Rough idle 3 min after start-up.
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Amateur
Joined: Apr 2009
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From: Minnesota
Rough idle 3 min after start-up.
Hello fellow Ram owners, I'm new to this forum and would like some help with my 99 Ram 1500 5.2L 4x2. The problem occurs about 3 mins after start-up. It starts hissing coming from the carb and begins to run rough. This lasts about 4-5 min then the hissing stops and it returns to a smooth idle. If I try to drive my truck during the rough idle period, it has a loss of power and backfires occationally. This goes away after the 4-5 min duration but this happens everytime, even if the engine is warmed up. Any ideas what to look for?
Thank You
Dan
Thank You
Dan
Captain
Joined: Mar 2004
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From: Plant City, FL
Welcome to the forum. You've come to the right place!
Sounds like the IAC valve isn't working like it should. The fact that it is OK until the engine warms up could also indicate something possibly wrong with the pre-cat O2 sensor. I'm no mechanic, but this is what first comes to mind. Maybe somebody will chime in who actually knows about these things.
Sounds like the IAC valve isn't working like it should. The fact that it is OK until the engine warms up could also indicate something possibly wrong with the pre-cat O2 sensor. I'm no mechanic, but this is what first comes to mind. Maybe somebody will chime in who actually knows about these things.
Last edited by ron333; Apr 24, 2009 at 09:30 AM. Reason: Added "Welcome..."
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From: Allentown, PA
Hello fellow Ram owners, I'm new to this forum and would like some help with my 99 Ram 1500 5.2L 4x2. The problem occurs about 3 mins after start-up. It starts hissing coming from the TB and begins to run rough. This lasts about 4-5 min then the hissing stops and it returns to a smooth idle. If I try to drive my truck during the rough idle period, it has a loss of power and backfires occationally. This goes away after the 4-5 min duration but this happens everytime, even if the engine is warmed up. Any ideas what to look for?
Thank You
Dan
Thank You
Dan
Thread Starter
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Amateur
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From: Minnesota
Well I cleaned the IAC and I've noticed the hissing sound and rough idle has stopped, but when I drive it right after start-up, it still labors and backfires for a couple of minutes then clears up and runs fine. Even if the engine is warm, if I shut it off for a few minutes it does it again. Any other ideas?
Thanks
Dan
Thanks
Dan
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Joined: Apr 2009
Posts: 27
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From: Houston, TX
Ok let me think this through with you. I am working on an idle problem thats how I came across this post. What happens at startup? Lets try a couple of things.
1. I saw a simular problem at startup but would run fine after 30-45 seconds. Try this and see if the problem goes away. Turn the key to on (not start) wait for 3 seconds, then turn off. DO this about 4 times quickly, then start and see if the problem goes away. If it does then I would check fuel system. I found a bad hose in the fuel pump assyembly that was bleeding off the fuel pressure and it took a little bit for the fuel pressure to build up enough for the car to run. After the pressure was up then everything ran fine.
2. Vacuum leak? I would inspect all vacuum lines for cracks.
3. Try removing the oil fill cap holding it just above the valve cover and see if the idle changes drastically. If so replace the PVC valve from OEM. An inexpensive replacement part and can cause rough idle and should be replaced on regular intervals. Removing the cover increases suction or pressure into the intake by closing the pvc valve, if the valve is working correclty.
4. If this problem only occurs at start up, hot cold or whatever, I would also look to see if you have a cold start valve is sometimes called the fifth injector. It is mounted to the intake air distribution box and is in line with the fuel rail. It has an electrical connection and a fuel inlet line and a fuel outlet line. The cold start valve is essentially constructed the same as the regular fuel injectors. The main difference is that the cold start valve injection time is measured in seconds rather than in milliseconds like the regular injectors.
The cold start valve receives power from the double relay when the key is in the start position but only injects fuel into the intake air distributor when the cold start valve is grounded by the thermo-time switch.
The purpose of the cold start valve is to inject fuel into the intake air stream when the engine is cold (and the starter operating) in order to richen the fuel/air mixture for easier starting. It can be tested in the same manner as the other injectors. Leakage is undesirable as it will cause the engine to run rich. This valve could be putting out to much fuel at startup causing flooding and rough idle. Try disconnecting the electrical connection to this valve and see if the problem goes away.
Let us know what you find.
Last thing I would have the fuel pressure checked if you can and see what you find.
Good luck
1. I saw a simular problem at startup but would run fine after 30-45 seconds. Try this and see if the problem goes away. Turn the key to on (not start) wait for 3 seconds, then turn off. DO this about 4 times quickly, then start and see if the problem goes away. If it does then I would check fuel system. I found a bad hose in the fuel pump assyembly that was bleeding off the fuel pressure and it took a little bit for the fuel pressure to build up enough for the car to run. After the pressure was up then everything ran fine.
2. Vacuum leak? I would inspect all vacuum lines for cracks.
3. Try removing the oil fill cap holding it just above the valve cover and see if the idle changes drastically. If so replace the PVC valve from OEM. An inexpensive replacement part and can cause rough idle and should be replaced on regular intervals. Removing the cover increases suction or pressure into the intake by closing the pvc valve, if the valve is working correclty.
