This is about my 2001 Dodge Dakota. 3.9 liter V6 with a 5 speed manual. 165,200 miles on the odometer now. Old school cast iron Mopar Magnum engine, it has no EGR.
I have been trying for about 4 weeks now to fix an odd problem with the idle in my truck. Normally it will start right up and idle at 700 RPM, no matter what the temperature or weather might be. About a month ago it had a no start here at home. Engine cranked and started but had a very low idle and died. I tried it again, it turned over fine but just would not start. I let it sit a few minutes and did get it started but the idle was very low, maybe around 200 or 300 and I had to pump the throttle to keep it going. I held the throttle at about 1200 RPM a minute or so and let off, then the truck idled and drove fine after that.
That exact same starting/idling problem has continued up until now, but I only had a no-start that one time. If the truck sits overnight, and I start it in the morning it will idle low, 200 to 300 RPM for a few seconds, run rough and die. If I goose the throttle a bit and hold it upwards of 1000 RPM for maybe 20 or 30 seconds the idle returns to normal and the truck will run just fine all the way to work, which is 20 miles one way. When I leave work in the afternoon, the truck starts, idles and runs fine right away and all the way home. Then the next morning, same thing again with the low rough idle and it dies unless I goose and hold the throttle.
I have done a lot of things over the last 3 or 4 weeks trying to fix this problem:
New plugs, Autolite 3923's. They are not the OEM spec plug but I have used them nearly all of the time I have owned my truck, and it runs great on them. Gapped at stock gap spec, .040.
Cleaned throttle body with throttle body cleaner spray
New Autolite Professional plug wires
Distributor cap and rotor, Napa Echlin parts
New Duralast Gold battery, pro-rated warranty exchange
New Throttle Position Sensor, Duralast brand
New Idle Air Control Valve, BWD brand from AAP
Back in November, long before this cold idle problem ever started I replaced the two mini-cats and main cat with an Eastern Catalytic assembly from Rock Auto. Also in November I replaced both downstream O2's. Upstream O2's have about 50,000 miles on them. All 4 O2's are NTK.
I have also sprayed carb cleaner around the engine trying to find any vacuum leaks. The idle never changed no matter where I sprayed the carb cleaner.
This past Friday I checked my Intake Air Temperature sensor, it was about 200 ohms out of spec on a hot idle so I replaced it with a BWD sensor from AAP. My scan tool tells me the Engine Coolant Temp sensor is steady at 182 degrees so I believe it is OK. I use a 180 degree t-stat and the colder heat range Autolite 3923 plugs to help avoid preignition ping, which is a common problem on Dodge Magnum engines.
I checked the fuel pressure, the engine was cold but I put my fuel pressure gauge on the test port then got it running here at home, at 700 RPM I had 50 psi. I shut the truck off, left the gauge connected and 10 minutes later there was still 40 psi in the fuel rail.
I replaced my fuel pump about 40,000 miles and 4 years ago. I used an Airtex pump that I bought from AAP with an online discount code. I have since read about problems with Airtex pumps but never had any problems with mine until now. The pump I bought only had a one year warranty, but Airtex now carries a lifetime warranty. AAP just now told me most likely they will have to go by the original warranty (which expired 3 years ago) or I can try to ask the store manager if he can do some kind of good-faith good customer return on it for a new one.
Now to my question. Someone told me last week the fuel pressure can still be within specs whether the engine is running or not but if there is a problem with the fuel filter it can cause this kind of wonky idle problem. The filter is a sock at the bottom of the fuel pump. The same guy also told me the fuel outlet at the top of the pump also works as a filter and can become clogged with dirt/debris which can cause the same problem with normal fuel pressure yet a bad idle on a cold start because the fuel volume is reduced when the filters are dirty. There is no external fuel filter on my truck.
Even if I do need a new fuel pump I am not so sure I will go with Airtex again after this problem and reading about other Airtex issues. I am trying to find out if anyone here has seen a similar problem where the car ran fine when warmed up but wold not idle on a cold start due to lower fuel volume, and if so then did/would a new fuel pump solve the problem?
