but when the car is cold leaving the car does experience change and it runs worse.
What engine codes are you seeing?
It sounds like something was damaged, maybe a sensor, when the IACV wire grounded out. It's quite possible since you say the connector shattered that the 12v wire touched a few other wires on that connector. You replaced the main EFI fuse but there's something else that was damaged during that power surge. Either another fuse, or a sensor that shares the same circuits as the IACV. Or even the ECU.
There's also a chance that when you repinned the IACV connector, you pinned the wires in the wrong order.
What you describe sounds like the car works fine while it is in open loop. That's when the car runs purely off the programming parameters in the ecu. The car uses this on startup up until the coolant gets warm, and also when there is a CEL. Once it is warm enough, the ecu goes into closed loop and that is when the ECU reads all the sensors on the engine and determines timing and A/F ratios.
I believe this is your case because you say the car has no issues starting cold (sometimes cold idle can be as high as 1600rpm) but once it warms up the backfiring starts.
You also say that when you unplug the MAF, the car suddenly runs fine. That's because unplugging the MAF triggers a CEL and that automatically switches the ECU programming from closed loop to open loop.
You never say it, but when you replaced the TPS sensor, did you calibrate it? They need to be calibrated. That requires measuring voltage and adjusting it. There are threads on here and in Supraforums as you how to calibrate TPS sensors. It is also critical that you use a GE TPS on a GE motor and the GTE TPS on the GTE motor.
I don't think any of this is related to your EGR delete or your vacuum hoses since if it was, you would've had these issues before the IACV valve grounded out.
It sounds like something was damaged, maybe a sensor, when the IACV wire grounded out. It's quite possible since you say the connector shattered that the 12v wire touched a few other wires on that connector. You replaced the main EFI fuse but there's something else that was damaged during that power surge. Either another fuse, or a sensor that shares the same circuits as the IACV. Or even the ECU.
There's also a chance that when you repinned the IACV connector, you pinned the wires in the wrong order.
What you describe sounds like the car works fine while it is in open loop. That's when the car runs purely off the programming parameters in the ecu. The car uses this on startup up until the coolant gets warm, and also when there is a CEL. Once it is warm enough, the ecu goes into closed loop and that is when the ECU reads all the sensors on the engine and determines timing and A/F ratios.
I believe this is your case because you say the car has no issues starting cold (sometimes cold idle can be as high as 1600rpm) but once it warms up the backfiring starts.
You also say that when you unplug the MAF, the car suddenly runs fine. That's because unplugging the MAF triggers a CEL and that automatically switches the ECU programming from closed loop to open loop.
You never say it, but when you replaced the TPS sensor, did you calibrate it? They need to be calibrated. That requires measuring voltage and adjusting it. There are threads on here and in Supraforums as you how to calibrate TPS sensors. It is also critical that you use a GE TPS on a GE motor and the GTE TPS on the GTE motor.
I don't think any of this is related to your EGR delete or your vacuum hoses since if it was, you would've had these issues before the IACV valve grounded out.
Thread Starter
Rookie
Joined: Sep 2019
Posts: 71
Likes: 1
From: Florida
Also there are no codes
What engine codes are you seeing?
It sounds like something was damaged, maybe a sensor, when the IACV wire grounded out. It's quite possible since you say the connector shattered that the 12v wire touched a few other wires on that connector. You replaced the main EFI fuse but there's something else that was damaged during that power surge. Either another fuse, or a sensor that shares the same circuits as the IACV. Or even the ECU.
There's also a chance that when you repinned the IACV connector, you pinned the wires in the wrong order.
What you describe sounds like the car works fine while it is in open loop. That's when the car runs purely off the programming parameters in the ecu. The car uses this on startup up until the coolant gets warm, and also when there is a CEL. Once it is warm enough, the ecu goes into closed loop and that is when the ECU reads all the sensors on the engine and determines timing and A/F ratios.
I believe this is your case because you say the car has no issues starting cold (sometimes cold idle can be as high as 1600rpm) but once it warms up the backfiring starts.
You also say that when you unplug the MAF, the car suddenly runs fine. That's because unplugging the MAF triggers a CEL and that automatically switches the ECU programming from closed loop to open loop.
You never say it, but when you replaced the TPS sensor, did you calibrate it? They need to be calibrated. That requires measuring voltage and adjusting it. There are threads on here and in Supraforums as you how to calibrate TPS sensors. It is also critical that you use a GE TPS on a GE motor and the GTE TPS on the GTE motor.