4. If this problem only occurs at start up, hot cold or whatever, I would also look to see if you have a cold start valve is sometimes called the fifth injector. It is mounted to the intake air distribution box and is in line with the fuel rail. It has an electrical connection and a fuel inlet line and a fuel outlet line. The cold start valve is essentially constructed the same as the regular fuel injectors. The main difference is that the cold start valve injection time is measured in seconds rather than in milliseconds like the regular injectors.
The cold start valve receives power from the double relay when the key is in the start position but only injects fuel into the intake air distributor when the cold start valve is grounded by the thermo-time switch.
The purpose of the cold start valve is to inject fuel into the intake air stream when the engine is cold (and the starter operating) in order to richen the fuel/air mixture for easier starting. It can be tested in the same manner as the other injectors. Leakage is undesirable as it will cause the engine to run rich. This valve could be putting out to much fuel at startup causing flooding and rough idle. Try disconnecting the electrical connection to this valve and see if the problem goes away.
Let us know what you find.
Last thing I would have the fuel pressure checked if you can and see what you find.
Good luck
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Amateur
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From: Minnesota
Sorry I haven't gotten back to you on this, been out of state. The problem seems to have worked itself out slightly. I can feel it missing when I drive right after I start it, then it goes away. It's not as bad as it was after I cleaned the IAC and TB. I'll look into your suggestions and see what I find. I'll also check my plug wires and see if that might be an issue. Thanks for your help.
Dan
Dan
Ok let me think this through with you. I am working on an idle problem thats how I came across this post. What happens at startup? Lets try a couple of things.
1. I saw a simular problem at startup but would run fine after 30-45 seconds. Try this and see if the problem goes away. Turn the key to on (not start) wait for 3 seconds, then turn off. DO this about 4 times quickly, then start and see if the problem goes away. If it does then I would check fuel system. I found a bad hose in the fuel pump assyembly that was bleeding off the fuel pressure and it took a little bit for the fuel pressure to build up enough for the car to run. After the pressure was up then everything ran fine.
2. Vacuum leak? I would inspect all vacuum lines for cracks.
3. Try removing the oil fill cap holding it just above the valve cover and see if the idle changes drastically. If so replace the PVC valve from OEM. An inexpensive replacement part and can cause rough idle and should be replaced on regular intervals. Removing the cover increases suction or pressure into the intake by closing the pvc valve, if the valve is working correclty.
4. If this problem only occurs at start up, hot cold or whatever, I would also look to see if you have a cold start valve is sometimes called the fifth injector. It is mounted to the intake air distribution box and is in line with the fuel rail. It has an electrical connection and a fuel inlet line and a fuel outlet line. The cold start valve is essentially constructed the same as the regular fuel injectors. The main difference is that the cold start valve injection time is measured in seconds rather than in milliseconds like the regular injectors.
The cold start valve receives power from the double relay when the key is in the start position but only injects fuel into the intake air distributor when the cold start valve is grounded by the thermo-time switch.
The purpose of the cold start valve is to inject fuel into the intake air stream when the engine is cold (and the starter operating) in order to richen the fuel/air mixture for easier starting. It can be tested in the same manner as the other injectors. Leakage is undesirable as it will cause the engine to run rich. This valve could be putting out to much fuel at startup causing flooding and rough idle. Try disconnecting the electrical connection to this valve and see if the problem goes away.
Let us know what you find.
Last thing I would have the fuel pressure checked if you can and see what you find.
Good luck
1. I saw a simular problem at startup but would run fine after 30-45 seconds. Try this and see if the problem goes away. Turn the key to on (not start) wait for 3 seconds, then turn off. DO this about 4 times quickly, then start and see if the problem goes away. If it does then I would check fuel system. I found a bad hose in the fuel pump assyembly that was bleeding off the fuel pressure and it took a little bit for the fuel pressure to build up enough for the car to run. After the pressure was up then everything ran fine.
2. Vacuum leak? I would inspect all vacuum lines for cracks.
3. Try removing the oil fill cap holding it just above the valve cover and see if the idle changes drastically. If so replace the PVC valve from OEM. An inexpensive replacement part and can cause rough idle and should be replaced on regular intervals. Removing the cover increases suction or pressure into the intake by closing the pvc valve, if the valve is working correclty.
4. If this problem only occurs at start up, hot cold or whatever, I would also look to see if you have a cold start valve is sometimes called the fifth injector. It is mounted to the intake air distribution box and is in line with the fuel rail. It has an electrical connection and a fuel inlet line and a fuel outlet line. The cold start valve is essentially constructed the same as the regular fuel injectors. The main difference is that the cold start valve injection time is measured in seconds rather than in milliseconds like the regular injectors.
The cold start valve receives power from the double relay when the key is in the start position but only injects fuel into the intake air distributor when the cold start valve is grounded by the thermo-time switch.
The purpose of the cold start valve is to inject fuel into the intake air stream when the engine is cold (and the starter operating) in order to richen the fuel/air mixture for easier starting. It can be tested in the same manner as the other injectors. Leakage is undesirable as it will cause the engine to run rich. This valve could be putting out to much fuel at startup causing flooding and rough idle. Try disconnecting the electrical connection to this valve and see if the problem goes away.
Let us know what you find.
Last thing I would have the fuel pressure checked if you can and see what you find.
Good luck
Thread Starter
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Amateur
Joined: Apr 2009
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From: Minnesota
Mine was located on the back of the throttle body, It's held on with 2 torx screws and has an electrical connector attached. I cleaned it and inside the TB with Q-tips and carb cleaner.
HTH
Dan