Sorry for such a long post here but I figure the info is relevant to help me get some ideas of whether to replace the fuel pump. I appreciate any help.
I have been trying for about 4 weeks now to fix an odd problem with the idle in my truck. Normally it will start right up and idle at 700 RPM, no matter what the temperature or weather might be. About a month ago it had a no start here at home. Engine cranked and started but had a very low idle and died. I tried it again, it turned over fine but just would not start. I let it sit a few minutes and did get it started but the idle was very low, maybe around 200 or 300 and I had to pump the throttle to keep it going. I held the throttle at about 1200 RPM a minute or so and let off, then the truck idled and drove fine after that.
That exact same starting/idling problem has continued up until now, but I only had a no-start that one time. If the truck sits overnight, and I start it in the morning it will idle low, 200 to 300 RPM for a few seconds, run rough and die. If I goose the throttle a bit and hold it upwards of 1000 RPM for maybe 20 or 30 seconds the idle returns to normal and the truck will run just fine all the way to work, which is 20 miles one way. When I leave work in the afternoon, the truck starts, idles and runs fine right away and all the way home. Then the next morning, same thing again with the low rough idle and it dies unless I goose and hold the throttle.
I have done a lot of things over the last 3 or 4 weeks trying to fix this problem:
New plugs, Autolite 3923's. They are not the OEM spec plug but I have used them nearly all of the time I have owned my truck, and it runs great on them. Gapped at stock gap spec, .040.
Cleaned throttle body with throttle body cleaner spray
New Autolite Professional plug wires
Distributor cap and rotor, Napa Echlin parts
New Duralast Gold battery, pro-rated warranty exchange
New Throttle Position Sensor, Duralast brand
New Idle Air Control Valve, BWD brand from AAP
Back in November, long before this cold idle problem ever started I replaced the two mini-cats and main cat with an Eastern Catalytic assembly from Rock Auto. Also in November I replaced both downstream O2's. Upstream O2's have about 50,000 miles on them. All 4 O2's are NTK.
I have also sprayed carb cleaner around the engine trying to find any vacuum leaks. The idle never changed no matter where I sprayed the carb cleaner.
This past Friday I checked my Intake Air Temperature sensor, it was about 200 ohms out of spec on a hot idle so I replaced it with a BWD sensor from AAP. My scan tool tells me the Engine Coolant Temp sensor is steady at 182 degrees so I believe it is OK. I use a 180 degree t-stat and the colder heat range Autolite 3923 plugs to help avoid preignition ping, which is a common problem on Dodge Magnum engines.
I checked the fuel pressure, the engine was cold but I put my fuel pressure gauge on the test port then got it running here at home, at 700 RPM I had 50 psi. I shut the truck off, left the gauge connected and 10 minutes later there was still 40 psi in the fuel rail.
I replaced my fuel pump about 40,000 miles and 4 years ago. I used an Airtex pump that I bought from AAP with an online discount code. I have since read about problems with Airtex pumps but never had any problems with mine until now. The pump I bought only had a one year warranty, but Airtex now carries a lifetime warranty. AAP just now told me most likely they will have to go by the original warranty (which expired 3 years ago) or I can try to ask the store manager if he can do some kind of good-faith good customer return on it for a new one.
Now to my question. Someone told me last week the fuel pressure can still be within specs whether the engine is running or not but if there is a problem with the fuel filter it can cause this kind of wonky idle problem. The filter is a sock at the bottom of the fuel pump. The same guy also told me the fuel outlet at the top of the pump also works as a filter and can become clogged with dirt/debris which can cause the same problem with normal fuel pressure yet a bad idle on a cold start because the fuel volume is reduced when the filters are dirty. There is no external fuel filter on my truck.
Even if I do need a new fuel pump I am not so sure I will go with Airtex again after this problem and reading about other Airtex issues. I am trying to find out if anyone here has seen a similar problem where the car ran fine when warmed up but wold not idle on a cold start due to lower fuel volume, and if so then did/would a new fuel pump solve the problem?
Sorry for such a long post here but I figure the info is relevant to help me get some ideas of whether to replace the fuel pump. I appreciate any help.