I don't think any of this is related to your EGR delete or your vacuum hoses since if it was, you would've had these issues before the IACV valve grounded out.
It sounds like something was damaged, maybe a sensor, when the IACV wire grounded out. It's quite possible since you say the connector shattered that the 12v wire touched a few other wires on that connector. You replaced the main EFI fuse but there's something else that was damaged during that power surge. Either another fuse, or a sensor that shares the same circuits as the IACV. Or even the ECU.
There's also a chance that when you repinned the IACV connector, you pinned the wires in the wrong order.
What you describe sounds like the car works fine while it is in open loop. That's when the car runs purely off the programming parameters in the ecu. The car uses this on startup up until the coolant gets warm, and also when there is a CEL. Once it is warm enough, the ecu goes into closed loop and that is when the ECU reads all the sensors on the engine and determines timing and A/F ratios.
I believe this is your case because you say the car has no issues starting cold (sometimes cold idle can be as high as 1600rpm) but once it warms up the backfiring starts.
You also say that when you unplug the MAF, the car suddenly runs fine. That's because unplugging the MAF triggers a CEL and that automatically switches the ECU programming from closed loop to open loop.
You never say it, but when you replaced the TPS sensor, did you calibrate it? They need to be calibrated. That requires measuring voltage and adjusting it. There are threads on here and in Supraforums as you how to calibrate TPS sensors. It is also critical that you use a GE TPS on a GE motor and the GTE TPS on the GTE motor.
I don't think any of this is related to your EGR delete or your vacuum hoses since if it was, you would've had these issues before the IACV valve grounded out.
Thread Starter
Rookie
Joined: Sep 2019
Posts: 71
Likes: 1
From: Florida
thanks for the help I’ll test and update
^^ good info. I would say re-calibrate the TPS by the book or something else got shorted or up with the IACV wiring.
I am also assuming repairing means you put on a new connector and made sure the wires were in good shape.
I forget if that has both 12V and 5v on that IACV plug (*edit* I looked it up looks like just 12V on this plug)
If you short out something with 5v on these cars chances are the ecu is then bad since the ecu supplies the power for 5v stuff (95 and under karman maf's are 5v, newer hotwire 96+ is 12v).
There is no fuse if the 5v driver is blown that I know of without going in to repair stuff.
If the IACV plug only has 12v wires, then those would short fuses in the bay that you can change out or repair.
I would check for voltage at the maf power and ground to confirm the 5v is still working just to be sure since you said you were slipping the maf connector on and off while running (probably not a good idea to keep doing).
Basically without codes hard to say you will have to go through step by step, but the tps position can affect the warmed up running if its not calibrated right, stock ecu is very sensitive to tps changes.
I am also assuming repairing means you put on a new connector and made sure the wires were in good shape.
I forget if that has both 12V and 5v on that IACV plug (*edit* I looked it up looks like just 12V on this plug)
If you short out something with 5v on these cars chances are the ecu is then bad since the ecu supplies the power for 5v stuff (95 and under karman maf's are 5v, newer hotwire 96+ is 12v).
There is no fuse if the 5v driver is blown that I know of without going in to repair stuff.
If the IACV plug only has 12v wires, then those would short fuses in the bay that you can change out or repair.
I would check for voltage at the maf power and ground to confirm the 5v is still working just to be sure since you said you were slipping the maf connector on and off while running (probably not a good idea to keep doing).
Basically without codes hard to say you will have to go through step by step, but the tps position can affect the warmed up running if its not calibrated right, stock ecu is very sensitive to tps changes.
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Thread Starter
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Joined: Sep 2019
Posts: 71
Likes: 1
From: Florida
Thanks for your help I ended up going on a rampage with the tps seeing if feel changed anything and it didnt then in decided to check if my distrubtor was off and there u have it position of that dumb nut got me good. I must of changed the timing when i was changing the O ring anyway I set my tps with a multimeter now just gotta get myself a timing light for the distrubtor.
If you take the distributor out there is a good chance it won't go back in exactly the same cause the cam gear will rotate it as it goes in.
I always check with the light after reinstalling one. good luck!
I always check with the light after reinstalling one. good luck!
Thread Starter
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Joined: Sep 2019
Posts: 71
Likes: 1
From: Florida
Ya it’s not the rotor position that was wrong it was the position of the nut and turning the distributor anyway everything is back to factory spec 
And I only wasted 20 bucks on a new iacv lol. I’m very thankful it’s not a wiring issue
And I only wasted 20 bucks on a new iacv lol. I’m very thankful it’s not a wiring issue
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Oct 22, 2009 06:51 AM